TH400 2nd to 3rd shifting losing vacuum

[xthexmadxhatter]

Drives fine until warms up then drops from 3rd into 2nd and will not shift back until completely off of throttle but apply any throttle at all and drops back into 2nd. Pulling 14" of vacuum at idle but almost zero at cruise. Has dedicated vacuum port coming out of intake not carb.

[NEUMANNZZ]

msybe the vacuum modulator is bad.

[xthexmadxhatter]

The transmission was just rebuilt and they changed it I also changed it again just to be sure

[NEUMANNZZ]

kickdown switch working correctly?

does it seem to shift at correct rpms?

[xthexmadxhatter]

It shifts at correct rpm but the detent or wot switch isn't hooked up there isn't even one on the vehicle

[transbuilderguy]

O vacummm would mean high TV pressure which would want to keep the trans downshifted basically 0 vacumm is WOT need to figure out whats up with vacumm. you vacumm at idle is low also. are you sure you are using manifold vacumm and not ported.

[xthexmadxhatter]

It's not ported and straight out of the manifold, I think i might have a ring problem under a load

[Fast305]

It shifts at correct rpm but the detent or wot switch isn't hooked up there isn't even one on the vehicle

What application are we talking about?? The only ones that I know of that did not have a WOT switch on either the car or accelerator pedal bracket were the TBI trucks and I know those wouldn't be happy idling at 14 in/hg of vacuum. Vacuum modulator controls part-throttle shifts, detent controls kickdown, governor controls all upshifts. Even if you disconnect the modulator it will still upshift at part-throttle, it would just very late and very hard.