66 powerglide adjust shift point
I am working on a 66-327 300hp with a stock powerglide transmission. The engine had a Holley "list" 1850-2 carb which I replaced with a fresh Holley "list" 3230 carb. Before making the carb swap the transmission worked fine, transmission upshifted (first to second) under normal light acceleration at about 15 mph. After the carb swap the up shift occurs at about 25 mph under normal light acceleration. I think (not 100% sure) the transmission modulator vacuum was pulled from the top of the front metering plate using the 1850 carb, with the distributor vacuum taken from the carb base. Now, using the 3230 carb, transmission modulator vacuum is taken direct from the intake manifold via a two port fitting which also supplies power brake vacuum. I have not made any adjustments to the kick down linkage after swapping the carburetors. What steps must be taken to get the upshift point down to 15 mph? Also, can the transmission be damaged by driving the car without correcting the shift point? I'm hoping the adjustment is fairly straight forward as everything worked fine before my attempt to make the engine more "correct". Very much appreciate any comments / suggestions to help me trouble shoot this situation!
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Re: 66 powerglide adjust shift point
The late shift issue is still being investigated. It seems either the modulator is getting too much vacuum or too little vacuum. Would an increase in vacuum to the modulator cause the shift from 1st to 2nd to be later or earlier? I understand that the modulator may have an adjustment that could shorten the shift interval but its effect on shift interval is very limited? How is the modulator adjusted and would the change in shift point be significant after adjusting?
Does the mechanical kick down linkage adjustment have any effect on the shift point from 1st to 2nd? If so, should the rod be extended or shortened to reduce the shift time between 1st and second?
Appreciate all suggestions. Thank you in advance for your research.
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