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 #75 – June 04, 2018, 12:22:42 am

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.

Re: Downhill Speed Control - Proper Gear Selection vs Retarder

Reply #76 – June 04, 2018, 08:03:35 am

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

Re: Downhill Speed Control - Proper Gear Selection vs Retarder

Reply #77 – June 04, 2018, 09:10:08 am

Quote from: Chuck Pearson – June 04, 2018, 08:03:35 am

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.

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.

Re: Downhill Speed Control - Proper Gear Selection vs Retarder

Reply #78 – June 04, 2018, 11:57:26 am

Quote from: Chuck Pearson – June 04, 2018, 08:03:35 am

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.

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

Re: Downhill Speed Control - Proper Gear Selection vs Retarder

Reply #79 – June 04, 2018, 12:23:44 pm

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.

Re: Downhill Speed Control - Proper Gear Selection vs Retarder

Reply #80 – June 04, 2018, 12:25:19 pm

My bad. That should be from a switch to a joy stick thanks

Re: Downhill Speed Control - Proper Gear Selection vs Retarder

Reply #81 – June 04, 2018, 12:33:16 pm

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

Re: Downhill Speed Control - Proper Gear Selection vs Retarder

Reply #82 – June 04, 2018, 12:34:31 pm

Reply #4
Joystick retarder control

Re: Downhill Speed Control - Proper Gear Selection vs Retarder

Reply #83 – June 04, 2018, 12:36:32 pm

So in everyone's opinion is it worth the upgrade

Re: Downhill Speed Control - Proper Gear Selection vs Retarder

Reply #84 – June 04, 2018, 12:42:58 pm

Quote from: tonka – June 04, 2018, 12:36:32 pm

So in everyone's opinion is it worth the upgrade

Yes

Mike

Re: Downhill Speed Control - Proper Gear Selection vs Retarder

Reply #85 – June 04, 2018, 12:56:55 pm

tonka,

You can call Ted Keating at his business TKT 800-997-4858 or email him at TKT Sales Allison Transmission Parts Supplier 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

Re: Downhill Speed Control - Proper Gear Selection vs Retarder

Reply #86 – June 08, 2018, 08:24:26 pm

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

Re: Downhill Speed Control - Proper Gear Selection vs Retarder

Reply #87 – June 08, 2018, 08:49:50 pm

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.

Re: Downhill Speed Control - Proper Gear Selection vs Retarder

Reply #88 – June 11, 2018, 08:53:52 am

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.

Re: Downhill Speed Control - Proper Gear Selection vs Retarder

Reply #89 – June 11, 2018, 06:41:54 pm

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.

Re: Downhill Speed Control - Proper Gear Selection vs Retarder

Reply #90 – June 11, 2018, 07:00:47 pm

Here is an auto transmission temp/failure chart in the attachment.

Pierce

Re: Downhill Speed Control - Proper Gear Selection vs Retarder

Reply #91 – June 11, 2018, 07:01:13 pm

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.

Re: Downhill Speed Control - Proper Gear Selection vs Retarder

Reply #92 – June 11, 2018, 07:38:29 pm

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.

Re: Downhill Speed Control - Proper Gear Selection vs Retarder

Reply #93 – June 11, 2018, 08:58:54 pm

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..

Re: Downhill Speed Control - Proper Gear Selection vs Retarder

Reply #94 – June 11, 2018, 09:02:06 pm

Quote from: Chuck Pearson – June 11, 2018, 08:53:52 am

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 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.

Re: Downhill Speed Control - Proper Gear Selection vs Retarder

Reply #95 – June 11, 2018, 09:09:45 pm

Pierce's transmission failure chart
Transmission temperature/failure chart.
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.

Re: Downhill Speed Control - Proper Gear Selection vs Retarder

Reply #96 – July 04, 2018, 12:25:16 am

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.

Re: Downhill Speed Control - Proper Gear Selection vs Retarder

Reply #97 – July 04, 2018, 07:59:52 am

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.

Re: Downhill Speed Control - Proper Gear Selection vs Retarder

Reply #98 – July 04, 2018, 08:53:53 am

Quote from: Mark D – July 04, 2018, 12:25:16 am

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? THAT IS CORRECT. TO INITIATE AN UP SHIFT, JUST BARELY GET INTO THE THROTTLE. AND IF SPEED/ENGINE RPM CONTINUED TO BUILD, IT WOULD DO THIS AUTOMATICALLY WHEN YOU REACH OVERSPEED.

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. SORRY, I DON'T UNDERSTAND. UPSHIFTING LOWERS ENGINE RPM.

Re: Downhill Speed Control - Proper Gear Selection vs Retarder

Reply #99 – July 04, 2018, 10:24:20 am

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.

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