Using Jake Brake and long term damage on trans.

[tom chelbana]

Some RVers are saying that over the long run using your engine or exhaust brake can cause problems with your Allison trans from the down gearing. Was wondering from Tom what his thoughts are about brake use and Allison extra wear or long term damage to trans. One might also talk about engine long term extra wear by using engine/exhaust braking. ISM 500 with 4000 Allison.

[palehorse89]

Hi Tom, I am going to guess here that you mean this Tom http://www.irv2.com/forums/f125/form...eer-89293.html and if so you could PM him or ask in his thread he has going if he don't see your thread here. My opinion on your question, no harm will be done, a lot of big trucks have the same setup as these Coach's, garbage trucks for one, talk about a "proving ground" for something, not to mention our armed services and their equipment w/Allison's. Myself, I had a friend of mine(has the software and is a Allisom tech) reprogram (flash) my TCM (Transmission control module) so mine stays in 6th gear, no downshift to 4th,(but still downshifts right down to 1st according to speed) As I did not care for the "harsh downshift" all the time, and now if I need to I just downshift the transmission as I need to with a simple push of a button. At interstate speeds, 1800-1950 RPM's, gives me plenty of rpm's for my exhaust brake to hold my speed......I do not need my engine turning 2300 rpm's for my braking to work as others do.
Your ISM has a "compression" brake in the heads of your engine using the valves, no exhaust brake on yours I would guess....
Think of a big Cummins engine in a semi, now lets compare engine brake usage........you will never wear it out........or harm it.

[geezee1957]

I am a newbie. Just purchased a 2002 Mountain Aire with a 400 Cummins. It runs great and was well maintained by the previous owner. The coach now has 37k on it. My question is regarding the Allison and the jake brake. It seems at highway speed if I turn on the jake it immediately downshifts and winds up the motor to somewhere around 2300 (pretty much immediately downshifts to 5th) Is this normal, if so can it be changed. I would prefer it not shift down, or only shift when it will turn to a max of 2000. I guess I would like to use the jake to control downhill highway speeds rather than an abrupt stop, as it wants to do now. I also would rather not turn the engine above 2000. Thanks in advance for your advice!!

[Tony Lee]

Not going to hurt the engine to rev to 2300rpm.

There are a few options to make the auxiliary brakes a bit less "savage"

One is to change the default gear to 4 or 5, both of which aren't going to result in abrupt downshifts when you lift your foot at highway speeds.

Another option is to change the default gear upwards to say 4th and at the same time change the program to "latch" mode where nothing at all happens unless you lift your foot off the throttle and touch the brake. That way if you want to coast for a bit downhill, no braking will be applied unless you order it.

[Rich-n-Linda]

Our coach is built on the Freightliner XC-R chassis. It has the 400 hp Cummins ISL and the Allison 3000 6-speed transmission. This is a very common chassis-engine-transmission combination. The ISL has a true Jake Brake - a 2-stage compression brake - as opposed to an exhaust brake.

When using the Jake Brake, I found the braking action to be very aggressive. The Allison transmission is programmed to shift down to the next lower gear as soon as it can and not over-rev the engine in the next lower gear. It targets 2nd gear and will shift down all the way to 2nd as the speed drops. Those downshifts were dramatic and always caused a heavy braking surge as the downshift took place. That surge is hard on the drive train...and the passengers!

To say it another way, the Jake Brake is programmed to deliver 100% braking effort every time you use it. But there are times when less than 100% braking effort is desirable. Slowing for an interstate off-ramp, driving in stop and go 35 mph in surface street traffic or descending a gradual grade are all situations where the Jake Brake is useful, but not at 100% braking effort.

I took my coach to the local Allison transmission shop and had them reprogram the TCM to stay in 6th gear when the Jake Brake is energized. Now, instead of the computer controlling when the downshifts take place, I control the downshifts via the Allison transmission controller. The job took only 30 minutes and cost about $60. They connect a computer to the diagnostics port and make ONE change in the programming, changing "second" to "sixth" in the Jake Brake program.

What a huge difference! Now I can actually use the Jake in many situations where I previously could not. Depending on the gear I choose, the braking effort can be gentle or aggressive, as I need. Slowing for an interstate off-ramp is now a joy, using 5th gear in the slow-down. No more slamming into 4th gear at 45 mph! Driving in stop and go traffic at 35 mph in 4th gear provides just the right gentle braking effort needed to speed up and slow down with the traffic. I don't need to use the service brakes until it's time to actually stop.

If you do nothing with the shift controller, the transmission will still downshift to lower gears as you slow down, but it does so at much slower speeds than before. The end result is nice, gentle braking right down to 15 mph where the Jake disengages.

To those of you who claim that doing this will diminish the braking effort available in an emergency stop, you may have a small point. However, an emergency stop is an event lasting only a few seconds. From the time you hit the service brakes to the point where the Jake is providing meaningful braking effort is...a few seconds! By the time the Jake fully engages, the emergency is over.

