Th400 won't shift...
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Th400 won't shift...
I have a th400 with a Hughes performance manual/automatic valve body and I just installed my hydraulic roller cam it was a comp 12-444-8.. From what I see it has about 7" vacuum.. I think everything is set correctly and that is about the highest I can get.. When I drive it down the road in first and manually put it in 2nd it won't shift. It will hold and I can rev to 7000. When I put in drive it will shift.. Hughes told me one day it was the modulator but you'd think it would do that in drive... Any ideas or suggestions?
Team Owner
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I have a th400 with a Hughes performance manual/automatic valve body and I just installed my hydraulic roller cam it was a comp 12-444-8.. From what I see it has about 7" vacuum.. I think everything is set correctly and that is about the highest I can get.. When I drive it down the road in first and manually put it in 2nd it won't shift. It will hold and I can rev to 7000. When I put in drive it will shift.. Hughes told me one day it was the modulator but you'd think it would do that in drive... Any ideas or suggestions?
There's many ways to do a TH400 for shift control and I'd think Hughes likely does them all. I haven't had a TH400 in along while except the one in my 4.3 truck. I've had a few and also a clutch-turbo a very long time ago.
I believe the governor was somewhat unusual in a TH400, you could leave in 1st and you could force a 2nd gear by just a "blip" of the throttle.
Vacuum is certainly less than desired. Whose modulator?
Last edited by WVZR-1; Aug 31, 2015 at 08:28 AM.
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Th400 won't shift...
It's a pioneer brand modulator. I took out the screw also.. Makes no difference. Had it on stands running through the gears and I think it might only be shifting once.. Maybe it's skipping 2nd all together.. I rebuilt it myself and I'm no transmission expert. I've been told the sprag may have flipped. Idk
Le Mans Master
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From: near the thumb in the mitten
Are you sure it's actually starting in 1st gear. 400s can take off in second. What is rpm vs mph. When you feel shift going into "D"; do you feel downshift when shifter is moved back to "S" or "L"? What year is trans. early 400s had 16 element sprag for second gear B&M sell a a stronger 32 element one. Either can be installed up side down or backwards but it would be 1st gear only. Later 400s used a roller clutch it's not possible to install it wrong. It is possible to clutch lips seals in wrong or cut them during installation. Leakage should show during a pressure test. Non-modified 400 will shift 1-2 at max governor speed even in manual low. There is a hole in valve body that causes this, blocking it disables "shift override".(commonly part of shift-kit). You may want to have a local transmission guy help you diagnose problem. Good Luck
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I got it fixed and I know for a fact that it was skipping 2nd gear cause you can feel 1st and 3rd.. It is a manual auto valve body so it won't auto shift in 1st or 2nd. It was a broken front servo piston. Got a new one put it back together works perfectly.
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I don't have any pictures of it but I used 1/4 steel plate and bolted it to the beam and where the transmission mount was and at the top and bolted to the tail housing bolts. Hard to explain hope that makes sense.
