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I have a 1970 Cutlass Supreme that I have put a 455 and a TH400 transmission out of a 1974 Olds 98 into. My problem is when it is sitting parked in my garage and it gets hot in the transmission leaks fluid everywhere. I believe it is leaking through the yoke. I have installed a new tail shaft seal and a new oring on the out put shaft. I am at a loss as to why it is still leaking like this. It is not the original drive shaft. The drive shaft was shortened when we went with the long tail shaft transmission. Any ideas?
Your statement doesn't provide confidence in having identified the "source" of the leak. Don't guess, save time & headaches. Clean up the casing as best you can. Add some UV dye to the fluid. In short order (after a short drive) you'll find the source of the leak. Dye ~$8-10, small UV pen light ~$10 (or use the UV light from the teenage kid next door). Stevie Wonder could find that leaking trail. This is the reason a mechanic uses these dyes. Dye & UV pen light are readily available at most reputable auto parts supplies stores.
I remember someone joking that the TH400 can leak anywhere between the bellhousing and the tailshaft. I have same issue on my 70 Cutlass SX even after having someone rebuild the TH400 for me. Shift shaft seal is a common one. front seal, rear seal, pan gasket, dipstick tube o-ring, etc. If shift shaft has a groove worn in it, the seal won't stop leaks and need to replace shift shaft. Some people pound in 2 shift shaft seals and that sometimes works. Rear yoke seal could be an issue and I think there is also a bronze bushing in there that could be bad and causing leaks. Or rear yoke has a groove worn in it, so the new seal doesn't seal properly. If pan is warped, that can cause leak - Felpro makes a thicker pan gasket that sometimes helps. Lots of places to check - I would put a big piece of cardboard underneath and see if you can pinpoint it.
I have a 1970 Cutlass Supreme that I have put a 455 and a TH400 transmission out of a 1974 Olds 98 into. My problem is when it is sitting parked in my garage and it gets hot in the transmission leaks fluid everywhere. I believe it is leaking through the yoke. I have installed a new tail shaft seal and a new oring on the out put shaft. I am at a loss as to why it is still leaking like this. It is not the original drive shaft. The drive shaft was shortened when we went with the long tail shaft transmission. Any ideas?
Check the TH400 vent (make sure it’s clear), verify fluid level hot, and inspect the slip-yoke for a tiny end hole plug it if present. Worn yoke surface or loose output bushing can also cause that leak.
