[Socrates]

I put a TH400 in a friends car that has maybe 2k miles on from use in another car, a 70 Cutlass, where it shifted perfectly last time it was used (couple years or so). The trans looks good inside, good fluid when drained, not burt, and appears full by the dipstick. We put a new filter in it and all new fluid before the install.

Problem is that the trans does not seem to shift at WOT now. Blasting onto the highway from a stop, the engine bounces off the 6700RPM rev limiter quickly. If you let off the throttle it will eventually go into 2nd gear. Same thing going from 2-3. This all with the trans in Drive. I removed the governor and installed one factory and one heavier #3 and weight from the old B&M governor kit, which should put the shift point in the 5K range, and still the WOT shift doesn't happen, or at least it still bounces off the rev limiter.

Driving around town at low speeds it shifts into the gears ok, though if you blip the throttle a bit there appears to be a bit of slipping once the trans is warm, where the engine revs sharply though the car doesn't launch untill enough throttle is open. There are no notable sounds from the trans, though the engine/exhaust are loud in this car.

This trans shifted beautifully in the previous car it was in when driven a few years back. We're stumped. Any suggestions as to what to look for?

Could the governor somehow be sticking or defective? Could the kickdown be stuck or defective? The B&M shifter linkage seems misaligned a bit, too, if that could be a contributing problem? The tranny cooler lines are both warm after driving, so it is circulating fluid, and the vacuum modulator is hooked up to a manifold vacuum source, fwiw...

[TTS]

If I had to guess- Low line pressure. You also mentioned possible slipping when warm.

The governor isn't going to stick only @ WOT.

I would bet on a pump problem, since the trans was moved to another car.

[Socrates]

Low line pressure...Interesting. Could the wrong gear in the pump cause this? We opened up the front pump to replace the gear in TH400 as a botched converter install sheared off the tangs in the drive gear, and we possibly put the wrong sized gears back into the pump....

Should we tear into the trans pronto and measure the clearance on the front pump drive gear before moving the car another foot? Could this cause damage to the transmission? I don't recall the specs here, either, any help there??? Thanks so much!

[TTS]

All 400's use a .727" gear set. TH350's use .721", .723", .725", .727".... so they'll look the same, so always measure the thickness. Also make sure the pump is even usable, if the rear has been ground down from a mis-stabbed converter it has to be replaced (must be the same) or machined.

[stevep]

Did you test main line pressure with a gauge? It only takes a few minutes to do it.

[Socrates]

We used a .727" gear set for sure in this Th400. No major wear was seen on the pump, though I admittedly didn't look that closely either.


stevep, how would I test the main line pressure? Any common shop tools or gauges I might have to do this? What should the pressure range be? Low enough for a fuel pressure gauge to read?

[TTS]

There's only one tap on the case for pressure. A 300 psi gauge will do, check ~170psi or more @ WOT stall. Don't do that for more than a few seconds, it really heats things up.