Since we will have many significant up and down hill grades during our six month trip out west I want to clarify something. I have read extensively about using the transmission to both climb and the descend hills, i.e., use the same gear downhill that you used uphill. Obviously, I've also heard extensive comment on the use of the retarder to manage downhill speed. However, there seems to be a heat related result from extensive use of the retarder.
Thus my question... If one can control downhill speed with the transmission, how is use of the retarder integrated from a best practices point of view?
Thanks
Good question... I'm all 👂 this one as we are going to Colorado at the end of July
Probably a lot of different opinions on this one. I believe the rule of same gear downhill as uphill was before the engines had the horsepower they do today. If you have the VMSps you can watch trans. temps better than the gauge. The gauge seems to be slow to detect change. My way is to use the temps. as my guide, if they start to get too high I go to a lower gear. I travel over and back the Bishop grade 4 times each year and this seems to work for me.
Using the retarder properly does entail keeping an eye on transmission temperature. As transmission temperature starts to rise, back off on amount of retarder and down arrow to select a lower gear. That will give a little more engine braking and much more importantly, turn the water pump faster and therefore increase cooling.
As you know, even with Transynd, fluid life is materially affected by temperature.
To me it is a balancing act.
I was on a couple pretty steep hills with curves and a 25 mph limit for trucks. I would down shift to third and or second me use the retarder. The combination would keep,the speed well in control and not overheat the transmission.
You'll find that the trans fluid will heat faster in the higher gears. For example, if you are going down a 6% grade in 5th and use the retarder hard continually, it will heat up quickly. If you drop down into 4th you'll see it cool right down. If you want to do the whole hill in 5th just alternate between the retarder and brake. Just stab the brake to get down a bit lower than your desired speed.
jor
A little more clarification for those not familiar with mountains, heavy vehicles and air brakes.
Service brakes (brake pedal) is not used for maintaining speed of descent. That is the job of the engine, transmission and retarder/engine brake.
If you do use the service brakes because you are accelerating on a descent, apply them firmly and long enough to drop to a lower gear. Allow them to cool some. Do it again, until you reach an equilibrium speed based on "non-service brakes".
Do not PUMP air brakes. A big no no, as it can quickly deplete air supply and offers no advantage to the brakes life or in speed control.
Why all the discussion about use of brakes. Easy-- brakes do one thing for a living. They turn momentum into HEAT. While a motorhome weighs many, many times as much as a car, brake area is not that substantially larger. The brakes still have to fit inside the wheels! This applies to all heavy vehicles-- again basic physics.
From a practical standpoint, your "equilibrium speed" on a descent (where you are holding speed constant and safe without use of the service brakes) is FASTER than a loaded 18 wheeler and SLOWER than an empty one. That should give you a good starting point as you get into mountains.
I monitor our trans and engine temps via our VMSPC while going up and down grades and change gears, use the retarder and service brakes as appropriate to control those temps. AS Brett said: A Balancing Act. ^.^d
A diesel engine doesn't compression engine break the same way a gas engine does. Downshifting a diesel engine will not check or hold the speed going down a hill the same way a gas engine does. Diesels coast more. With a diesel downshifting may help reduce the speed some, but mostly the RPMs will go up.
Transmission retarders and Jake Brakes are added to heavy diesels to provide that extra resistance needed to slow down, and hold speed on descents, without relying on the service brakes.
Rather than thinking of downshifting and upshifting as controlling the coach's speed, consider thinking of downshifting and upshifting as allowing the driver to keep the RPMs in an optimal range so that:
- the coolant is pumping at a rate needed to keep the engine cool
- the transmission temperature is kept in check
- the engine does not over-rev
The retarded is added in to the mix to keep the speed in check without having to use the service brakes.
As Brett said earlier, it's a balancing act.
One thing that helped me was to go through the Foretravel manual for our coach and engine and find these three items for our transmission and engine:
- normal operating temperature range for the transmission
- normal operating temperature range for the engine
With this information you know when your setup is running within the specs, or when it is reaching an upper limit and you need to change something to bring things back into the specs. There really is no guessing or wondering.
In terms of best practices... in general, before you descend a mountain make sure the coach's speed is already at the correct speed and that you've selected the right gear. It easier to start a descent too slow and be able to speed up, than to start too fast and try to reign in speeds, temps, and RPMs. There's always that driver who pulls around you and cuts back into your lane without a thought about how heavy you are.
I've found the transmission retarder nice to use in traffic jams. It allows the coach to crawl forward at a more constant and consistent pace (like 18-wheelers do) and not be stepping on the service brakes all the time.
When we get into crowded cities there are times I've activated the retarder and kept it at setting one or two incase someone stops suddenly in front of us. This way when you stomp on the service brakes the retarder also kicks in and provides extra stopping power. It's helped several times, but you also have to be aware of what the drivers behind you are like.
Chris
I think on many coaches, once you turn the retarder switch on, it is automatically connected to pressure switches in your braking system. The more pressure on the brake foot pedal, the more retarder effect available.
If you have the multi position toggle switch on the side panel, it will apply retarding, according to position, any time your foot is not on the accelerator.
EDIT just remember, on most coaches, brake lights are not attached to retarder switch on side panel, so if you use it and not the foot brake and a big truck is following you closely..................
Ya, and that defeats my favorite "gear": COASTING!
I think this feature is sometimes not clear to drivers unfamiliar with the typical joystick setup. If you leave the retarder rocker switch on at all times, the retarder will activate every time you hit the brake. According to the the Allison user manual it applies retarding power in three increments depending how hard you are pressing the pedal. So, if you have the rocker switch on and the retarder joystick in position zero (all the way forward) the retarder is assisting your braking when you hit the pedal and you have full retarder in an emergency stop situation. You can just ignore the joystick.
jor
One of our fire trucks was a grant from the Offices of Emergency Services in California. It was a big devil and the only one with a 6 speed automatic and retarder to slow down the 10,000 lb load of water and fuel. Heading down a steep grade, we would shift down until the speed was about right for the grade. Then, if the speed started to build we would step on the retarder pedal until it slowed, release it and then used it again as the speed built until the yellow warning light came on. The engine and retarder were mostly used so we could keep the service brakes in reserve and be able to stop and cool it down if necessary.
