Technical 400 turbo shifts into 2nd gear in 12 feet

I'm not a transmission expert at all, but have a simple question. I had a 400 turbo rebuilt by a transmission shop far from me. (long story) I have it in an 1900 lb T-bucket. If I take off at any speed it shifts into 2nd gear before I can blink. If I manually shift it, it's really lazy to achieve 2nd. Third is just fine. Before it was rebuilt it would light the tires up in 2nd and I could leave it in drive. Someone told me to check if the vacuum modulator had a screw in the hose nipple, and to turn it in a couple of turns. I know if the modulator hose is pulled off it will not shift at all. This is just a pain in the ass and I don't know what I'm doin'. Any ideas out there? Thanx

 

I would have you check the governor, but you say 2-3 is ok. So with this in mind, has this transmission had a shift kit put in it? If so, then I would think the 1-2 shift valve or related parts in valve body might be the problem. That would be where I would start, in the valve body.

 

Invest in an adjustable governor weight kit & get a couple extra gov gaskets. Last summer I experimented with the exact problem & I couldn't be happier with it now. I've sold adjustable modulators for decades at work & put a few in & in the th400s the adj govenor kit seems to yield great results. Super easy to do & you'll barely loose fluid. Flux

 

If you turned that screw one way go back the other way. The module should be reset and then find (search the net is faster) which way the screw goes to slow down or speed up the shift point.

 

Turn the screw in ..I mean way in ..clockwise, and see what it does.
I doubt this is it though.
Certain shift kits and mods will mess up the governor calibration.
Without getting into detail, best way to fix this is to dick around with the governor, as stated.
Can you put it in manual low and hold it there til about 4 grand, and then shift to 2nd?
What does it feel like?

 

The TH400 is designed to have an forced 1-2 up shift when in manual low.
This can be eliminated by grinding two flats on the 1-2 shift valve and blocking an exhaust port in the valve body.
These modifications are also part of most shift kits.
The exhaust port is usually blocked by driving a check ball in it, maybe this check ball fell out during the rebuild or the rebuilder replaced the 1-2 shift valve with an unmodified one and left the exhaust port blocked.

 

In a light car with a low gear the transmission will shift up from 1st to 2nd rapidly unless you are shifting it manually. that shift points can be altered by altering or changing the springs in the governor. That is the easiest way.

I have discovered that some T 400s have a more sluggish 1-2 shift then others. I have one that I robbed out of an old gasser with an autostick valve body that is a little sluggish from first to second and what I do to over come it is lift ever so slightly. it works for me and has yet to cost me a race. But I am sure that there is a better solution for that and maybe when it is time to freshen it I will address the issue.