TH350 Squealing 1-2 Shift
I've got a TH350 behind a Rocket 350 in my '70 Cutlass. When I bought the car about 4 years ago, I was told that it had a shift kit installed. It gave pretty firm shift into second and sometimes chirp the tires a little. When I pulled it out this spring, it started acting up. When I go easy on the gas, it still gives a good shift from 1 - 2 at 35mph. (It's got a 2.72 rear end.) If I get on the gas in first, the transmission starts squealing at 35mph (sounds just like a belt slipping). It will keep squealing until I let off the gas a little and then it shifts into second gear. Everything fine in 2 - 3. Everything else about it seems fine.
I've checked the fluid level. Fluid doesn't smell burnt. No signs of fluid at the vacuum modulator. I checked it with a vacuum gage, and it is sealed. Vacuum signal coming straight off manifold with nothing else attached. No leaks in the vacuum line. I've got a pretty steady 18" Hg at idle. My guess is that the squealing is caused by partial pressure getting to the 1-2 clutch. I suspect that the vacuum modulator or modulator valve are sticking or not getting full travel. I've never worked on transmissions. These are just guesses from reading books and postings here.
Any suggestions on anything else I need to look at? I'll probably tackle this problem myself, but I wanted to see if anybody else has seen or heard this before.