Transmission Problems

[JTodd]

My 96 k2500 has developed an odd problem. About 6 weeks ago, I had run errands most of a hot Saturday and coming off the interstate all was fine. Pulling away from the stop light, all of the sudden, when it got to the shift point at about 20mph it would shift into nothing. The engine would rev, but no gear. If I would keep the revs up, it would eventually shift into the next hire gear.

I checked the fluid - all good. It has not been changed in a while, but nearly all of the mileage is highway running nearly empty. It happened again that weekend after everything warmed up (30 minutes of driving). While cool all is perfectly fine. I crawled under and check electrical connections on the side of the trans. After disconnecting and reconnecting all seemed fine. Then yesterday it happened again, and again this morning. Both time after driving for a while.

Is there a sensor or something that might be getting stuck when it heats up? Between 6 weeks ago and last night everything was perfect - not a hint of issue.

Thanks for your help

[crashz]

I'm not familiar with the inner workings of the 4L80E, but have a little experience with its lighter counterpart the 4L60E and ancestor the TH400. In both cases the transmissions have a reverse band that is also used to lock a drum for forward gears. These tend to slip or just break. But usually it either works or it doesn't.

What it sounds like is that an acutator soleniod is not engaing, and that could be due to a few things. When warm, the hot fluid could be bypassing very worn or damaged acutator or accumulator piston rings (sometimes made of a sensitive plastic). Or like you mentioned, an electric soleniod is not doing its job. Any check engine codes?

Before driving it again, I'd pull the pan and inspect the fluid and anything thats collected at the bottom. This will tell you a lot. Obviously lots of clutch material, burnt smell, metal shards are all bad signs. Also if you have check engine light, get the codes. If its an internal electrical problem, that may be indicated in the codes.

Good luck and let us know what you find!
Leo