TH400 won't up shift...

I finally got to take my 54 Buick out for the whole day after a long power train swap. 401 nailhead, TH400 with a shift kit both fresh and completely rebuilt. Was breaking in good and running fine most of the day. Finally starting to get it some miles and a little speed after the last weak spend doing intial break in and bug chasing. I got on it a little bit leaving my last destination and the trans completely stop up-shifting. It stills goes into reverse and neutral and even first, and second, but in drive it seems stuck in second. Im not familar with automatic trans as much as I should be so I need a help to fix the problem. Thanks

 

check the atf to see if its still red not brown and stinky

 

check your basics: tv connection and that the shift linkage is allowing the shaft to settle solidly in the detents.

Also inspect the vacuum modulator/vacuum line for any issues.... after that, you'll need to look into things like sticking valve body or pressure issues

 

Might sound simple, but with those symptoms it sounds like the modulator failed, or the vacuum line came off!

 

Or if you used a rubber vacuum line, it finally burned through.

 

Thanks guys... now I have a direction and hopefully it is that simple

 

Check the governor assembly especially pay attention to the gears to make sure that they are meshing up correctly and the governor itself is free and not binding...hope you the best of luck

 

X2 on the governor. Pull it out and check that the plunger moves freely.

Even the smallest nugget of debris can lock it right up.

 

That's what happened to mine... the modulator failed and started sucking the ATF right out at a Quart every 5 miles

 

if this 400 shifts the 1-2 shift but not the 2-3 I don't think it's the governor. As for the TV comment, a 400 doesn't use a throttle valve connection. A 400 will over ride the manual valve and shift even if the shifter is left in low. check vacuum at the modulator

 

I found a governor in a 700R4 that had a bur in the bore (of the governor, not the trans) that restricted the overall movement of the plunger.

It shifted 1-2, but nothing else.

Still, check the vacuum.

 

I thought I would update so If anyone is searching.

So my transmission guy fixed the problem. The governer gear wipped out because of a small amount of debris. He fixed it for free since they built it and it only had like 100 miles on it. He said if I ever have any trouble to bring it back in and he will take care of it. Dan is the man at High-Tech Transmissions in Sheridan, Wyo.

Whoo Hoo back on the road and it was an easy fix.

 

WOOT!

WOOT X2!, for your transmission guy for standing behind his work.