With the U300, the Interstates are not usually that steep that I have to worry. Going down Donner Summit over I-80 west to east, I drop a gear to third, have the Jake switched on and occasionally use the service brakes to slow the coach about 2-300 RPM, release the brakes and then repeat as the speed builds. I think I only have to use the service brakes 2 or 3 times before getting down to Truckee. (I keep the Jake switched on all the time) Most of the other grades, I let aerodynamic braking plus the Jake in high gear to keep the speed to 65 or so.
With steeper highways like the 10% decent into Jackson, Wy, I generally pull over at the top and shift into the gear I think will do for the whole descent. Usually, second gear. This is so I know if I am in second gear or second direct with the transmission locked up with no surprises as we start down. I then descend, letting the RPM build to about 2000, apply the service brakes to drop that to 1700 or so, release the brakes and repeat as the speed builds. I have never overheated the brakes this way and if I were to get a hint they were getting hot, I would pull over and cool everything down. Make sure to check your air pressure before you start down and every thirty seconds on the way down.
A retarder will work about the same way and like the Jake, being more efficient at higher engine RPMs. Just watch the transmission temps as they build. Most Foretravels have transmission lockup so torque converter slippage and heating is not a factor once you get into second gear lock up (or third in some early models). It's just the retarder that will heat the fluid.
If on a two lane road during your decent, never let traffic behind dictate your speed. They can wait. Nothing wrong to use a pull out to stop and check things.
Be extra conservative as you first encounter steep descents. There is a learning curve. Once the brakes get really hot, you are in trouble.
I used to RV in a ex Greyhound with a 8V-71 Detroit, manual 4 speed and drum brakes. No Jake or retarder. The Sierras and Rockies were no big deal just using the engine and transmission with the proper gear selected and the service brakes used pretty conservatively.
Heading up any grade, downshift to keep the RPM high for efficient water pump circulation and to keep the temps in check. If the speed drops, shift down to a lower gear. Summer may have surprises with higher engine temps than your normally have in the other seasons. I don't let our water temp get much above 200 degrees ever and start shifting down well before that.
Pierce
We just have the switch,from what I have expiereinced and read here the "switch only" system seems to have less overheating.
The "switch only system" system only works when you use the foot brake. The lever on the side dash will activate the retarder anytime your are not using the accelerator. Believe this the reason why. If coming down a hill, on, will retard constantly and build up heat.
I think that is a GOOD THING! I've followed SOB coaches down steep grades and their brake lights were on all the time, so I never knew exactly what they were doing. A light tap on the brakes will give drivers behind plenty of warning. ^.^d
That's exactly what I meant.
My brake lights come on whenever the retarder is active. If I forget to push the joystick forward when I get on the highway and activate the cruise control, I'll be reminded on the next downhill stretch, as the cruise backs off the throttle, the retarder activates, and the brake lights shut off the cruise control. Instead of switching from cruising to coasting, the retarder causes noticeable "braking".
On surface streets or in traffic, I keep the joystick in position two or three, works great. And of course, it kicks in to various degrees with the service brakes.
On the highway, I automatically reach for the joystick first whenever I need to slow. Works great.
The only overheating concern comes on long descents. Here is where gear selection comes into play.
If coming down a grade with the retarder and the speed drops below some set point, either from the retatder or service brake, the transmission will automatically downshift, and the retardind becomes greatly enhanced. At this point I push the joystick all the way forward to keep from going too slow.
Tom, so you leave your stick mode retarder on all the time in the city? Does not seem very efficient, every time you take your foot of the accelerator, the retarder applies and slows you down faster. Personally I like Bretts approach and "coast", rather than the accelerate, retard/slow, accelerate, mode of driving.
I find coasting in city traffic is often too fast for me. If one notch of retard is slowing me too much, I can always push the joystick forward. It's dynamic.
I adjust the joystick as needed. Usually in city traffic, I can easily modulate the retarding with the gas pedal if Im getting too much retard. No hard and fast rule as to where to keep the joystick, sometimes in the first position, occasionally all the way forward (but with my hand in the ready. Third notch is my favorite in stop and go traffic.
I feel the retarder gives me a jump on braking faster than I can get my foot on the brakes.
Maybe I'm the only one who has a 'Pacbrake' retarder. Brett modified the location of the Allison touch pad with the retarder rocker below, my left hand fits perfect on the rocker while city driving or on 'drops'. I drive as far ahead as I can, when traffic starts to slow, foot off the gas, coast, hit the rocker and the only brake use is to a easy stop. b^.^d
Lots of good advise above. Should be required reading! Quick and dirty definition of use of brakes, retarder and transmission is:
Retarder/correct gear to maintain optimal speed on a decent.
Brakes only to check speed. They are only to slow or stop not maintain speed. Keep them cool so that they can stop you in an emergency.
Keith
When Foretravel first used the retarder in their coaches the brake lights did not come on when the retarder was activated with the lever, but they came out with a bulletin to install relays that turns on the brake lights when the retarder is activated with the lever.
Must have missed all the bulletins. Have had 4 Foretravels and have not had those relays.
Would not want them, if going down a hill with retarder on, and you had to really use your brakes for emergency, people behind you would not know, because your brake lights would have already be on. In Tom"s case where he drives with retarder lever on all the time in the city, even a worst case, people would never know when he is braking.
JMHO.
I'm content with the present setup.
Whenever I take my foot of the throttle with the retarder active, the retarder does apply braking force, slowing the rig down more than merely coasting would, hence the need for brake lights.If I don't want or need that amount of braking, I can push the joystick forward or apply slight throttle.
Anyone with a 2003 should have the same setup as I do.
