rebuilt auto transmission problems

[daughters-car]

I got a 1997 GST spyder with a bad automatic transmission for my daughter last month. I rebuilt the trany myself, not my first trany rebuild but it is my first computer controlled trany rebuild. It was in such bad shape that I had to replace the entire front pump and torque converter along with all new frictions/steels and all seals. I reused all the electronic solonoids. I didn't mess with the kickdown servo since I don't have the special tools for that. I've put about 200 miles on it since the rebuild and something's just not right - I'm not going to trust this car with my teenage daughter like it is currently acting. At first I though maybe the transmission computer needed to relearn or something and it would just com out of it, but it's not getting any better.

Sometimes it works perfectly fine, but sometimes when shifted in gear it doesn't fully engage. It may engage reverse good, but then not engage good in drive. It may not engage reverse, but then engage good in drive. Or it may not engage either reverse or drive. It always eventually engages by shifting in and out of gear several times. Or (and I don't like doing this) revving the engine and it will then engage harshly - like slam into gear and chirp the tires. Once it goes into gear it seams to shift OK most of the time. Sometimes it seems to slip a little between first and second gear, or do these just have a really lazy 1-2 shift? It has a very crisp 2-3 shift. The only other symptom I am getting is that sometimes at around 40-50 mph it will just suddenly downshift - giving it a little gas and then backing off will force it to upshift again. The shift linkage is working good and I have re-adjusted it several times just to make sure it's not an adjustment issue. The tcm shows no codes. The fluid level is correct, although I noticed you cannot get a propper fluid reading in park - it must be in nuetral.

It's obviously not a mechanical issue since it can work correctly sometimes. Is this likely one of the solonoids sticking or something? Need some advice on how to diagnose this issue please. Thanks,

 

[tballer25]

I am assuming that by the TCM you are talking about the TCU (transmission control unit). I am going through a problem with this as well but my symptoms are different. I would say it is the TCU, as that is what sends the signal to the transmission to shift and engage properly. My problem is that I can't figure out how to get the damn thing out. Its nested close to the firewall by the gas pedal in my 98. (Im pretty sure yours is in the same location for the 97). Maybe this isn't your problem, but hopefully it gears you in the right direction. I hope this helps.

 

[97gst_spyder]

Its time for you to check for tcu codes via the obd2 port. You can use a special (expensive) code scanner, or an analog multimeter.

There is a thread about it on here, also on atdsm.com.

While your looking at the car, check the tps on the throttle body. If that sensor ####s up, all hell will break loose. Trust me on that one.


If you want another tcu for it pm me. I have a few extra.

 

[daughters-car]

OK, I checked the TPS and it checks out good. Still no codes in the TCU (TCM). I purchased a transmission pressure tester and started following the dignostic charts in my manual.

Anybody any good at following these stupid diagnostic charts? I managed to pressure test all but the number 6 hydraulic pressure (end clutch pressure) last night following the procedures in the manual. I couldn't test the no. 6 pressure because it will require a custom made 90 degree fitting to get the pressure tester on that one (working on it).

I did find some abnormalities, but the diagnostic charts don't make sense! My no. 2 pressure (kickdown brake apply) in the no. 2 condition is high (should be 14-30psi or 36-43psi but I get ~120psi). My no. 7 pressure (low-reverse brake) is low in the no. 6 condition (should be 43-64psi and I get ~30psi). If I follow the dignostic chart for the no. 2 pressure abnormality it refers me back to case 1 (because the no. 7 is also abnormal) which is all pressures being abnormal, but that's not my situation. Everything is normal except those 2 situations I listed above. If I follow the dignostic chart for the no. 7 pressure abnormality it also refers me back to case 1 (because the no. 2 is also abnormal). This is getting me no where!

If I ignore the references back to case 1, then the no. 2 pressure problem tells me to replace the TCM because it is only abnormal in the no. 2 condition and because the no. 5 pressure is normal in the no. 6 condition.

If I ignore the references back to case 1, the no. 7 pressure problem tells me to go to case 3 (which sends me down a different branch of the no. 2 pressure chart). But I get stuck at the box that says "no. 7 pressure in no. 6 and 7 conditions and no. 3 and no. 4 hyd pressure in no. 4 condition are normal?" - part of this is true and part of this is false for me so I can't determine which branch to follow. No tells me to overhaul the valve body and yes tells me to overhaul the valve body or replace the kickdown servo seals.

I'm lost and seriously considering giving up on this car and getting something else for my daughter to drive! Please help if you can.

 

[rEclipserGST]

Auto's are easy. I've experienced slightly similar issues before. Check the following:

TCU - swap in a good one or pull codes, check for damage
ECU - ^ and make sure it is not stuck in LIMP mode
TPS
End clutchs - IPT sells replacements, easy to change especially if you rebuilt a tranny

Fluid level - check when car is running, shift thru all gears, recheck fluid

 

[daughters-car]

Thanks for the input. I did pull the TCU (TCM), open it up and look for any damage. It looked good and smelled normal. I imagine I would need the numbers off of mine to match up with a replacement if I'm going to try to swap in a different one - right? The TPS checks out good. The end clutches (and everything else in the trany) are new, no need to replace. The fluid level is good.

I made an adaptor and got the number 6 (end clutch) pressure tested last night. It tested good, so my only issues are what I said above. Basicly the kickdown brake apply pressure with the shifter in the D position, trans in second gear @ 1,000 rpm should be somewhere between 14-43 psi, but I am getting about 120psi. And the low reverse brake with the shifter in the L position, trans in first gear @1,000rpm should be 43-64psi and I am getting about 30psi. Everything alse checks out within spec although I did notice the no. 5 (rear clutch pressure) in the no. 6 condition (Low, 1st gear @1,000rpm) the needle on the test guage bounced up and down. The needle was nice and steady during all other tests. Not sure if the bouncing needle means anything since it's not a condition listed in the manual. So, I'm still stuck on where to go next since the diagnostic charts don't make sense.

 

[daughters-car]

The common possible issue in all the diagnostic charts for the problems I'm having was abnormal reducing pressure. My range is 50-70 psi and my initial testing showed 50psi accross all test cases. I decided to drop the pan and try adjusting the reducing pressure toward the high end of the spec, especially after reading an article from Kiggley that said the only purpose of the reducing pressure was to soften shifts.

Well, I got it adjusted to 70 psi, but even after driving it around for about 100 miles now since the adjustment it made no change to any of the issues I'm having. I give up - I'm just going to leave it the way it is and let her drive it until it either goes out again or straightens itself out!