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Old 11-01-2017, 10:42 PM
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Diseasel300 Diseasel300 is offline
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Quote:
Originally Posted by tyl604 View Post
Loss of vac will not give you harsh upshifts. It is designed to bleed off vac immediately as you accelerate and give smooth upshifts with practically no vac. You will start off with about 15 IHG of vac and as soon as you hit the pedal it goes pretty quickly to zero. Technically there may be a little vac still there at upshifts but very little. On the flip side, it will downshift quite harshly with no vac.

I know from personal experience as I have hooked up the Mityvac between the VCV and the trans modulator on my '81 300SD and have tested it both with and without vac on upshifts and downshifts. My assumption of course if that your works the same way and I think it does.
Loss of vac WILL cause rough upshifts at part throttle. At low throttle input, the VCV will still be supplying vacuum to the modulator to soften the shifts. At half-throttle or more, the vacuum is bled off fully and the horsepower is sufficient to prevent a rough shift. The modulator is there for a reason, it is not just for smooth downshifting while coasting.
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