Tom I have an 2003, can guarantee mine does not apply any brake lights when retarder on with stick on any position. If your brake lights stay on any time retarder [on stick], does not seem a good idea. If retarder on, and you need to stop quickly with brake pedal, brake light would already be on because you are on retard, so no indication of you braking hard. I am not talking about braking ability, I am talking about the guy behind me, and if he can tell the difference between me slowing slightly on retard, or jamming on the brakes for a emergency. Cannot imagine DOT approving a brake light system that is disabled just because the lever is in the first position, [ in my coach, 42000 lbs], 1st position is just barely slowing down coach, only slightly better slowing, than coast down. It is fine running retarder in city to slow down between throttle use if you think it necessary, but personally would not want brake light on, any time retarder is on. Rather have it when I step on the brake. To each his own.
Mine is how it came from the factory. Is yours?
Yes, if I look at 12 volt wiring, and air brake diagram, [mine anyway] brake light pressure switch is on foot brake air line, nothing connected to retarder electrical circuit. If your brake light is connected to retarder, would love to see schematic, maybe Foretravel made mine differently.
This has been discussed before. A long time before
Brake lights with retarder activity (split from Retarder Operation) (http://www.foreforums.com/index.php?topic=17679.msg118769#msg118769)
Our 95 didn't come with the joystick option, so I added it a couple of years ago, plug and play installation. I didn't add the brake light relay option so there is no brake light operation when just using the joystick, only when service brake is applied. Because I only use the retarder joystick on long downhill grades, I don't feel its necessary to have the brake lights on in that situation. Not much different than using engine braking in my opinion.
The retarder with the joystick is a great option, wouldn't want to be without it while in the mountains. Just keep a close watch on the tranny temp and engine RPM. Not difficult to find a stick position and gear that keeps all things in check. ^.^d
I've seen this dog fight before. Everyone is entitled to their opinion. Mine is if I am going down a steep grade and there are vehicles behind me, when I pull the retarder stick and start slowing down the lights will inform them. As far as the lights staying on going down a grade, they are brake lights and any new vehicles will think I am riding the brakes. I don't care what they think and they will just have to get over it.
I feel the same way, when the retarder is being used, I am braking, therefore the brake lights are on. Anyone behind me hopefully will see my lights and they will slow down also.
We added the relay, but with a dash switch can decide when and if to have brake lights on with retarder. Mostly drive with retard not activating brake lights. Relay is next to our two air brake switches mounted on forward top of metal wall in our street side forward compartment. This arrangement also keep our Jeep tow brake from activating with retarder.
Now if I only knew if the brake lights come on when we are driving the Jeep on the highway, and Adaptive Cruise Control or Emergency Braking systems automatically slows down the Jeep.
1) The city buses in St Paul have a center rear light that is green if the bus is accelerating or at steady speed, yellow if no throttle and no brake and pulsing red if braking.
2) Choose what works best for you going down hill, your comfort level and safety comes first. I use Gears, Retarder, Service Brakes in that order. Works for me.
3) Add one of these clever programmable timers to your retarder activated brake light circuit and it will let you set the brake lights to flash in any pattern or groups of patterns in any timing you want. Regular brake activation will override the pulse patterns.
You can make your regular brake lights do something too like flash three or four times and then be steady, sort of like the EMT vehicles do.
Universal Brake Light Flasher/Strober - M1 model [FLSHR_M1] - .95 : 3rd... (http://www.3rdbrakeflasher.com/brake-light-flasher-c-65/universal-brake-light-flasherstrober-m1-model-p-181.html)
Or just use them for any timing function. Want something to turn off or on in say five minutes? Like your porch light? Or water pump? These will do that. They have one that switches power and another that switches ground.
If you can think of it there is probably a solution out there to make it so.
Another reason I'm happy FT wired the brake lights to come on with the retarder is that pulling full back on the joystick does apply some serious braking. This is how I initially slow at off ramps and coming to stop signs and lights, followed by either backing off the retarder or using the brake pedal, as needed.
Letting the car behind me know I'm slowing or stopping is a good thing.
The retarder is after all a braking system.
My only concern about the retarder activating the brake lights is that I believe it also activates the toad brakes through the RoadMaster InvisiBrake. It worries me that I am wearing out the brakes on my toad. Am I understanding this correctly?
Probably. I have SMI AirForce One brakes for the toad, proportional with the coach air brakes.
I notice the retarder braking is not as effective with the toad as without. But the service brakes, aided by the retarder and toad brakes, really kick in on hard braking.
I guess it depends on your individual driving habits, I use the service brakes for braking and only use the Joystick function of the retarder for maintaining safe speed on downhill grades. Yes if you were to full throttle back on the joystick then it would be prudent to have the brake lights on to warn anyone behind you that you are rapidly decelerating. Not sure how this affects the toad brakes as we don't (as of now) have a towed vehicle. But it would be a concern, obviously would not want the toad brakes to be activated unless service brakes are applied.
The attached seminar PDF from the folks at VMSpc provided me with an interesting perspective in regard to this topic. Probably relevant with or without VMSpc but certainly showing the advantages of having VMSpc data available.
I don't know if our coach is heavier than others but we had to manage things very carefully if we didn't want to build a lot of transmission heat. This means higher rpm and lower gears. One of the more annoying things about descending is that the maximum rpm off load (using the retarder) is a bit higher than maximum rpm under power. This means that if you ride down at a higher rpm, you have to continue to decelerate to get the engine to a safe speed to apply power, and you have to apply power before it will upshift. I mean lets be serious here, it's like a dream come true driving this vs other things I've driven. Just a minor nitpick.
We got passed by so many trucks and rvs down steep grades it made me wonder if I couldn't just pick it up to normal highway speed and be okay. When it said "truck speed 25mph". We did 25mph.
We also were fairly slow up the hills. I made sure to keep engine temps under 200F when I know the engine can take something like 220. For us, this actually meant pulling over and cooling off during our climb of echo summit, but never had to any other time.
That has always bugged me too.
jor
YES, most engines do have a higher RPM off load than governed RPM under load.
Here are numbers for a 2003 Cummins ISL:
Idle speed: 600-800. Peak Torque 1200 lb-ft @1300RPM. Peak HP (400) @2100. Governed RPM 2330. Overspeed 2600.
