Community Forums

obbm · 04-20-2010, 02:45 PM

Had a hot right rear brake episode about two weeks ago. Cooled off and was useable. Consulted this forum where there were several suggestions to use the tranny to slow down and thus save the brakes.

I decided this might be a way to get home with still working brakes, so I tried using the tranny for slowing down. After all, it's an electronic/ intelligent tranny and won't let itself be damaged, right? WRONG,WRONG,WRONG.

Two days and 600 miles of tranny braking caused tranny BREAKING. The third gear clutch pack blew its brains out and took the tranny to tranny heaven. Sometimes the WH wouldn't even move. Sometimes it would. This WH chassis is a 2005 under a 2006 coach and at the time of the breakdown had 26,000 miles on it and had synthetic tranny fluid.

Fortunately we were 15 miles from Nashville where the best WH chassis service center is. Took it there and they quickly said take it to Allison warranty center 8 miles away.

Nashville is hilly and three times in the 8 miles we had to use the Suzuki XL-7 toad to push the WH up hills. A very knowledgeable Allison technician fixed it very quickly and under warranty.

I hope WH is really "trying" to fix this brake problem/failure/debacle/catastrophe/dumb engineering, as it could get expensive.

Brazel's RV Performance · 04-20-2010, 03:13 PM

Was this using the lever to downshift or using a GradeBrake?

obbm · 04-20-2010, 05:18 PM

Used the lever.

Insanity: doing the same thing over and over again and expecting different results.
Albert Einstein

Insanity: discussing the brake failure over and over again on this forum and expecting ANY results.
OBBM

max49 · 04-20-2010, 07:12 PM

Unfortunately, engine/ transmission braking is not 'Free'. I don't have a tran. temp. gauge but I've heard the tranny actually gets hotter holding the vehicle back than it does pulling it up a hill. If we could give up our automatcs and go back to stick shift, then you could make the argument that it might be almost free braking. If Allison was able to fix it that quick, it must have been a very minor problem, ???
Jon, I can't see how the 'grade brake' would be any easier on the transmission.
In fact, when I downshift mine, I always 'goose' the throttle a little to more closely synchronize the engine speed to the anticipated RPM at the downshift. I hope this at least helps the initial shock put on the tranny.

obbm · 04-20-2010, 08:22 PM

The third gear clutch pack was pretty much destroyed. The metal plates were badly scored and burned, and the friction plates were burned. Most of the time the WH wouldn't move at all when in gear.

Covington Power Services in Nashville has a very proficient transmission technician who spent two days and two hours rebuilding the transmission. Covington had the parts in stock. Allison covered the rebuild in warranty. Not my idea of a minor repair.

There seems to be a large difference between consumer service and industrial grade service. Covington Power Services is definitely at the top end of industrial grade service.

DriVer · 04-20-2010, 08:25 PM

Quote:

Originally Posted by max49

In fact, when I downshift mine, I always 'goose' the throttle a little to more closely synchronize the engine speed to the anticipated RPM at the downshift. I hope this at least helps the initial shock put on the tranny.

Max, I have an Ultrapower Grade Brake and you have to drive it to believe it. It's just as automatic going down gears as it is going up the gears. Unless you drive one you might not have a understanding about how it works. I think your over goosing by the way .. no such thing as trying to out think a 4L85E.

I'm on the road right now and the Grade Brake was working well today when it had to without any input from me other than just stepping on the brake to begin the sequence.

Grade Brake ... don't leave home without it!

Clonetrooper · 04-20-2010, 08:53 PM

I only used the trans brake once on my DP and turned it right back off. Transmission started warming a little and quietly protesting right away. I know you need braking power in mountains so think I'll rethink my route to the south even thought theres nothing wrong with my DP and it should be able to handle having the tranny brake on. I guess the exhaust retarder that is available aftermarket and most semis have would be useless because it is very obnoxious and not legal in many cities and also it would strain the tranny the same amount because it slows the engine thus the tranny. Most semis have standard trannies also. Will look into Grade Brake, thanks DriVer
Been the insanity route myself.
KC

max49 · 04-20-2010, 08:54 PM

I'm not over goosing Driver

. Did you forget I've been driving trucks since before they had synchronized transmissions. If you did'nt double clutch and match the engine speed to the gear , you either ground a pound or were coming to a stop.
So what is so special about the grade brake? The way I understand it, and tell me if I'm wrong; You hit the brake, it down shifts, you hit the brake it downshifts again. Is this right? If so, I don't have to hit the brake, I could just downshift but I choose to blip the throttle as I downshift. I can see how the grade brake may be nice for some who like as much done for them as possible, but for me , pulling the gearshift down one notch is not a big deal.
If I'm wrong on how it works , tell me please, because I very much like the 'engine brake' on the diesel trucks that I drive, but I think that comparison is apples and oranges.

sknight · 04-20-2010, 09:15 PM

From what you're describing something else took out that clutch pack, a trans has far more stress on it pulling than engine braking. If you don't believe me think about how fast you can get to 60, then how long it would take to coast down to a stop.

