Auto trans O/D problem

[Cuppster]

I'm driving 1995 SE, OBD-I, auto, no HICAS, no LSD.

For a while now I've been having a problem where my car shifts up into 4th gear (O/D) normally, but as soon as I back off the accelerator it drops down into 3rd. If I open the throttle again, it shifts up normally, then shifts down when I close it again. The simple solution is just to drive with O/D off, but that gives crappy gas mileage, and the motor makes a terrible racket when its spinning at 4000 RPM to go 65 MPH in 3rd gear.

It was driving me nuts, and all the transmission places I went to couldn't figure it out without a complete teardown ($400 just to figure out what's wrong - no thanks). I checked all the sensors myself (TPS, revolution, etc) and found nothing wrong. I had resigned myself to just replacing the whole transmission. (And no, I'm not interested in doing a manual swap right now).

Eventually, I pinned down the symptoms to: it only stays in 4th while the transmission is under some load, such as accelerating or going up hill. After reading some of the other transmission posts here and elsewhere (for the third or fourth time), I got the idea this week to start driving with some of the electronics disconnected, just to see what would happen.

Viola! When I disconnected the line pressure sensor (or whatever it's called, the slim connector near the power steering reservoir) the problem went away. I'll be damned! I decided it must be a solenoid, specifically, the line pressure solenoid. So 4th gear is only available when there's a higher-than-normal amount of pressure in the valve body (such as when it's under load, or the sensor is disconnected). I've already replaced the TCC solenoid, so why not the others?

But now I'm not so sure. It might be the valve body itself. Maybe a valve is wearing out and letting too much fluid pass (or not enough, or something). I have noticed that it still has trouble between 3rd and 4th with the throttle completely closed and the RPM's are below 1000, even with the sensor disconnected. And sometimes it happens above 1000 if I've been driving for a while.

I know this is a lot to read, but I'm hoping someone here can give me an informed opinion. Should I replace the solenoids or the valve body? At least I know its not mechanical now.
Modified by Cuppster at 7:36 AM 10/16/2007

[Cuppster]

Bump for assistance.

I'm kind of leaning toward just replacing both.

[ThuG LyFe]

i just did a 5 sp swp if u were in NYC i could've just donated it for u since the shop took the transmission anyway...

hope u figure it out!

[Cuppster]

So I replaced the upper solenoid pack, and the problem is fixed. It was probably a 10-year-old line pressure solenoid. Incidentally, don't remove your valve body while the transmission is on the car, unless you have four hands or a transmission jack to hold it up while you put it back on. It's a PITA.