Allison transmission acting strange

tbyrne · January 17, 2004

The transmission on my HD has been acting a little strange lately. It pretty much drives normal except when I come to a stop and then at times when I slow down to about 15-20 MPH and then accelerate. The best way to describe it is the transmission feels like it's catching up when I come to a stop.

I'll get down to about 5-10 MPH when the tranny will hit hard from 2nd to 1st. Sometimes it feels like it's quickly coming down from 3rd to 2nd and then bangs into 1st gear. The first time this happened I looked in the mirror expecting to see that someone had driven under the back of the truck. I can even hear the ABS humming because the truck is being pushed after it's almost to a stop. Another thing is I can slow down to about 15-20 MPH to coast around a corner then I'll lightly roll into the throttle to accelerate. It will feel like it's in neutral for a second or two and then bang into that gear. That's kind of fun when it happens while I'm going around a corner in the snow

There were two things that were done around the time that this started going on. The first was I started using Wester's programming and I replaced the fluid with synthetic. I changed computers again a few days ago but the problem persists. I've never heard of this happening with synthetic fluid so I don't think this is the cause put I'd like to eliminate all possibilities before bring it into an Allison dealer.

Any suggestions?

Thanks,

Tom

2002 8.1 Silverado HD - Comp Cam, TOGs headers, Volant induction, Direct Hits ignition, 8" lift 18" wheels/tires + more

2002 8.1 Suburban -Intercooled Whipple supercharger, TOGs headers, Volant induction, 22" wheels/tires + more - 407hp/558 ft-lb torque at the rear wheels.

Butch 02 Denali · January 17, 2004

Since you tried swapping PCM's Tom obviously that isn't the problem. Give Lyndon a call anyway though, I know he does programming for the Allison and maybe he can steer you in the right direction. If I'm not mistaken, I think the Allison has a seperate computer, not in the PCM.

Butch 02 Sierra Denali

tmf6902 · January 17, 2004

It's not your PCM...because it always happened to mine (sort of). It only happens at a certain temp, and doesn't do it all the time, so I havn't been to the stealer for it, because it's a totally random occurance. Mine seems to do it, when the tranny is warming up, but not to full temp yet. and it happens when I am slowing down to stop around 10-15 mph....it thumps down to 1st and the ABS kicks in, for about half a second......Can you feel your ABS in your brake pedal, because I can feel mine kicking back at me. I'm not really concerned because it happens maybe once every month or two....I've search for service bullitens but I can't find any complaints.....kinda happy though, I know I'm not crazy....I so have to say that it didn't happen till I got my bigger tires, so I figure it's just a hiccup in the computer????? And since the stealer hates it when you modify THEIR precious truck....ehh I just live with it. wen it does it every once in a while.....ok I'm done rambling

EDIT---I need to learn how to spell...or type better

Shaners · January 17, 2004

I would think it is a problem with the TCM or the Ally itself. Most likely the dealer will blame it on the larger tires...

The PCM most likely talks to the TCM, but since you tried both computers, I would say the problem lies elsewhere.

tbyrne · January 17, 2004

I talked to Lyndon about this so he put together another program with a few different settings. That didn't change anything. I drove the truck for about 45-50 miles today and tried to pin point exactly when it happens but I still haven't been able to do it. It seems like the tranny will bang into first more when I'm driving it hard. Like if I come up to a stop sign and slow down pretty quick. I can usually count on it hitting hard into 1st at that point. But then there are other times when I gradually slow to a stop and it will still hit hard. But then there are times when it will just down shift like normal.

I had to tow by buddy's Ford truck a few days ago (isn't that how it's supposed to be? ). The tranny shifted normal the entire time the trailor was connected.

it thumps down to 1st and the ABS kicks in, for about half a second......Can you feel your ABS in your brake pedal, because I can feel mine kicking back at me

I sure can! At least I'm not the only one that this happens to but now we need to figure out why it's happening and how to correct it.

Shaners · January 18, 2004

Tom, I know your truck is an '02 but did you read this stuff on Lyndons site?

Adaptive Control Feature of Allison 1000 Transmission

The transmission control module (TCM) modulates the current to both A & B shift solenoids, which translates to a proportional level of pressure to the clutch. In order to make a shift, the TCM uses software and calibration settings of several program parameters to determine the level of current sent to the respective "trim" solenoids. These parameters are referred to as "adaptive values"--with a new transmission and TCM calibration, the adaptives are set to a base calibration level. The transmission uses the base calibration to perform the first of each type of shift. However, once it has performed a shift, the TCM evaluates the actual shift and compares it to an "ideal" shift in memory. Based on that comparison, the TCM changes the settings of the adaptive values to a level that it believes will result in a shift closer to the ideal shift the next time it makes that type of shift. This is referred to as adaptive shifting.

