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Old 04-25-2013, 02:58 PM   #46
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ATF Never changed in 135K Miles - Leave or Change it?


I didn't remember the term "switch pitch", but then there are a lot of things that I don't remember at my age. It appears that the "switch pitch" transmission was a special version of the turbohydromatic 400. I rebuilt a lot of those which probably included the switch pitch as well. The primary differences were in the valve body and a different sized shift solenoid. I usually identified the transmission by the id tag on the transmission or by the specifications provided by GM. The primary problem with repairing a transmission of this type would be identifying the unusual shift pattern when testing for proper operation since the downshift and upshift behaved differently from other th400s. Anyone who could rebuild a TH400 should not have had a problem rebuilding a "switch pitch".

Here is some additional info:
http://www.buickperformanceclub.com/SPTrans.htm

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Old 04-26-2013, 06:00 AM   #47
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ATF Never changed in 135K Miles - Leave or Change it?


That's only part of it. Another primary difference (biggest difference) was the torque converter, which is where it got the name "switch pitch". The stator blades can change the angle to reduce friction in order to put the vehicle in motion. The effect feels like a major torque increase at full throttle. Most people who rebuilt the Switch Pitch tranny's didn't know enough about them, and replaced the Switch Pitch converter with a regular lockup converter.

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