I swapped a 4T60 from a 92 Cutlas supreme with 68,000 miles into my 88 GT. I used a governor and cap from a 80's Cutlas Ciera because the 92 Cutlass Supreme governor and cap is not compatible with the Fiero speed sender. After the swap all was well but shifts were very firm and noticable downshifting was anoying. Also shifting from park to drive was a little harsh but I drove it for months like this because it wasn't too bad. I decided to reinstall the governor that originally came with the transamission (after I pressed off the incompatible reluctor wheel) in an attempt to fix the harsh shifts. After doing this now the trans goes into neutral at stop signs and I have to rev up the engine to get it to shift into first or I can put the shifter into neautral then back to drive. Okay the sensible thing to do is put it back the way it was. Same problem now no matter which governor I use. Any ideas????? Please help!!!!

Did you make sure the transmission fluid was at the proper level?

Yes trans fluid is proper level. I have adjusted the adjustable vaccumm modulator through it's full range, tried different settings with the TV cable to no avail. It's just crazy. What could I have done while swapping out the governor to cause this??

Swapping the governer did not cause this. Governer feed is orficed in the accumulator cover ahead of the feed pipe. This prevents loss of drive oil pressure when the governer is exhausting the most(0 PSI-0 MPH). Lets fix the high line pressure problem first. Tee in a vacuum guage to the modulator line and put a 0-300 PSI guage on the line pressure tap. Pressure at idle should be 55-75 PSI and vacuum should be at least 13" hg in drive. At 1000 RPM with hose off mod, max line should be 155-185 PSI in drive. Make sure the modulator is not bent where it enters the trans case(common on boneyard units). The mod valve in the case could be stuck also. Correcting the high pressure will fix the rough shifts, but likely won't fix the nuetral condition. That will likely boil down to a leak in the input clutch.
Marc

I finished this same swap this past summer and had a similar problem. Shifted fine, but when I came to a complete stop the transmission seemed like it was in neutral. It only took a slight bump of the shifter to get it re-engaged. I kept driving it like this and after about 500 miles, it works fine. I think some passage may have gotten clogged while it was in the junk yard - not sure how long. I agree that the hard shifting is likely related to the modulator valve. Try one of the non-adjustable ones. I am using the BTW from advance auto.

quote Originally posted by OldsFiero: Swapping the governer did not cause this. Governer feed is orficed in the accumulator cover ahead of the feed pipe. This prevents loss of drive oil pressure when the governer is exhausting the most(0 PSI-0 MPH). Lets fix the high line pressure problem first. Tee in a vacuum guage to the modulator line and put a 0-300 PSI guage on the line pressure tap. Pressure at idle should be 55-75 PSI and vacuum should be at least 13" hg in drive. At 1000 RPM with hose off mod, max line should be 155-185 PSI in drive. Make sure the modulator is not bent where it enters the trans case(common on boneyard units). The mod valve in the case could be stuck also. Correcting the high pressure will fix the rough shifts, but likely won't fix the nuetral condition. That will likely boil down to a leak in the input clutch. Marc

The firm shifting is no longer a issue. With the 92 cutlass governor back in the trans I was able to adjust the modulator until I am happy with the way it shifts. The neutral condition when the car comes to a stop is the only issue. It does not always do this but mostly does. Another issue that may or may not be related is that I can feel it downshifting as I am slowing down. It kinda feels like downshifting with a manual transmission. I'm not sure if this is normal but I don't notice this in my other vehicles.
I am able to check the vaccuum with the trans in park and I have 18 HG at 1000 RPM. I need to get a T for the vac line in order to test in drive. Note to self: NEVER shift to drive with the vac line disconnected from the modulator!

[This message has been edited by carguy8t8 (edited 11-15-2013).]

It sounds like pressure rise is working for the most part. Without a guage on it, we won't know for sure. You really shouldn't feel the down shifts. The fact that you said it feels like a manual makes me wonder if the torque converter clutch is applied all the time from 2nd gear up. GM used 2nd gear oil for TCC signal on these units to prevent killing the engine at a stop should the lock up solenoid stick(the problem that plagued the 125C). 4T60's almost never have sticking solenoid problems. This problem usually is the solenoid feed orfice tube coming loose from the separator plate allowing more oil to the solenoid than it can exhuast. If this is the case, the car will feel more jerky when you accel/deccel quickly(much like a manual feels). Hope my poor description helps in diagnosis. Sorry I didn't respond sooner, but I was off for a week to hunt.
Marc