Chevy and GMC Duramax Diesel Forum banner

HELP! 93 6.5 4L80E Trans issues

5368 Views 3 Replies 4 Participants Last post by  rip91
Hello I hope I am putting this thread in the right place, I have made a few searches and didnt come up with the info I need.

My dad has a 93 plow truck its a 2500 4x4 with 6.5 and the 4L80 trans. The rig has about 140k on the odo, and the rig had never had any previous major failures, it was owned by the gov't and they gave us the spotless maint history when we bought it. Last winter the the trans started acting up, occasionally shifting "into neutral" when it should have grabbed 4th gear. We changed the fluid and filter, which really looked decent for a gm overdrive, that had 25k since the last service. We drove it some more, and it seemed to have fixed the issue, you could tell right away that it was different.

Time went on, out plowing one night and the trans lost 3rd and 4th gears.
Took it out and sent it to a local guy who had a very good reputation with gm overdrives.

Six months later we get the unit back, and install it. It came with a wiring (adapter harness) that I wasn't really sure why, but he said it needed to be done, it was an update that these units required. I as carefully and accurately as possible depicted which colors were which, and spliced the wires acccording to the instructions. (Many of the factory ends were hardened, and stained and difficult to see the real original color, such as whites and yellows and tans, but I peeled back the looming far as possible and made sure to get the colors right.

The trans works great for about a month, and then not even working the truck, just driving on the highway, it doesnt shift to 4th gear. Check fluids, and all is good, no color, no odor, just normal all around. Called the tranny shop, no answer, phone is disconnected. Called his wife at work, she says he will call us back soon as he gets home from looking for a job..... he never calls back.

I have a ton of experience with fixing transmissions, manual and automatic, but I dont care much for the late model stuff, didnt have time to learn the little tips and tricks of the 4L80, and so I turned to this guy. Can anyone give me some tips and such related to this beast so I can fix it. I suspect its some little solenoid or something that was the issue in the first place, prior to the $4000.00 rebuild that fixed nothing.

Thanks for your help!

See less See more
1 - 4 of 4 Posts
:eek: Your still alive?! :rof

I remember you posting alot when I first joined here.

Anyways... That sucks.. Id try a local tranny shop and tell them the story. If its a small place maybe they can give you advice.

Trans are a little tricky. My dad owns a repair shop and rebuilding trans is the only thing we dont do :cool:

An experience I had in my old 93/6.5/4L80 was dollying/towing a car in a 300 km round trip (stop light starts in OD), next highway trip around traveling unloaded, no OD... Got lucky with disconnecting the batteries to let the computers reset, got OD back! Personal lesson, not to use OD unless on high way... Even seen a sticker in the door jamb of my neighbors 97 explaining the not to use OD unless at highway speeds!
Not sure if you have your issue fixed but my 95 6.5 has acted up like that on me a couple of times. I have never been towing at the time but I could tell it would not shift. If you have any reselution on this matter I would like to hear it. Mine eventually shifted to OD after it cooled down for the night.
1 - 4 of 4 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.