Downhill Speed Control - Proper Gear Selection vs Retarder

Topic: Downhill Speed Control - Proper Gear Selection vs Retarder (Read 5141 times) previous topic - next topic

Re: Downhill Speed Control - Proper Gear Selection vs Retarder

Reply #50 – May 07, 2018, 04:58:51 pm

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.

Re: Downhill Speed Control - Proper Gear Selection vs Retarder

Reply #51 – May 07, 2018, 05:35:32 pm

Quote from: Tom Lang – May 07, 2018, 04:47:34 pm

I'd look in the schematics. I suspect you will find a relay.

Nothing in my schematics, only shows relay activated by air brake pressure switch. Can you post yours? thanks

Re: Downhill Speed Control - Proper Gear Selection vs Retarder

Reply #52 – May 08, 2018, 02:06:22 pm

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.

Re: Downhill Speed Control - Proper Gear Selection vs Retarder

Reply #53 – May 08, 2018, 03:19:13 pm

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.

Re: Downhill Speed Control - Proper Gear Selection vs Retarder

Reply #54 – May 08, 2018, 03:54:33 pm

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.

Re: Downhill Speed Control - Proper Gear Selection vs Retarder

Reply #55 – May 08, 2018, 03:57:04 pm

"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.

Re: Downhill Speed Control - Proper Gear Selection vs Retarder

Reply #56 – May 08, 2018, 03:59:42 pm

Quote from: jcus – May 08, 2018, 03:57:04 pm

"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 without retarder 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.

Re: Downhill Speed Control - Proper Gear Selection vs Retarder

Reply #57 – May 08, 2018, 04:09:57 pm

Quote from: craneman – May 08, 2018, 03:59:42 pm

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.

Re: Downhill Speed Control - Proper Gear Selection vs Retarder

Reply #58 – May 08, 2018, 07:01:34 pm

Quote from: jcus – May 08, 2018, 03:57:04 pm

"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.

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.

Re: Downhill Speed Control - Proper Gear Selection vs Retarder

Reply #59 – May 08, 2018, 07:15:01 pm

Another good thread on transmission temps. high transmission sump temperature? Transmission Retarder Operation - How Does It Work
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.

Re: Downhill Speed Control - Proper Gear Selection vs Retarder

Reply #60 – May 08, 2018, 09:45:06 pm

Quote from: Tom Lang – May 07, 2018, 04:47:34 pm

I'd look in the schematics. I suspect you will find a relay.

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

Re: Downhill Speed Control - Proper Gear Selection vs Retarder

Reply #61 – May 09, 2018, 10:42:00 am

Quote from: jcus – May 08, 2018, 09:45:06 pm

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.

Re: Downhill Speed Control - Proper Gear Selection vs Retarder

Reply #62 – May 09, 2018, 10:52:26 am

Quote from: Tom Lang – May 09, 2018, 10:42:00 am

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.

Re: Downhill Speed Control - Proper Gear Selection vs Retarder

Reply #63 – June 03, 2018, 09:09:46 am

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.

Re: Downhill Speed Control - Proper Gear Selection vs Retarder

Reply #64 – June 03, 2018, 06:42:08 pm

Good job.

You are no longer only a "FLAT LANDER".

Re: Downhill Speed Control - Proper Gear Selection vs Retarder

Reply #65 – June 03, 2018, 06:47:24 pm

And once you see all the west, bet you will put your FL brick and mortar up for sale.

Pierce

Re: Downhill Speed Control - Proper Gear Selection vs Retarder

Reply #66 – June 03, 2018, 08:45:17 pm

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.

Re: Downhill Speed Control - Proper Gear Selection vs Retarder

Reply #67 – June 03, 2018, 10:32:08 pm

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

Re: Downhill Speed Control - Proper Gear Selection vs Retarder

Reply #68 – June 03, 2018, 10:53:27 pm

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....

Re: Downhill Speed Control - Proper Gear Selection vs Retarder

Reply #69 – June 03, 2018, 11:14:01 pm

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

Re: Downhill Speed Control - Proper Gear Selection vs Retarder

Reply #70 – June 03, 2018, 11:30:07 pm

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.

Re: Downhill Speed Control - Proper Gear Selection vs Retarder

Reply #71 – June 03, 2018, 11:52:01 pm

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?

Re: Downhill Speed Control - Proper Gear Selection vs Retarder

Reply #72 – June 03, 2018, 11:56:42 pm

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

Re: Downhill Speed Control - Proper Gear Selection vs Retarder

Reply #73 – June 04, 2018, 12:00:07 am

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.....

Re: Downhill Speed Control - Proper Gear Selection vs Retarder

Reply #74 – June 04, 2018, 12:04:18 am

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...

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