Transmission slipping, won't shift

[John L.]

Hello guys. I have a transmission problem and was hoping someone here can help me diagnose this problem. I have a 2005 2500HD D/A that is bone stock with 55K miles. I changed the transmission fluid and external filter two months ago and replaced it with Transynd using the hoot method. A couple weeks later I pulled the trailer to a race with my wife and son, unhooked the RV so my wife could run to the store and when she came back she stated that the check engine light came on and the engine was revving to almost 3k and there was no power and it wouldn't shift. She had to stop and sit awhile before the truck would run and shift again. I then pulled the trailer home and Bamm...the transmission made a loud noise and the tach went to 3k. I pulled over, turned the truck off for a few, started back up and was able to make the 5 mile drive home without incident. This happened again two weeks later while driving to Delaware and I had to do the stop and start thing several times just to make it there okay. It ran fine on the way home until I got to the FIVE mile long bay bridge in heavy traffic. I'm booking across the bridge on a slow incline and Bamm...it happened again. I had to slowly ease over to the slow lane and CRAWL up and over the bridge. I was afraid to stop the truck on the bridge in heavy traffic for fear of making the 10 o’clock news for causing a massive pileup so I continued to drive at 3k rpm's and NO power at all. I had DTC codes of P0700, P0731, P0732 & P0733 from an AutoZone scan and was wondering if either the Transynd or the hoot method may have caused these problems. Maybe during the transmission drain too much fluid came out before replacing it and starting the process over again to get it all out of the converter? I'm just seriously worried I did something wrong and hurt my tranny. My situation now does not allow me to pay to get this fixed so I'm wondering if I drive it easily until the funds are available whether this will damage it more. I would be truly grateful for any info/advise you all could provide for me.

Tia,

John

[Mark Rinker]

What you are describing sounds like 'Limp Mode' or a mode the Transmission Control Module (TCM) can set to protect the transmission from further slippage or damage. Its unusual to see this on 'bone stock' trucks that haven't seen power adders and/or excessively heavy loads being towed - which can cause premature clutch wear from overpowering or overloading the transmission, causing clutch damage from too much slippage and setting the limp mode to warn the operator of the problem.

How much does your race trailer weigh, full loaded? Have you ever seen extended, high transmission temps while towing it?

My only thought, short of a trip to the dealership, would be to 1) clear all codes that are set, 2) unhook both batteries for an hour, and 3) drive the truck normally letting the TCM 'relearn' its adapative shift points. (This is akin to hitting CTL/ALT/DEL on your computer - a 'reboot' of the ECM/TCM for lack of a better description.)

If the problem persists, its likely mechanical and I wouldn't drive the truck in this condition - as you see, its unsafe in traffic and could make matters even worse, increasing the cost of repairs.

Good luck!

[John L.]

Thank you for responding Mark. Sorry I haven’t replied sooner but I have been extremely busy. To answer your question my trailer weighs almost 11K fully loaded with bikes, fuel and water. I believe these trucks are rated for 12K with a 5'th wheel, so I don't think I have overweighed that capacity. I did replace the NBSU switch thinking that was the culprit, but that didn't fix it. Do you think that maybe from draining the trans fluid following the 'Hoot' method may have caused this? I'm just wondering if maybe I drained too much at one time before replacing it. I don't think I ran the truck longer then 5 seconds in drive during the change, but who knows. I may have become overly aggressive at getting every last drop swapped out of the TC. The funny thing is, the problem didn't appear until "after" I dropped off my trailer while my wife was riding to the store. I don't think the temps were over 180. Since, unfortunately It has happened while trailoring and that is my concern. When it did happen to me the temps were at 210-220. I thought with Transynd it would run cooler. Are the trans lines self bleeding? Maybe there is air in there from the flush? I did take it to the dealership and after having it for three days all they could tell me was that they never heard of Transynd and that that must be why the tranny was slipping! I lost all confidence in them after that. They are the same ones that wanted to charge me a 100 diagnostic fee for determining my intermediate steering shaft needed replacing. A quick call to Chevrolet solved that problem, but you see where I'm going. So,,to make a long story short I would love to be able to fix this somehow myself by getting a solution through these forums, or possibly get the name of a good, knowledgeable dealer who knows diesels, and Allisons in particular in Southern Maryland. Any and all advice would be greatly appreciated.

