My 95 seville with 4t80e transmission won't shift in overdrive, was running great and just stopped shifting to OD. I replace both shift solenoids, no shavings in pan, fluid is great, still won't shift. HELP!

 

i would say take your ecm and get it reflashed to stock sofware...your tranny is told to shift by ur ecm...solenoids wouldnt be the problem because ur car is only haveing overdrive problems. so yea im thinking its an ecm issue.

 

Does it stay in 3rd gear, or does it "neutralize", and the engine just spins up? If it is neutralizing, the most likely problem is the overdrive band is burnt. Common on these.
IF it is staying in 3rd, and just not upshifting, it could be a valve body issue, a problem with the MLPS(manual lever position sensor, [or neutral safety switch]).
You need to determine if there are any codes stored in the system that would point you in the right direction to diagnose the problem.


My '94 had a similar issue...when it shifted into O/D, it just neutralized. Had gear ratio codes set, also. I pulled the trans, and found absolutely NOTHING wrong with it, visually. It looked perfect, other than normal wear/tear. It bothered me that I couldn't find the problem, but I had another trans already built, so I just swapped them out. I finally just decided that the original trans probably had a stuck valve, and I just wasn't in the mood to tear into it to find out.