When descending above governed rpm, doesn't a tap on the throttle trigger an up shift? I seem to recall it doing so.
Two answers:
Whether you touch the throttle or not, when the RPM reaches "overspeed" it will upshift.
If you touch the throttle (even just barely touching it) the transmission will upshift even if well below governed RPM (think of it as a "normal light throttle upshift".
Looks like we have two threads going on this one. Anyhow, I use the tap the throttle method as I have always been afraid to let the engine wind up to the overspeed limit. Does anyone do that and just let the Allison upshift?
jor
On our trip down the West Coast from Washington State we used the retarder to slow for curves and down hills. Coming down the very steep and long pass in Death Valley I apparently let the retarder do too much of the work and got a trans hot red light. Downshifting did not really work so I just used the air brakes instead of the retarder and then took a break to let things cool down - the light wen out in less than a minute. No drama, smoke or anything like that and everything worked fine across the rest of the USA. The setup in our 36' 1997 U270 makes for a very good drivers machine with lots of feedback and control...this coming from a former tour bus driver in Alaska driving the robust MCI motorcoaches with 8V92 Detroits on some of the more challenging dirt highways in the USA.
I am with you, I initiate the up-shift. Think of the Allison's automatic upshift as the "fail-safe".
Tom and Ron [red tractor], I talked to Aubrey Lee [ex Foretravel Electrical guy] when at MOT this morning and he confirms you were right, and Foretravel did install a connection that activated the brake lights when the Joystick retarder became standard. He said they did it because DOT or some other gov. agency required it. I guess a PO disabled it on my coach. If anyone knows where this connection is, would appreciate the info. Would probably hook it up again, and install a switch so I could defeat it when necessary.
I'd look in the schematics. I suspect you will find a relay.
All of the above would seem appropriate!!
Change down, use retarder, use brakes if needed. With retarder selected the brake force is multiplied when you use them.
My brake lights do come on when the joystick is pulled back. 2001 40ft U320 Build #5865.
But, remember, if the transmission gets too hot it will give the alarm, and eventually shut the motor off!! Not good if you have more downhill mountain in front of you!!!!!!!!!!!!
Speedbird 1.
Nothing in my schematics, only shows relay activated by air brake pressure switch. Can you post yours? thanks
For those with retarder overheating issues, remember that if you are using only the joystick controller to slow you and not your service brake [pedal], and your toad uses your service brake air for its braking, like my M&G, your retarder now has to dissipate the heat generated by slowing down not just the coach, but the toad also.
If your retarder is overheating using the service brakes will make it worse. Adding another notch will only make it worse. The only way to increase retarder and transmission cooling (and engine cooling) is to increase RPMs. Reduce speed, downshift, use one or two notches of retarder. Minimize service brake use to just deliberately reducing speed. If that is still too fast slow down more and downshift again.
It is entirely up to you to establish and maintain a safe and comfortable speed and stay in control. If the speed limit for a curve says 40 mph for example then you should consider that an absolute maximum speed.
Yes. As Roger states. Use the service brakes to reduce speed so you can downshift, then get off the service brakes. After downshifting
, you can maintain your speed with less retarder.
"If your retarder is overheating, using the service brake will make it worse"
Not if you turn off your retarder and use a combination of transmission gearing and service brake, use till transmission oil temps lower.
Using your service brake allows the toad braking system to work, reducing load on your coach brakes. Not sure about yours, but my transmission oil cools way faster with retarder off completely.
Truckers drove for many years without retarders, jakes or pac brakes. using just service brakes and gears.
And truck run away ramps. There was always tire tracks in the one on the Grapevine north bound back in the day. The drums would expand with the heat and with just a 2" stroke on the air cans the brakes failed.
Yes took my 4905 through the mountains several times. 3 speed auto, drum brakes, no jake. A lot of 1st gear driving.
Did keep an eye out for the runaway truck ramps.
If you have a retarder why wouldn't you use it to your advantage. The service brakes use a much higher retarder load when the retarder is on than one or two notches of the joy stick. And overheated service brakes don't do much of anything when you are headed up the runaway ramps. The retarder temperature and transmission temperature change at dramatically different rates when the retarder is on and in use. They are both cooled in the same transmission fluid heat exchanger to the engine coolant. The only way they are cooled faster is by increasing RPM to reduce engine coolant temps and the rate of cooling.
Slow down, use a lower gear, use some retarder, increase RPMs, use limited service brakes. Seems to work for me and many others. We have come down long steep grades at appropriate speeds always in control and rarely exceeding 235° retarder temps while transmission temps will be about 190-195 and coolant temps about 180-185.
Or do whatever you want.
We use a ReadyBrute towing system that is independent of both the retarder and the service brakes. The toad brakes come on proportionally to the difference in speed between the coach and the toad. If the coach is slowing down for any reason faster than the toad the toad brakes are on. No impact on retarder or transmission temps.
Another good thread on transmission temps. high transmission sump temperature? (http://www.foreforums.com/index.php?topic=20903.0) Transmission Retarder Operation - How Does It Work (http://beamalarm.com/Documents/transmission_retarder_operation.html)
I am a firm believer in using the retarder to its full ability, just pointing out what to look for if your temps are high.
Tom, rechecked all my diagrams, can not find it. As you are one of the few people on the Forum that has a 2003 like me, would sure appreciate you sending me a pic of the schematic, or at least a reference to it.
Thanx. Jim
I believe it is in the center of this diagram.
Thanks Tom, I have that one also. Just need to decipher it and find the actual parts.
UPDATE:
We finally had a chance to make practical use of knowledge gained. In our trip from Clayton, NM to Eagle Nest, NM (details in "2018 Inaugural Journey" post) we crossed Raton Pass (7834 elevation) and Bobcat Pass (9820 elevation). Grades up to 8%.
It boiled down to these learnings for us towing our 4 door Wrangler packed for our 6 month trip with full fuel and water for dry camping.