Thank you!

John

[More Power]

Three years ago I replaced the original Allison in Lil Red with an ATS Extreme. Before doing the swap I asked the guys at ATS what they recommended for the initial fill method and what to use for the ATF fluid (which was Dextron III/IV because the OE and aftermarket clutch media is designed to work with Dextron). They didn't recommend pre-filling the torque converter, so against my better judgement I didn't.

On startup, it set P0700 among others, though we had filled the trans with nearly 5 gallons of AFT before startup. Once filling the trans to the proper level, I reset the codes, and didn't see any more codes - then or since.

The point here is that a dry trans can and will circulate the fluid without doing anything special.

If you're servicing the transmission at the recommended intervals, and if there isn't any pre-existing damage, the normal service procedures as outlined in your owner's manual are all that's required to maintain the life and reliability of the transmission. A flush isn't required unless the transmission had been overheated (burned the fluid) or some sort of damage had already occurred.

In your case, I'd be inclined to drop the pan to look at the internal filter (screen) and oil pickup assy. The flushing process may have dislodged the assy, and it can't pull fluid like it needs to....

Jim

[John L.]

MP, very good advice, thank you. I did drop the pan after the drain just to inspect the internal filter. When I discovered how difficult it was to pull off I just left it alone. There were also MANY pieces I didn't expect to see, (switches, etc) and looked very complicated to I buttoned it back up and performed the fill without replacing the internal filter. The truck ran great afterward and it was only after dropping off my trailer after the first tow that it started, so there is a possibility I bumped something and will give it a second eyeball.

Are the clutch packs made differently for GM's Allison’s then one you would get directly for the vendor? If so maybe I shouldn't have used Transynd? Would you recommend I go back to Dex-III? I would hate loosing 160.00 bucks for nothing! Especially after reading so many posts from users that have made the change-over without problems. Have you heard of other problems with folks using Transynd?


Thanks!

[DmaxMaverick]

Transynd is Dex III fluid. It's Castrol's flavor of synthetic ATF, and happens to meet Allison's TES-295 rating for medium/heavy duty use (none of the ratings have anything to do with light truck use, BTW). I've never heard of any issues with this, or any other, fluid of the correct rating. Your problem lies elsewhere. Unless the fluid you bought is not what is labeled, or contaminated in some way, you can rule that out.

[WhiteTruck]

It is possible that you have an intermittent problem with one of the trans speed sensors. You will have to monitor these when the symptom occurs to be able to pinpoint it.

[John L.]

WT,

How would I monitor this? I took the RV to the track (5 miles away) and babied it along without incident. I was driving to work the other day unhooked and tried to pass a car,,,Wham, tachs to almost 3k and no shifting. I pulled over and turned it off, back on and I was fine (as long as I drove respectably). What would I look for in this case? Would I need some sort of gauge? I have yet to drop the tranny pan and take a look for something loose, clogged filter, etc. (lack of time). Maybe I can get to it this coming weekend. This is getting very frustrating..55K and 3 years old. This shouldn't be happening, and I feel chevrolet should warrant there product over three years/30K. Has anyone with the older powertrain warrantee received relief from their problems?
tia

John

[Mark Rinker]

Did you ever unhook batteries and do a re-learn as I suggested in the previous post? Is the SES illuminating when the limp modes are set?

I would try to get the truck to an Allison repair shop for diagnostics. Your problem is most likely a bad sensor, not clutches or related to the fluid change.

Figure out what is setting the limp, fix that problem...

[John L.]

Hello Mark,

Yes, I did unhook both batteries as you suggested for the 're-learn'. It didn't seem to have any affect however. :( Is the SES the same as the check engine light? I know that does come on immediatly afterward and only clears after it sits awhile..

If it comes down to it I will take it to Allison for a diagnostic. I'm sure they know these babies much better then the stealership. I was hoping i could get chevy to fix it under warrantee since it's only 3 years old, but they couldn't figure out what was wrong after having it for 4 days. Their recommended solution was to flush the Transynd out and replace it with DexIII dino fluid. Not a good solution in my eyes.

John