Intermitent Failure to shift into 5th Gear with Allison

[americanboy]

Please help if you have knowledge

I own a 2004.5 Crew Duramax with Edge/attitude. The other day I was coming home and at a cruising speed of 60 MPH in 5th gear/ with Torque conv engaged and I got that sudden urge to stretch the legs of the truck while I was on a straight away. I got the Truck up to just a little over 80 MPH and it shut down well before the Gov could shut it down. So being puzzled, I looked at my attitude monitor and it showed that my truck was in 4th gear without the torque conv engaged (thank god!) I limped it at around 60 MPH back to my house which was less than a mile and drove it to the garage. I noticed that the truck stayed in 4th gear even creeping into the garage. Once in position I put the truck in Park, and then put it in Reverse. The tranny stayed in 4th. I turned off the truck and restarted it. I placed the truck in Reverse and it backed up. The next day it drove fine with the service engine soon light on which disappeared a few days later.

Yesterday, less than a week from above situation, I was trying to get on the interstate and just before I was about ready to merge onto the interstate, I felt the truck hesitate and I looked and the truck was in 4th gear and the service engine soon light came back on. I pulled off at the next exit and turned my truck off and back on. Got back on the interstate with no problems other than the SES light.

Does anyone have any idea what may be wrong with my truck before I take it into the dealership and have them dig into it???

Not sure if this is related, but when the truck is cold the tranny makes smooth articulated shifts with aggressive power input. When the truck warms up, the tranny makes less positive shifts and the RPM's tend to tach out.

Truck has 85,000 miles on it and I am the second owner. Not sure if filter/oil has ever been changed???

thanks
Americanboy

[Mark Rinker]

Ummm...I hope that you are referring to the transmission filter/oil - and even then, thats not good. With that many miles, you might have a plugged filter. What does the fluid look like? Dark? Stinky?

Get it in to a qualified service center, or read here for how to properly do a complete transmission fluid service. Don't let anyone hook your Allision to a recharge/recycle type transmission fluid exchanger.

Your transmission is slipping at the high power settings and setting the code and limp. You might have glazed clutch surfaces, and certainly have worn out transmission fluid at this point. When cold, your clutches are holding better because the fluid is less viscuous and apply pressures are higher. As the fluid warms, it thins out, pressure drops, and clutch holding force diminishes.

[DmaxMaverick]

Sounds like a classic "Limp". You likely slipped the tranny or TC when you "stretched its legs" in OD. The SES will stay around for a while, even though the condition no longer exists. You will likely have a P0700 stored in the PCM, with a corresponding slippage code stored in the TCM. The SES will remain as long as the code remains in TCM memory. If this is the first time, take it as a warning to not repeat what you did. The stock tranny will protect itself, as long as you don't defeat the slippage alarm, which you can do with the Attitude.

Treat your tranny to a service, fluid and filter (your penance). Apologize and don't do that again. Very little chance you have caused any permanent damage. If you are nice to it, the SES will go away (as will the DTC) with a few warm up and start cycles.

[americanboy]

Thanks for the info guys, I was planning on getting the transmission oil changed soon, but now it looks like sooner. Hopefully that is all it needed. If not, I will keep everyone updated. Thanks