1. Transmission downshifts are the first priority in climbing and descending. We found a general rule of thumb in our coach is that 2nd gear is good up to 30 mph, 3rd up to 40 mph and 4th up to 50 mph. This keeps our coach in 1800-2200 RPM which is the sweet spot for power and cooling. This meant the steepest climbs we're in 2nd or 3rd and the same for the steepest descents, especially with 25-35 mph posted speed corners. I used pullouts to let faster traffic through only when I could do so safely. Engine temps never got over 200 and tranny temps never above 210.
2. Retarder usage was limited since descent speed control was so well controlled with tranny gear selection. I used 1 click when approaching a 25 mph downhill corner from a 45 mph approach and only a couple of times 3 clicks when the corners came more quickly (and I was looking at scenery 😱).
Granted this was our first ascent/descent experiences and although grades were meaningful, there were no hairpin turns or switchbacks which I'm sure we'll discover at some point this year.
This was a confidence builder and I am quite comfortable with the up and down arrows as my friend. Only my observations from the seat of our 34', ISC 350. Your results may vary.
Good job.
You are no longer only a "FLAT LANDER".
And once you see all the west, bet you will put your FL brick and mortar up for sale.
Pierce
Mountain driving is a learning process. You have picked up the basics pretty well so more practice will improve how you do. The big yellow speed signs should be considered maximum speed around corners until you have much more experience with your coach.
My first few trips through the mountains were pretty experimental. Then with purpose. Most of them now are just enjoyable drives through the best of places feeling in control and safe.
Good job, Randy. Give yourself time to be safe. Wherever you get to, however long it takes, however far you get, doing it safely should be your first priority.
My 97's retarder works on cruise control and the brake lights come on when it's triggered.
Way easier to drive IF you do not mind the coach being tugged back down small grades.
I Flip the lever off if it tugs excessively
Reading this discussion reminds me of my initial confusion and concerns about how to use the retarder. Lots of conflicting advice. In practice, though, it turned out to be quite simple and pleasant with a feeling of confident control climbing and descending any grade in my 295. I'll add my points.
One pretty good piece of advice is to start your descent slow....using the lowest gear going down that you used coming up. Now, all you studs bragging about roaring uphill with your 320's can get caught by this, they're all equal going downhill, as a matter of fact my lighter coach has an advantage. So if you've really attacked the climb in, say, 4'th, you might want to punch in the number 3 before you start your descent.
You use your retarder to control RPM. You want the revs in the upper range of allowable. (You do know your RPM limits, right? This number varies vastly depending on which engine you have. You need to know this for sure.) This provides you with good retarder braking effort and lots of coolant circulating to keep the retarder temps in check. If your speed starts climbing and engine RPMs start approaching limits, dial in some more retarder. If, after doing so the retarder temps climb too high.....get on the service brakes, haul the speed down, and downshift a gear. Repeat process including adjusting retarder to maintain upper range of rpm. (You need to know what acceptable retarder temps are. Totally different from allowable engine temps, much higher.)
So, you are descending in a lower gear, managing your speed through a combination of gearing, retarder, service brakes. You are going down at a controllable pace, which gives you time to monitor two critical gauges. Tachometer and trans (retarder) temp. These are the biggies. Keep these things in range and it's all good. And keep an eye on the road, of course, but if you're descending a steep grade properly your speed is low enough for this to be almost secondary.
Start down slow, in a low gear.
Dial in retarder to manage RPM.
Adjust gear down if trans (retarder) temps climb too high or road speed is too high.
Don't be afraid to use your service brakes to adjust speed to reset gearing and retarder.
These coaches, with their all round disc brakes and retarder give you the tools to make descents of any grade not only comfortable but enjoyable. Develop your own technique, as others have said. I often pick a comfortable gear and then use retarder only from 0-6 clicks, backing off when the temp climbs. I like to feel it kick in....
I have noticed that the bigger displacement m11 seems to have a better hold back down grades than the smaller motors.
Especially if as Wolfe suggested here I downshift the motor to nearly full revs.
Engine/trans cooling serms to increase and less service brakes and retardation levels can be reduced.
I drove the coach at lower revs for the first 20k miles and noted the higher trans temps and heavier service brake use.
Revved harder as he mentioned does seem to be a better way to use the coaches displacement.
I drove n14 Cummins in Monaco's and the service brakes were hardly needed. 855 cu in inline 6 slowed it down very well
Right, though I always attributed the more powerful retarder on 320 to the 4 series Allison compared to the 3. That said they both have, I believe, the same cooling/radiator capacity which ultimately determines how much retarding you can do before the bell rings.
Bob....for the ISM/M11, of which you have experience and noted above about max rpm for cooling,
What should be the upper limit for the rpm purposely set by selecting gears to give the baking and cooling and at the same time not endangering the engine?
2,100 rpm. No load. Hard to hurt these downhill. Rev it.
Every owner was paranoid about their baby(coach)
Spent a lot of my time explaining that these were very sturdy and the rv use was very light duty
Roger.....and maybe Chuck too.....thanks for introducing the concept and concept that you do not want to apply service brakes while applying the retuard.
As I read you, the service brake activates higher levels of retarder than you probably wanted using the job stick and thus with the application of the brakes, bringing more retarder, the heating is more than you would expect. I think that was true in the mountains and I just did not make the connection that the braking gave more retarder than I needed. That leads to sort of a pumping the brakes/retarder regimen I think versus the smoother rpm approach.
At the same time, I am thinking the service brakes may be needed to activate the toad bikes? I wonder.
Anyway, rpm is the secret . Have been doing that but as Chuck wrote in a summary of the procedures to follow, the service brakes have their role to get you a different gear as needed.
Thanks guys. Cheers.....
Bob....thanks, again for your help.
I must say that I have been adverse to letting the engine go above about 1800. Every once it a while it will bounce up to the 2000-2100 range, which I thought was an absolute limit, and then quickly the system would adjust to less rpm without me doing anything.
Very interesting, makes thing easier if it is okay as you say.....let it rev going downhill. Every since getting our first diesel I have thought over- revving, which could happen by engine braking, and that would be a great threat to the engine
thanks...
I had to break in almost every used coach I took out rving.
