TH400

[55 Tony]

Hi Cliff, I have your book on Q-jets and the one on the th400 also, so I thought I'd try asking a th400 question.  Years ago I put a transkit shift kit in it and I have my governor set to shift at 5500 at WOT.  Worked for a long time.  Now sometimes it won't do a 1-2 shift, but it will if I let off the throttle for a half a second then back to WOT.  2-3 seems fine.  To add to this, if I disconnect the downshift solenoid, I can then shift manually just fine.

I have gone over the regulator a few times and all seems good.  I removed the valve behind the vacuum modulator, it came out a little rough so I got rid of the sharp edges and put it back in with a new modulator.  No change.  Should I just remove the valve body for cleaning and pay special attention to the 1-2 shift valve?

[Cliff Ruggles]

That would be a good place to start.

Might want to take a look at the governor as well, to make sure it's not sticking......Cliff

[55 Tony]

Thank You Cliff!
Also I'm pushing a little over 400HP according to weight, ET, and MPH.  I know that isn't much compared to some others, but when does it get important to install one of those "case savers"?  I'd really hate to loose 2nd gear engine braking since it's a street/strip car, but I'd hate it more if I ruin the case.  I am using the beveled snap ring that still fits snug enough to need to be "staked in".

I forgot to say that I did inspect the governor a couple times and it seems fine.  In fact I have a spare one calibrated differently and tried it with no change.

[Cliff Ruggles]

The TH400 doesn't have a lot of trouble with pounding out the case lugs at the center support like the TH350 does.  It's a bolt in deal and very well retained by the beveled snap ring. 

I have beat these TH400 pretty hard and logged over 1000 runs with my last one behind a 455 and it didn't grumble much or show any problems in the center support area.

It finally did start giving me enough troubles to replace it.

It started doing a "slide-bump" on the 1-2 upshift, but only under full power, fine otherwise.  I removed the VB couple of times and checked everything you could without pulling it, no change.

Removed it at one point, everything inside looked fine.  No evidence the 34 element sprag wasn't holding.  I replaced everything related to the 1-2 upshift anyhow, and no improvement.

At this point I just built another unit and it's flawless.  Parked the old one under the workbench where it's still sitting since 2009........Cliff