[kmeyer54]

Vehicle: 1970 Pontiac Catalina 2DHT, 400 4bbl w/ TH400. Everything is stock or equivalent as far as I know.

Background: Owned the car since 2017, replaced trans filter shortly after I bought it. Car was driven semi-regularly until early 2021 when the odd behavior started. It had to be towed home due to refusing to accelerate above around 30MPH. Problem seemed to resolve itself temporarily. I went to start the car in late 2021 and was met with a horrendous noise. Left it alone and had it trailered when we moved last year. Finally got to work on it again and found the starter gear completely shredded but the flywheel seems intact. With a new starter and some run time, the motor is running pretty good. The car developed an odd and inconsistent screech from the transmission under load, then the current issue developed within a short amount of drive time.

Current Issue: The transmission has very strong reverse, but has almost no forward gear at all. It acts almost as if the transmission is freewheeling and the engine revs without accelerating. The issue has intermittent severity, and it seems to work better when I shift it manually, but never gets into third gear. The issue is at its worst in the Drive position. It seems to get worse as the vehicle warms up, but this seems inconsistent too.

Troubleshooting:
I've replaced the filter again, which revealed extremely black fluid and some sludge (probably more sludge than is expected for the mileage on it since the fluid and filter were changed in 2017). The previous filter is the fiber element variety that is notorious for clogging. The filter element seems to have clogged and sucked itself up into the metal housing toward the tube such that you can't see the element through the cutout where it is usually visible. The car did have an overheating issue in the past like a lot of 400's, but has since been upgraded to a new radiator and a HD fan clutch which seems to have resolved that issue if the temp dummy light is to be believed. My initial suspicion was that it had fallen prey to the notorious filter clogging issues which had caused the trans overheating. After new fluid and filter, the issue was more or less the same but the screeching noise is gone. The vacuum connection to the trans itself seems fine but the connection at the carb was deteriorating, so that has been replaced which also did not resolve the issue but may have improved it slightly. Tonight I pulled the governor and found the pin stuck solid. I was able to free it up and get it to move freely, but I'm not sure if it is free enough to work properly. I re-installed it and test drove the car. It started out weak but moving, though not above 35 MPH or so. It started to act like it was going to free up and got up to 45 or 50 MPH, then completely lost all forward gear and forced me to reverse back to my driveway.

I have yet to test the vacuum modulator and I don't have a vacuum gauge on hand. My thought is that that is the next logical step, but from what I've been able to find this issue doesn't quite seem to fit the symptoms of a bad modulator or low vacuum since it is losing forward gear completely at times. I'm also considering replacing the governor just to be safe. Other than that I would think it would have to be something internal that would require teardown and rebuild.

Anyone have any experience with similar issues or any further troubleshooting tips? Hoping to avoid a rebuild for the time being if possible. Unfortunately my 1995 Dodge Ram 1500 developed a very similar (almost identical, actually) transmission issue as I was on my way back from ordering th filter for the Catalina at O'Reilly's. I could really use a working vehicle at the moment besides the wife's Toyota Sienna.