Invariably they been babied. Slow. Lower revs. Less mpg
I have had customers ask me to take their brand new coaches out rving first. Less hassle for me to find things.
A couple of points.
Yes, the transmission is programmed to automatically upshift if RPM exceeds limits. I had never had that happen, and if this is occuring then you're doing something wrong, not in full control. You need to manage it so RPM overspeed is not achieved. Couple good reasons for that, the first being that when auto upshift occurs your downhill speed will increase. Another is that what if there's a glitch and your trans doesn't upshift? Then there is a real danger of serious damage to the engine. Kind of like not worrying about a fire because there's an automatic fire suppression system.
There are some coaches out there without a joystick controller for the retarder which is activated by the brake pedal only. These require a different approach, one which I am unfamiliar with.
Serivice brakes while the retarder is on....yes, hard braking (which is the technique to use to if a downshift is required, a firm, short duration service application) does increase retarder to max. Once again, preemptive management of your speed and temps means this is really not a factor. You should be getting on the brakes and dropping a gear before trans temp is in the critical zone. If you have, the extra retarder from brake application won't matter. If temps are critical range then get on the service brakes and back off the retarder while you brake and downshift. Management of these systems, is the key. Don't rely on fail safes built in.
The brake light activating the toad brakes is troublesome. Since you're using retarder for long period of times, if the retarder activates the brake lights, and the brake lights activate toad brakes......not good. Everyone knows that dragging brakes going downhill is bad technique and that's what the toad is doing. Might want to consider how to deal with this.
Preemptive management....picking a sufficiently low gear for start of descent....knowing your allowable RPM range....knowing your allowable retarder max temp....and balancing these factors is key. Worrying about traffic behind you and attempting a too high descent speed = bad decision.
Finally, I see people referring to Pac Brakes and Jake Brakes as retarders. Totally different systems, managed differently. In fact, these engine style brakes are easier to use...and in the case of Jakes, probably more effective than retarders.
Here's a link to the Allison manual for 3 and 4 series Lots of good info.
http://ddwt.us/Allisson_4000MH_Transmission_Owners_Manual.pdf
We have the Pac Brake and love it! Have pushed and pulled this steep I-17 run from Phoenix to Flagstaff many times. I activate the Pac just before the drop, let the Allison do it's thing and keep the speed waaaay down, hardly ever use the main brakes unless some idiot cuts in front! Have had many big coaches come blowing by us only to see the brake lights on the coach & toad come on HARD! I pretty much follow the 18-wheelers down, they've got the Jakes, much like our Pac.
Big trucks use Jakes as they have manual transmissions so no retarder possible. I have driven both retarders and Jakes. The retarders work well but require a more complex addition to the Allison transmission (read more expensive overhauls if tranny fails). While they are very effective, especially if used correctly, they heat the transmission fluid so have a limited time they can be used on long descents. I can't imagine this being a problem on interstate descents as they are never very steep so aerodynamic braking usually limits the speed.
The Jake or Jacobs Brake is very simple and turns the engine into a big compressor. Again, it has to be used properly as it works best at higher RPMs. They can be kept on all the time as they operates only when you take your foot off the accelerator. Outside noise is not a problem with the stock muffler on the U300 but might be in residential areas for coaches with a resonator.
I keep the Jake switch on all the time. In 4th gear (high gear), it has a subtle effect on interstate downhills, while steep two lane highway downgrades are easily descended in a lower gear and high engine RPM. Heading down the eastern or steep side of Donner Pass on I-80, I shift to 3rd (out of 4) and use the service brakes perhaps three times before reaching Truckee.
Both are braking aids to supplement the service brakes and should be used in a secondary function rather than for primary braking.
Pierce
What all is involved in upgrading from a single speed (switch) retarder and a joystick on the 3000 series Allison. I live outside of Denver and a lot of our trips involve a trip over the big HILL !!! Never felt like I had too much brakes in my coach. Thanks for all the info on this wonderful forum amazing what you can learn just from reading.
My bad. That should be from a switch to a joy stick thanks
tonka,
On your coach('96- 270) IIRC you should need the joy stick rheostat, the "Y" cable, and the interface module. I have the part numbers at home base but are on the road at present. I will hunt them up and post them for you. It is a plug & play system so the hardest thing is to take the switch pannel apart to mount the rheostat.
Mike
Reply #4
Joystick retarder control (http://www.foreforums.com/index.php?topic=5786.msg24049#msg24049)
So in everyone's opinion is it worth the upgrade
tonka,
You can call Ted Keating at his business TKT 800-997-4858 or email him at TKT Sales Allison Transmission Parts Supplier (https://www.allisontransmissionpart.com/index.php) he is a good fellow that will have the exact part numbers you need and should have them on the shelf for the best price. We have used him for years. He will be faster that waiting on us to get someone back at home base to look
up the info there.
Pamela & Mike
Sharing another day in the mountains. For those who've been there no need to read further...for those just starting read on.
First, any significant climb or descent is unlikely to be posted at more than 45 mph, with most 20-35 mph. So the first thing to remember is that you will not be going fast!
First, select a gear that will work as you climb. For our coach this is about 2nd gear to 30 mph and 3rd gear to 40 mph. Open the window and listen to the engine. I love our resonator because it "sings" from 2000 to 2200 rpm in the gears listed. This will work as you climb and as you descend.
On the descent I use the gears listed and 1-3 clicks of retarder IF needed to maintain posted speeds. Remember that joystick retarder only works when you are off the throttle. If you're in 3rd gear, for example, at say 40 mph and are heading into a 25 mph corner you only need to lift from the gas to have the retarder bring you back down to 25 mph with 3 clicks (at least in our coach). I rarely had to use the brake.
I routinely look for turnouts to let faster traffic pass rather than trying to increase my spe d to keep from holding them up. I'm retired and have n9 schedule to meet. Those behind me must have a schedule so Inlet them by as often as it's safe to do so. I never pull over unless 8s safe for me to do so.
I have NEVER had temps over 215 on the tranny using this method.
