TH400 shift problems

[Banjobend]

Hey all, first time poster here. I have a 78 c20 with a 350 and a th400 trans. I'm having shifting trouble with the 400. The shifts are very firm and the previous owner said it has a shift kit. If I get on it, it chirps the tires both shifts. It's too violent. I've adjusted the vacuum modulator as far both ways as I can, very little difference.

The other issue I have is when it shifts. The 1-2 shift happens way to soon, sometimes it even starts in second from a stop, then hunts back and forth between 1 and 2. Then the 2-3 shift seems a little late, but not bad. The vehicle doesn't have a tac so I don't know rpm numbers.

I was thinking I'd buy a stock valve body and governor to see if that fixes the issues, but don't want to throw money at the problem. Changed fluid and filter about 1,000 miles ago, fluid looked ok, and didn't see anything out of the ordinary with the governor. Any tips on diagnosing this thing?

[JohnnyPopper]

I think you nailed it when you said there is a shift kit in it.

Last time I put one in, it had mild to harsh. I chose mild and it was still hard.

I recall installing some check valves (looked like ball bearings) and drilled out select ports in the metal plate between the valve bodies.

It's been 40 years so can't say for sure.

I don't think it requires a new valve body. I would look at a shift kit for that yr/model to see what physical changes are made and reverse engineer it.

[VileZambonie]

Pull the connector off of the detent solenoid and see what happens.

[Banjobend]

Pull the connector off of the detent solenoid and see what happens.

Is that the "kickdown" solenoid? If so, I tried that and it shifts the same, except no kickdown on WOT.