transmission slipping/not shifting

If a fluid flush & filter won't fix it, you need a rebuild, a replacement, or a 5-speed swap…

A fluid flush & filter won't fix it, your friction disc's are fried. Don't waste money on trying to bring it back, it won't. As said already, "you need a rebuild, a replacement, or a 5-speed swap".

put a good amount of miles on it after this post. i forgot to mention the car had been sitting untouched for over a year in a barn. i started and shut off the car a lot during the time to test the amount of time it took to get into shifting. my original thought was the modulator, but i think otherwise now because once it begins to shift, it does so until the car is off. im going to be doing a filter/fluid change asap and im thinking that will solve my problem. i think the filter was gunked up from sitting and just needed to be worked a bit and freed up. the last time i took it out after sitting for about 20 minutes, it took about a minute to start shifting compared to 5 minutes when i first started driving it. i think it is just the fluid and filter

If you have no idea how old the auto-tranny fluid is or how long it sat unused. Do a flush and fill with the right fluid. If that fixes your shifting problem, great. If not, your only out a small amount of time and money on fluids. Also get that timing belt, tensioner and water pump done as soon as possible if your not sure of the age or condition. These are interference engines, lose the timing belt, even slip a tooth or two, and you can kiss the valves and pistons goodbye as they destroy each other.......Not trying to alarm you but it is probably the #1 engine killer for these cars. Better safe than sorry. And again its not really difficult to do, unlike some of the guys here I am not a professional mechanic just a guy that likes to mess with cars. I did my own with am FSM, info from this site, and Xenon's website http://www.xenonz31.com/timingbelt.html in the driveway in a single afternoon.

the timing belt is next on my list after the transmission is fixed. picking up a filter and fluid tomorrow. the fluid level is quite high for some reason, and i havent seen a shift into 3th yet, but the shifting has been more consistent lately. once the engine is warmed up, all it takes is one good hard push to ~6k rpms, and it usually starts shifting somewhat normal. it seems a tad late from the other transmissions ive seen, but thats probably due to the fluid level and filter

Trust me, its not gonna get better on its own. The fluid level is high because someone tried to "make it work" by adding fluid. You can waste a few bucks on fluid and filter just in case you get a miracle though. I've owned three auto turbo car and I have a little experience with them going bad and having them rebuilt. They are expensive to rebuild, $1500-$1700 and you can buy all the parts for a 5 speed swap for around $500. If you are determined to stay with an auto trans, (I have one auto turbo car I don't plan to change) either find a low mile unit and do a partial repair with a shift mod or totally rebuild yours. If you ever overheat your car to the steaming, spitting point, immediately change the filter and fluid or its toast. 84-85 auto will not work in 86-89 due to the electronic shift system. It can be made to work so some say but I don't know that and my trans re-builder said he would not warranty such a swap.

Automatic transmission just pulled from my 87 Z31 Turbo car.
Could be yours, can you pickup in northwest PA or arrange for shipping.
It is on a wood pallet, ready to go
Pdfflyer@Roadrunner.com

PM me if you need parts for the timing belt change.

Did the filter and fluid today. Put in 7 quarts And it still read over full and the problem continued, if not worse. Before once it shifted it stayed in the gear now it will shift, but slip out and go back to 1st. Did get overdrive to work for a little bit though. My guess is a valve or something is stuck or clogged inside the transmission. Going to be replacing the modulator and vacuum lines tomorrow and see if that works. Otherwise, I may be doing a 5 speed swap sooner than expected. Also found some slop in the transmission. Got the back wheels off the ground and turned them back and forth, and the whole driveshaft was solidly tight and the splines coming out of the transmission turned a minor bit. Not sure if its due to the fluid issue, or something wrong internally.

Your valvebody probably collected a bunch of dirt with the new fluid… I did this on a caravan I had, everything got worse for the first week, then it started clearing out, after 2 months it behaved better than a "rebuilt" trans of the same generation in my mother's caravan

I ended up donating my trans to someone else's caravan when I finally gave up on the vehicle (someone rammed a door, fuel pump died etc..) and it went another 80k kms (290k kms when I gave it to him)

So basically I should see if it will clear itself out before buying a modulator?

Correct the fluid level asap. Over filled autos will aerate the fluid and damage components from excessive slip and will also burn up the fluid in no time. Air compresses, causing slip, fluid does not compress. Fix the level first and see what happens.

Trans need to be warm, in P or N with engine running to get proper fluid level readings.

I think I found the issue. Transmission worked flawlessly earlier today after checking the vacuum line to the modulator, but after driving a bit and letting it sit, I think the vacuum line vibrated itself a little loose, and isn't getting the proper seal to allow the transmission to work properly. Going to find a new segment of hose to try and get a better seal on the modulator and see how that works .

so the problem continues. when the car is cold and just starting up, it shifts and everything works flawlessly. but after it warms up, if i shut the car down and start it up again, it goes back to the original problem of staying in 1st gear and when it does shift up, it slips out easily. not sure why. its beyond my knowledge..