I'm trying to figure out why my 350's trans shifts so firmly at part and light throttle. I've adjusted the modulator and vacuum control valve per the FSM. I've checked the vacuum amplifier. I get about 14" of mercury at idle, which makes about 20 psi of modulator pressure.

I've taken apart the VCV and cleaned it, replaced all the vacuum lines, verified no leaks in the climate control system... to me it seems like I need more vacuum at idle. If I hook up my hand pump to the VCV and pump it down to 18-20" the modulator pressure goes to nearly 0 and the light throttle shifts are perfect.

I'm wondering what the "correct" modulator pressure at idle (with the vacuum line connected) is. If anyone has checked on their trans could you post in this thread?

Here's a quick video I made: https://www.youtube.com/watch?v=gxVsT65PjjM You can see how the modulator pressure drops when a gear is selected, and at the end I use the hand pump to show the relation between vacuum and modulator pressure.

I'm thinking I might add a switch to the throttle linkage which operates a solenoid switching in more vacuum at light throttle.

-J

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1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket

Tesla Model 3. 205,000 miles. Been to 48 states!
Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels.
2014 Cadillac ELR
2013 Fiat 500E.