Remember I'm a newbie...others may be able to go faster. I'm only sharing for those who want to enjoy the mountains and not fear them.
Randy
Randy, if you have a VMSpc and can watch retarder temp it will be the important one to watch. They will get much higher than transmission temps very quickly. Good lessons learned so far. The right and correct speed up and down is what you are comfortable with. That will change with comfort level and experience.
Per Allison, the retarder temperature out is considered overheated when it reaches 330 degrees F. This is for Transynd. Does anyone know the recommended max operational temp of retarder?
Please note this is for the retarder, not transmission sump temp.
I have the VMSpc retarder yellow warning light come on at 235° and the red light come on at 250°. It is conservative but I can do long downhill grades at 6% in fourth gear and one or two notches of retarder and rarely exceed 235. It will go up with braking. If it gets to 250 I slow down, drop a gear. Interstate downhill grades are going to generally be pretty straight. Everything else seems to have a lot of 40 and 45 mph curves so that sets the general speed.
If you are much over 250 I think it is an unnecessary load on the transmission, slow down.
Here is an auto transmission temp/failure chart in the attachment.
Pierce
I took some long grades today driving from Lake Powell to Bryce. Easy peasy. Dropped it down two gears and retarded until I felt the downshift, then adjusted the retarder, usually off or first notch, for 45-50mph.
No vmspc, so watched the tach and felt for the downshift.
Dashboard trans temp never rose.
One of the advantages of a VMSpc is that you can see what happens when you change operating conditions. The retarder temps can change very quickly while transmission temps change slowly. Step firmly on the brakes with the retarder on and retarder temps can go from 190ish to 250 in 15 or 20 seconds.
Steady state speeds in 5th gear with 2 notches of retard vs 4th gear and one notch is a pretty big difference in retarder temp.
Drove mountains last several days. Here's my take.
If you're somewhere beautiful, the driver will want the flexibility of looking out the window occasionally. If your pushing to max speed for safe temps you'll be going faster than the speed the driver will enjoy. I've found that 20-45 mph will work on any of the ascents or descents we've encountered. For me that means 2nd gear up the most sever ascents at abou 30 mph or 3rd gear up 40-45 mph. Same on the downside of these severe descents but usually 2-3 clicks of manual retarder.
Haven't seen engine or transmission temps over 210...and even those for only a brief time.
Haven't had any interstate speed ascent/descent encounters yet...just the New Mexico, Utah National Park stuff..
I have read that the transmission retarder is setup to begin load shedding at 300 degrees. I don't go that high however. With transynd, 275 once in a while for short times wouldn't overly concern me. Of course lower is better.
Pierce's transmission failure chart
Transmission temperature/failure chart. (http://www.txchange.com/heatchrt.htm)
appears to be for organic transmission oil and for the mostly automotive and light to medium truck transmissions the Transmission Exchange deals with.
Maybe we should be looking for an Allison specific document.
So based on what has been said I am to understand that tapping the throttle above governed speed (but before overspeed) to initiate an upshift will not cause any harm? I thought I read somewhere that this is a bad idea. That is why I slowed down below governed speed before hitting the throttle to initiate upshift which is what annoyed me.
That has been my experience. Downhill with no throttle in say 4th gear and a notch or two of retarder. The hill starts to flatten out, gear range shifted up to 5 or 6. It needs to see an open throttle to shift up. May take more than just a tap. 1800-1900 rpms seems like and upper end to me.
Brett,
Of course I understand that applying throttle makes an upshift but I found as I have been doing this that it always takes a second or two under power before it upshifts. Intuitively my concern was that if I pressed the throttle above governed speed but well below the Allison forced upshift rpm (say 2250RPM) that the engine would actually get fuel and power above governed RPM which was bad (though I admit to being ignorant of which engine component can't deal with running above governed speed). If pressing the throttle above governed RPM doesn't actually give fuel and apply power then there would literally be no potential consequences to doing so and all these years of me slowing down below governed rpm before hitting the throttle was silly. That's what I'm wondering. I may overthink driving the thing but I'd rather err on the side of caution when I am moving 65 feet north of 40,000 pounds. Plus I'd prefer not to drop >$10K on an engine if I don't need to.
Mark,
The governed RPM is for the engine under load-- read that working HARD.
Touching the throttle enough to cause an upshift (say 5% throttle) is a non-issue.
On pulls, 7% and higher, I do keep a close eye of the gauges, but have never had to downshift, the Allison is one smart cookie!
On pushes, same deal, start slowly, hit the PacBrake and toggle it as needed, let the Allison decide. ^.^d
Thank you, that's very helpful info.
We bought our coach for a number of reasons. One was the safety of a diesel pusher with retarder in those CO mountain descents. I have not been disappointed and enjoy the ability to descend with both feet flat on the floor and only rare use of the service brake. The DW commented one time "You know you are going slow don't you?" To which I replied by pointing out the semi ahead of us doing the same thing.
One aspect of mountain driving I didn't really appreciate was the need to gear down on the climb to limit the transmission from up shifting and getting into too low of an RPM range. We were heading down to Boulder (having grown up in the midwest north is up, but in CO you have to balance up being north with going down in altitude....thus despite living south of Boulder, because it is lower in altitude it is down) on a hot July day I received an engine temp warning. Luckily I was at a spot where I could pull off into a business parking lot and let things cool down.
For those of you that have taken Hwy. 285 from Kenosha Pass (9,990') into the Denver metro area, you know that yes you descend 4,000+' but the highway has a large amount of ascents and descents. I failed to keep the RPM's high enough on the ascents to keep the engine cool. After reviewing this forum and the Allison manual I realized I needed to gear down to keep the RPM's within 500 of the governed limit (2,100 I believe).
When I got home I was talking with my neighbor who drives truck for the CO Department of Transportation and he said they have diesel trucks with Alison transmissions and they absolutely gear down when climbing Monarch Pass (~11,300') to keep the RPM's high and improve cooling.
Lesson learned!
It was fun to revisit this post from our trip out west last year. We learned a lot and here's my 2 cents. Yes, the retarder works. But I now use it less frequently.
