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I was overhearing a fellow at a Pontiac show South of Phoenix a couple of weeks ago... He had been describing how the switch pitch tc in his '65 or so full size Pontiac drops a few hundred RPM's after cruising at 65mph or so. I butted in and said no no no! I owned a '66 Skylark GS-401 ST300 (2 speed-Super Turbine, similar to a Powerglide) with the dual range torque convertor when I was 20 until last year (35 years). As an inquisitive kid I quickly figured out I could "fool" the tc into hi-stall by simply wrapping a twist tie around the micro-switch on the accelerator rods where it turned 80d from the firewall to the carb. I explained this to him, he was insistent that his rpm's would drop blah blah. I explained to him that he was describing the GM innovation introduced in 1980 (1979?). I just googled the lockup tc and found this info. I have (hopefully) attached a couple of screenshots of the page where I found a description of a turboglide tranny that had a variable pitch tc that gives the impression of a passing gear. So this guys car should have had a TH400 with a switch pitch tc, not the extinc Turboglide. I further described that the TH400 tranny switch pitch only does it's business at idle and just off idle PERIOD! I forget exactly what his car was, maybe a '65 Grand Prix like mine? I also have a '65 Buick Electra 225, both lo miles survivors, dead stock. I can't recall if my cars have the SP TC as I 've only owned them a short time. Both have TH400's. The website I got the screenshots from is crankshaftcoalition.com
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