Quote:
Originally Posted by tyl604
Clemson - I think we are in agreement too. Here is my hands-on experience: On my 81SD I had an indy replace the transmission. I tested it by unhooking the plastic line from the VAV to the tranny and I plugged that line into the Mityvac so I could pump some vac to the tranny. Upon driving around I found that the upshifts were good and smooth - no vac. However the downshifts were quite clunky.
So I drove around more and tested the downshifts by pumping up some vac before coming to a stop. Applying vac got rid of the clunk and I got a smooth downshift.
I was never exactly able to figure out the vac modulator or its purpose other than to read that adjusting clockwise gave you a firmer shift and counterclockwise gave a softer shift (could have that backwards - do not remember). In fact I adjusted the vac modulator several times and do not recall feeling any vast change. And I think you are saying that the vac modulator clicker will adjust how much or how little vac it bleeds off when you downshift.
Clemson - your post sounds right and I think I just plumbed and compared the two extreme opposites - vac and zero vac.
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When you let off the accelerator the vac to the tranny increased.
I never considered that. I struggled to make my car up-shift without slamming gears and jerking the automobile but thinking back I remember it clunking when the transmission downshifted too. My vacuum was always low so I bought and installed a new pump.
Yes, the instructions I've read on adjusting the vac pressure for each shift point give lower vac pressures for higher engine RPM at each shift point. Those vac level are achieved by adjusting the VAC.