Brett Wolfe, and others, taught me that engine RPM is my friend for braking and cooling. I've even learned it can help with gas mileage. On uphill grades I now downshift as needed to keep RPM above 1800. On our coach Cummins manual says peak power at 2000 RPM. Even moderate grades on the interstate with cruise on benefit from manual downshifting to maintain speed.
On downhill grades the "run the gear down that brought you up" works before considering the manual retarder. Periodic service brake use....firm and short...benefits from retarder activation from the service brake pressure and keeps tranny temps, especially retarder temps, moderate.
I'm not saying I don't use retarder, just that manual use hasn't served me as much as exercising engine RPM with manual get changes.
Remember, just my 2 cents.
Randy,
You are a diplomat. Yes, gear down going up to keep EGTs down, especially at higher altitude. Gear down coming down and remember, the retarder is a secondary braking device after both the service brakes and engine braking at higher RPMs.
Not my two cents, just the law of survival.
Tom, when you got that engine temp warning, imagine where the EGTs were at that time. Review the EGT video from a couple of weeks ago. This is why engines drop valves. Since the damage is cumulative, no one can say that they got away with overheating. I don't think twice about running up at the governed limit (2130 RPM) on the way up grades. Better to operate at hight RPM and use less throttle. I usually don't exceed 2000 on the down grades as I don't like to have to concentrate on not exceeding red line but the Jake usually does the job. In Colorado, the pass you describe is just the topography that can shorten a diesel engine's life. Remember measured altitude and density altitude can be several thousand feet different. The high temps and less dense air mean less efficiency for both radiator fan and the radiator itself. Again, less effective cooling, less power at altitude and not keeping RPM way up are the perfect storm for high EGTs. Mechanical diesels are even worse at high altitude.
Pierce
This is a great thread - I learned a lot after reviewing the last serval pages of the thread. I enjoy hearing from everybody's experience coupled with the science and mechanics behind the engine, trans, brakes, and vehicle weight. Thanks to all for posting. I will certainly use this info in my travels.
PB
I see this differently, here's why. I agree, the service brakes are the primary braking, but I would prefer to exhaust my secondary braking first before getting heavily into the service brakes. In practice, keeping RPMs up and retarder typically meet 95% of braking needs, (Rockies, Cascades, Bighorns) and an occasional stab on service brakes is used to keep RPM/retarder/speed functions within limits. I would hate to be in the position of having exhausted my service brakes and relying on the retarder to haul it down. Load shedding would be a problem....
Chuck,
That is not where I was going at all. Trucks and buses came with service brakes and gear boxes long before retarders came along. Using the gearbox/engine to keep speed under control is what professionals have been doing since they put diesels in trucks and buses. Too many RVers rely on the retarder to do most of the braking and have no real knowledge of how to use the service brakes in conjunction with the gearbox to keep downhill speed under control. So, when the yellow retarder light comes on, they don't have the knowledge or experience to know how to continue a safe decent. Sure, use the retarder but don't count on it to solve every grade decent encountered. I took many trips, in the Rockies with my old Greyhound. No retarder, just drum brakes and a Spicer gearbox. The grades never were a problem. Sure, I would have welcomed a retarder or Jake but I had experience on how to make the descents with only what I had. My point is many new (or old) drivers skipped the basics and see the retarder as the #1 braking system.
Same with the knowledge of altitude, temperature, barometer and humidity. Yes, even humidity. It's like learning to be a detective. Until you have this knowledge, you can't understand how the environment effects each and every trip you take. That's why the PO's driving habits can catch up to their old coach thousands of miles after they sold it.
It's no accident you see RVs pulled over part way up long grades. 90% of drivers can't really see the difference between driving their family SUV and the big rolling apartment they are behind the wheel of other than it's bigger and uses more fuel. Fortunately, this forum introduces the newbie to the safe operation of their pride and joy.
And to determine Density Altitude you really should have an altimeter, outside air temperature and an E6B to do the math. I have two out of three and I've experienced density altitude in an Ercoupe leaving Orange, MA in the summertime 2-up.
I've not used my E6B for ages but it brings back a lot of memories. With 85 hp, your Ercoupe needed lots of cool air if you were anywhere close to gross. I had a Emigh A-2 Trojan 8324H pictured in the link. emigh trojan for sale - Google Search (https://www.google.com/search?q=emigh+trojan+for+sale&tbm=isch&source=iu&ictx=1&fir=E6QOn3RjWjsyYM%253A%252CfYO2tDD026MhYM%252C_&vet=1&usg=AI4_-kRpNp-8a-OOrk1gSwXLU1NoEQilMQ&sa=X&ved=2ahUKEwi_ipW-zYzkAhUOna0KHem8CosQ9QEwAXoECAgQBg#imgrc=gxQ4p217CEzfhM:&vet=1) It had the same engine but the ribs on the outside of the wings. Really had to be careful out in the Mojave, especially in summer.
OK, you don't need your E6B any longer for most stuff. Here is a density altitude calculator much like the one I use. You first look at your GPS for the altitude, then you go to Windy: Wind map & weather forecast (http://www.windy.com) and zoom in to the state where you are. You make sure the "airport" on the bottom right is turned on and then just click on the closest airport. Up comes the info in terms used by airmen, but if you click on the airport, a left hand column comes up with everything in plain English. The humidity will be called the dew point and is in Celsius so you have to remember that when pugging in the values in the density altitude calculator: density altitude calculator (http://www.pilotfriend.com/pilot_resources/density.htm)
Pre-flighing an RV trip is almost as important as doing it for a flight, especially if extreme weather may be encountered. Heading across the Southwest, you can check the current winds with velocity and then use the slider at the bottom to see when they may weaken or stronger and which direction they are coming from. Several years ago, I posted photos of an RV and big rig on their sides within a few miles of each other. Same with temperature. Just a lot of information in an easy to understand visual presentation. So, Windy: Wind map & weather forecast (http://www.windy.com) or others like Ventusky - Wind, Rain and Temperature Maps (http://www.ventusky.com). I find windy is easier to check the local airports for info.