Try making a constant 2 inches of vacuum to the trans and drive it again. If the shift is okay, firm'ish but no flare then you need to adjust the vacuum control valve on the i/p to mimic 2 inches at part throttle.

If the restrictors in the supply of vacuum to the shift circuit are missing or too big you'll never get the shifts right because the vacuum valve can only bleed off so much vacuum signal . High vacuum volumn makes for soft shifts and often flare.

Steve Brotherton wrote the definitive paper on transmission vac' control and adjustment..read it all, it's very enlightening. Go to this page and click on link 'MAGAZINE Articles'..........

http://www.continentalimports.com/ser_index.html


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