Steve Cattaneo

Mspiegle,

Are you running a forced induction kit on the GTS, if so?
Were are you pulling vacuum for the modulator.

mspiegle

Yes I am. I am pulling the vacuum signal before the supercharger (so the transmission will never see boost). I tried unplugged this just to see what would happen. I think there was a very slight change (shifted a little harder), but not very noticeable.

Steve Cattaneo

The source of Vacuum to the modulator should away be manifold vacuum

TO ELIMINATE VACUUM AS THE CAUSE OF YOUR SHIFTING PROBLEM

Install a vacuum gauge on the transmission line at the modulator and quickly opening and close the throttle, vacuum must drop to below 5”. The needle on the gauge should act as an extension of your foot, foot down needle drops foot off needle comes up. The needle must RESPONE Quickly WITH NO LAG, DELAY.

mspiegle

Steve,
Due to the way the system is setup, pulling vacuum before the SC is just as good as pulling vacuum from inside the mainfold. I can easilly get the vacuum signal from inside the manifold, but will the transmission have issues if it sees pressures above atmospheric? I have put a vacuum gauge in-line with the transmission and the pressure mimics throttle movments (the instant the throttle is open, vacuum drops).

I don't know if i mentioned it before, but this car has been driven 7-8K miles with a supercharger and hasn't had any other issues. Other supercharged cars with automatic transmissions have more miles than this and still don't have issues. I believe this failure *may* be due to the ATF not being changed in a while, but I am not 100% certain. What do you think will fail first in a transmission that hasn't had the fluid changed?

Thanks for your help!

mspiegle

I might have found the culprit. This spring was in the fluid pan when I removed it. It looks like one of the hoops is broken off. I'll check the WSM tomorrow for this spring, but if anyone happens to know where it came from, let me know!

Schocki

The spring that you see holds a a pin in place (I think it,s called a lock out pin?). PET # 722 993 001 0

I don't want to disappoint you, But I'm driving without this thing since my last ATF change (12 months ago). Found it in the pan and never had problems before. Changed the fluid and didn't wait for the part to arrive, because my GTS is my daily driver. I ordered the spare part and will replace it with the next fluid change. The car runs just fine no problems

mspiegle

Dang it...

Alright, time to pull off the valve body and see what's up. Thanks for that info!

Schocki

Take a look at my post about my previous tranny issues. There is a picture with the tranny pan removed. Piston and spring are circled..

https://rennlist.com/forums/928-forum/180187-automatic-slips-from-2nd-to-3d-sometimes.html

mspiegle

The one you have circles is where I am missing a spring. According to your thread, that is the control pressure piston. Did you get yours sorted out?

Schocki

I bought my car with the spring in the pan. I saw this the first time when I changed the ATF.
I had no replacement spring and drive the car since then without it.
No issues at all.