The 1st type 3-2 valve info in the '66 shop manual looks like data reused from the '65 manual. Unfortunately it doesn't indicate what the 2nd type is. Buick built both types (with and without the spring) in those early years of '64-67. Posts on other sites indicate some '67 units don't even have a 3-2 bore in the valve body. The spring was used to perform a part-throttle 3-2 downshift at speeds below 33 mph. The detent mechanism was not involved.
The '65 troubleshooting chart is clearer as it shows missing or broken spring as a cause of missing part-throttle downshifts (a symptom not shown in the '66 chart). Missing or broken spring is not shown under missing detent downshifts in the '65 chart.
Transmission nameplate codes for the 300 and 340 engines indicate the spring was used more in the small-block applications. So a 3-2 valve bore without a spring (typical for a Riviera) would not cause missing detent downshifts.
When the detent solenoid energizes, the detent oil pressure builds up and controls the valves that do the downshifts. The modulator oil supply is overridden during detent downshifts. So the modulator would not have an effect on detent downshifts.
Since the both the 3-2 and 2-1 detent downshifts are missing, it would be good to confirm 12V power is getting down to the transmission harness connector by using a test light.(Maybe you already did this.)
Bookmarks