When the transmision/TCM calibration is new, the TCM is in "fast adaptive mode". Relatively large changes in adaptive values take place after each shift. Once the TCM has determined that a given shift is close to its' ideal level, it switches to slow adaptive mode. In slow mode, the TCM is still evaluating shifts and changing values, but in smaller increments. When a shift switches from fast to slow, it is said to have converged. The TCM is programmed to try switch from fast to slow mode in as many as 15-20 shifts. It is important to realize there are many different distinct shifts recognized by the TCM, and each of these have it's own adaptive values. There are upshifts and downshifts to and from each range (1-2, 2-3, 3-4, 4-5 and TCC) as well as adaptives for each throttle load. The main point is that it may take a significant amount of time before most of the shifts converge from fast to slow adaptive, and thus it is not unusual to experience somewhat harsh or unpleasant shift quality until these shifts have adapted.

*If you are experiencing harsh shifts, it is important to verify whether shifts have converged (Tech2). If not, the TCM is still learning how to adapt that shift and simply needs to be driven a bit more with the intention of actually re-performing that exact shift complaint.

*If a particular shift is converged, yet still objectionable--using a Tech2, reset the adaptive values for that shift back to base calibration level. This will automatically reset the TCM to fast adaptive mode. The vehicle must be again driven significantly to relearn the shift. It is possible to reset individual shifts without affecting other shifts with the Tech2.

I'm sure you did as you have talked to Lynodon about this problem...

I still think it's a problem with the TCM or the Ally itself...

Cold weather with sloppy roads tends to bring a light throttle respnonse from your right foot, and if you've been running your truck fairly hard then it will take some time to "relearn" you're new driving styles under slippery conditions. You can force the tranny into a "quick learn" if you follow Lyndons indtructions.

tbyrne · January 18, 2004

I didn't see that. Thanks for the info!

I'm sure you did as you have talked to Lynodon about this problem...

Lyndon didn't mention this when I talked to him. I'll have to give him a call tomorrow.

I still think it's a problem with the TCM or the Ally itself...

Same here. I'm leaning towards the TCM because it started doing this after I swapped computer but it doesn't do it all of the time. I'd expect it to happen all the time if it was mechanical.

Cold weather with sloppy roads tends to bring a light throttle respnonse from your right foot,

Not mine We haven't had to much snow up here lately. I think there was only one storm since I did the origional swap last month.

and if you've been running your truck fairly hard then it will take some time to "relearn" you're new driving styles under slippery conditions. You can force the tranny into a "quick learn" if you follow Lyndons indtructions.

My driving tends to be mixed. Some times "normal" driving (not run to hard) but I usually don't have enough time in the day to do what I need so there are other times when I'm laying into it a little harder.

Resetting the values and driving something else when I'm in a hurry might help this relearn a smooth callibration.

Shaners · January 18, 2004

The adaptive control feature refers to the '01 models (according to the Westers site), but maybe Lyndon can shed some light on it if you call him....

tbyrne · January 22, 2004

I was able to come up with a list of possbile recall/service info for the Allision. It looks like 3 of them covers my problem -

18 - #PI00420 - LCT1000 8.1 L18 ABS Activates during harsh 3-2, 2-1 downshift and harsh garge shifts (8/20/02)

19 #PI00029 LCT1000 M74 Neatral feel/flare at stop (6/18/02)

This is what you refered to above -

15 - #02-07-30-032A info - Allision transmission control module fast learn proceedure update required after transmission repairs (11/06/02)

tmf6902 · January 22, 2004

If you goto the dealer with this problem lemme know what happens. it should be a warrented fix, right? This won't screw up Westers stuff will it? It should only affect the TCM.

tbyrne · January 22, 2004

I'm going to make sure they only change the TCM.

timk49 · January 23, 2004

thanks Shanners . I just learned a lot aabout the

Ally with that post

High Mileage · January 24, 2004

I've recently been experiencing the identical problems with my completely stock 2003 dually. To me it is obvious that the TCM is not recognizing the signal from the brake pedal correctly. Instead of the torque converter unlocking and basically going into drift mode it is going into a hold-gear mode. This is strange because I've had very little luck when deliberatly taping the brake to get the transmission to downshift and decellerate the truck, as it should.

Another thing, this happened only once, but is quite unsetteling, is that I was under mid-to-hard accelleration pulling into traffic and the trans acted as if it had gone into neutral between the 2nd to 3rd shift. I had to let back off the accellerator and hit it again. Makes a person worry about pulling out into traffic. Luckily I hadn't pulled out into a tighter situation where this failure would have relyed on the driver behind me to get on his brake. I don't think he could have been expected to react in time.

I'm taking mine in for service as soon as I get my Bronco back from the shop. Hopefully they will be able to pull up a history and diagnose the problem.

Concern is that I'm either going to get myself run over merging with traffic or come to a stop light, hit the brakes and have the trans drive me through a stopped vehicle. I DON'T LIKE EITHER OF THOSE SCENARIOS!

tbyrne · January 25, 2004

My truck is going into the dealer on Tuesday so they can check it out and reflash the TCM. I think this will take care of everything.

I haven't experienced the neutral feeling while accellerating but have had this while coasting around a corner and then rolling into the throttle. The truck reved like it was in neutral and the banged into gear.