I'd suspect a pressure leak in that clutch pack either from a seal, incorrect clutch clearance or even a problem in the valve body or solenoid.

max49 · 04-20-2010, 09:15 PM

[QUOTE=DriVer; .. no such thing as trying to out think a 4L85E.

Yea right, just like the Allison, they'd have us going down 120 MPH right off the side of the mountain if we let them do the thinking for us.

dieselclacker · 04-20-2010, 09:29 PM

If the third gear clutch pack was pretty much destroyed by slippage as stated above, how do you relate this condition to using the transmission to retard vehicle speed? Once engaged with sufficient hydraulic pressure, the clutch pack is virtualy a solid connection. Sounds like maybe a pressure supply problem to the third gear clutch pack may be the problem. That clutch works just the same pulling or retarding. I use third gear regularly in my W-22 for both pulling and decending grades, and have not seen any appreciable change in transmission temperature on the scan gage. From my observations, the trans temp pretty well mirrors the engine water temp.

Dieselclacker

j griff · 04-20-2010, 10:20 PM

Dieselclacker,
When you say the trans temp pretty well mirrors the engine water temp - do you mean they are close to the same temp, or that they maintain the same relative temp, one to the other; i.e., water temp 200 & tranny 150; water temp 210 and tranny 160?? or both near the water temp of about 200??

Clonetrooper · 04-20-2010, 11:13 PM

Hey Max I like the obnoxious engine brake on many semis. I've held a Class A Hazmat Tanker license in Tex for work for over 12 years. Dont drive full size semis but truck/trailer (automatic thank god, left leg is 1" shorter from driving jamming jimmies before this truck) I use sometimes is just a little smaller. Seen a lot of cars move out of the center lane real quick (no trucks allowed in left lane on lots of highways so commercial traffic tends to drive in center lane and hope it moves fast) when a semi comes up and engine brake or jake brake decompressor sounds off. Wish I had one. Can't honk or tailgate if someone is on the phone or looking in the mirror in center lane, don't like complaint calls to my office.
Back to subject...I worry about the drive train on my DP because if I can't get her moving pretty quick I got my DW and kids to worry about. Both cars are Z71 Suburbans, don't like to tow cause they're a little heavy for my Discovery 38' .So I want to avoid a problem before it happens. Been around diesels a long time (30+ years)and Allison makes a hell of a forward/ reverse only marine gear for small diesels, mainly Detroit, up to about 600 hp range, but these RV trannies are not familiar to me. They don't seem to be bullit/fool proof but very good trannies all the same. The Cummings is a great engine so I don't worry about it stopping me.
Did a quick goggle after my last post and don't think Grade Brake would help me. Like I said my tranny did not seem to like being in retarder mode the one time I switched it on. Don't think there's a problem but if something breaks it'll be my fault. Don't like being stuck by the side of the road.
I don't want to roast my tranny going down a big grade. Train engines use their electric motor\brake unit to slow speed going down hill and they can generate a lot of heat doing this, kinda like you were saying about tranny getting hotter going downhill.
Probably enough said.
KC

DAN L · 04-21-2010, 03:11 AM

Quote:

Originally Posted by max49

Unfortunately, engine/ transmission braking is not 'Free'. I don't have a tran. temp. gauge but I've heard the tranny actually gets hotter holding the vehicle back than it does pulling it up a hill. If we could give up our automatcs and go back to stick shift, then you could make the argument that it might be almost free braking. If Allison was able to fix it that quick, it must have been a very minor problem, ???
Jon, I can't see how the 'grade brake' would be any easier on the transmission.
In fact, when I downshift mine, I always 'goose' the throttle a little to more closely synchronize the engine speed to the anticipated RPM at the downshift. I hope this at least helps the initial shock put on the tranny.

my understanding is that the ultrapower grade brake upgrade also locks up the torque converter while braking, while using the lever to downshift does not lock up the torque converter. that is one reason why transmission temperatures go up when descending hills without the grade brake upgrade.
i don't have the ultrapower grade brake yet, but i am considering it for this reason.