Tranny Problem

[normanby]

I have a 1997 GMC 2500 4X4 diesel, built in Nov 1996. Recently my tranny has been acting up. It seems to be fine on flat roads but when going up hill at highway speeds it seems to come out of gear when kicking down. It only happens when in drive, 1,2 & 3 are fine. Also the gear indicator light sometimes doesn't work in drive. Sometimes only works in PN31. Any ideas? I live in the northern Yukon and don't have easy access to scanning tools.

Pete.

[damork]

normanby,
Your statement about the indicator light not working tells me your power supply to the "E" pin in the transmission (if it is a 4L80E) is being lost. This is not real common, but does happen.

Most of the time this is due to the ignition switch failing - the contacts don't handle the current needed by the transmission. The best solution is to implement a simple relay to take the load off of the ignition switch and let it carry the load. Some places make the kit for $50 or more, but a simple Bosch relay like is used on fog lights is all they are selling you with some wire and connectors.

Find a wiring diagram and track down the wire. You might use a meter to verify the voltage to this circuit just for confirmation. Good luck.

[tanker]

When mine was new I also had transmission problems??!! After 3 trys GM found a bad ignition switch, been fine ever since. smile.gif

[normanby]

Thanks for thr replies. My tranny is a 4L80E, forgot to mention that.

I took my truck to a shop today and they were able to scan it. They Tested and retested all electrical components (solenoids, switches & valves), all working normally. They then installed an oil pressure guage and tested all shift point pressures and main line pressure and found all to be within spec. They believe that that the problem seems to be caused by worn over drive clutches or broken sealing rings. Unfortunately the closest shop that can do that work is 335 miles south of me :-(