If you are in the habit of placing your transmission in "D" and forgetting about it, then this mod may not be for you. I don't drive our coach that way. I take a more active role in driving over the road, and often use the transmission controller to choose the correct gear for the particular situation I am in at the moment. The computer is NOT always right in this application. It can't be...it cannot anticipate anything, it can only react to something that has already happened. You have eyes that can look ahead and see things that are about to happen. You CAN anticipate, whereas the computer cannot.

This was the best $60 I ever spent on our coach. In my opinion, they should come from the factory programmed this way.



Rich & Linda

[palehorse89]

Originally Posted by Rich-n-Linda

Our coach is built on the Freightliner XC-R chassis. It has the 400 hp Cummins ISL and the Allison 3000 6-speed transmission. This is a very common chassis-engine-transmission combination. The ISL has a true Jake Brake - a 2-stage compression brake - as opposed to an exhaust brake.

When using the Jake Brake, I found the braking action to be very aggressive. The Allison transmission is programmed to shift down to the next lower gear as soon as it can and not over-rev the engine in the next lower gear. It targets 2nd gear and will shift down all the way to 2nd as the speed drops. Those downshifts were dramatic and always caused a heavy braking surge as the downshift took place. That surge is hard on the drive train...and the passengers!

To say it another way, the Jake Brake is programmed to deliver 100% braking effort every time you use it. But there are times when less than 100% braking effort is desirable. Slowing for an interstate off-ramp, driving in stop and go 35 mph in surface street traffic or descending a gradual grade are all situations where the Jake Brake is useful, but not at 100% braking effort.

I took my coach to the local Allison transmission shop and had them reprogram the TCM to stay in 6th gear when the Jake Brake is energized. Now, instead of the computer controlling when the downshifts take place, I control the downshifts via the Allison transmission controller. The job took only 30 minutes and cost about $60. They connect a computer to the diagnostics port and make ONE change in the programming, changing "second" to "sixth" in the Jake Brake program.

What a huge difference! Now I can actually use the Jake in many situations where I previously could not. Depending on the gear I choose, the braking effort can be gentle or aggressive, as I need. Slowing for an interstate off-ramp is now a joy, using 5th gear in the slow-down. No more slamming into 4th gear at 45 mph! Driving in stop and go traffic at 35 mph in 4th gear provides just the right gentle braking effort needed to speed up and slow down with the traffic. I don't need to use the service brakes until it's time to actually stop.

If you do nothing with the shift controller, the transmission will still downshift to lower gears as you slow down, but it does so at much slower speeds than before. The end result is nice, gentle braking right down to 15 mph where the Jake disengages.

To those of you who claim that doing this will diminish the braking effort available in an emergency stop, you may have a small point. However, an emergency stop is an event lasting only a few seconds. From the time you hit the service brakes to the point where the Jake is providing meaningful braking effort is...a few seconds! By the time the Jake fully engages, the emergency is over.

If you are in the habit of placing your transmission in "D" and forgetting about it, then this mod may not be for you. I don't drive our coach that way. I take a more active role in driving over the road, and often use the transmission controller to choose the correct gear for the particular situation I am in at the moment. The computer is NOT always right in this application. It can't be...it cannot anticipate anything, it can only react to something that has already happened. You have eyes that can look ahead and see things that are about to happen. You CAN anticipate, whereas the computer cannot.

This was the best $60 I ever spent on our coach. In my opinion, they should come from the factory programmed this way.



Rich & Linda

I have been wondering if you ever had the reprograming done Rich after you posted a while back about this subject..........
I could not of wrote a better post than you did explaining the programing and no downshift, When I did mine, after words, the only regreat that I had..........was not doing it sooner
What a joy to drive and use the engine brake without the downshift

[hzjcm8]

Originally Posted by tom chelbana

Some RVers are saying that over the long run using your engine or exhaust brake can cause problems with your Allison trans from the down gearing. Was wondering from Tom what his thoughts are about brake use and Allison extra wear or long term damage to trans. One might also talk about engine long term extra wear by using engine/exhaust braking. ISM 500 with 4000 Allison.

No problem. The Allison will simply downshift and nothing will be affected. Allison retarders are much worse for heat generation and still no effect on the transmission. TES295 fluid will help to take any excess heat. Don't worry about it. Do an oil analysis on the fluid once a year.

[94-Newmar]

Perhaps Tom can chime in on this, but the sloppy, easy, no-jolt upshifts are actually harder on the transmission clutches than hard jolting up or downshifts. Sliding clutches = wear on the friction surfaces whereas harder shifts (more pump pressure) cause less wear and friction.

[hzjcm8]

It depends on road conditions and whether it's a close throttle , part throttle or wide open throttle downshift. Let's say you're climbing a steep grade at wide-open throttle. Under these conditions, the oncoming clutch, associated with the lower gear, sees more energy than a closed or part throttle downshift as you're slowing to a stop.