1994 GMC Transmission problem.

New here and was hoping someone had the same problem down the line, Its a 4 speed automatic electronic w/od , 5.7 engine, Tranny works great till it warms up and it completely goes out, Let it get cold and you can drive 10 more miles till it quits. No Slipping what so ever till warm, Ive been my own mechanic for many years and not familiar with electronic transmissions, I been told everything from converter to bands and pumps but in my experience usually they slip etc...When there cold not warm, Any suggestions would be appriciated......

 

Have you inspected your trans fluid? Does it smell burnt or look real dirty? Level?

Are you sure it's the tranny and not the motor?

 

Nope Nice and clean, Motor has about 5000 miles since total rebuilt....

 

How is the shifting? Does it clunk or jerk when switching into gears or while driving?

 

When its cold runs like there's not a problem at all, Till ya get about 10 miles on her...

 

Sounds to me like you have a bad lip seal.Sometimes the lip will come complely off the seal causing complete failure.When just a small peice starts coming off,it will run fine while cold while fluid is thick and then will blow by or through the slit when the fluid thins out because warm.

 

Check codes. GM OBD-I are real easy to pull up and tranny codes will not light the check engine light. They'll be two-digit codes in the 70's and 80's as I recall. If your tranny isn't the same one in my wrecker (4L80E), it's probably pretty close. When it failed after about 300k miles, it first started losing 4th gear when warm, but I've also run into tranny problems very similar to yours that were caused by a problem with a wire bundle, so a simple frayed wire could even be the problem. Trouble is, tracking it down can be a nightmare. Tranny working cold, but going squirrelly when warm is fairly common.

How many miles on the tranny?

 

Hey thanks for the replys, 156000 on tranny, Just what I want to hear check more electric, Been a diaster all winter for wiring....{Trucks, House, car}

 

A friend of mine had a truck like that. He went through all kinds of electrical fun with his tranny.