switch pitch tranny

[bebop138]

What years did the switch pitch tranny get used, and these were the ones where you had to use the correct flex plate ie; balancing. I have a 425 and I want to make sure I use the correct tranny. Will this engine fit in my 57 Special using the stock motor mounts ( engine only ) will make new crossmember mount for the tranny later, just want to make sure that the boss holes on the engine will match my 57 mounts?? Thanks!!

[NTX5467]

The SP Turbo400s used a special torque converter and matching front pump, plus the appropriate switching to activate the "SP" (i.e., "low stall", "high stall") feature as it was desired. Many toggle-switched it rather than do the throttle linkage switches as the OEM production units had. Not sure about flywheels/flexplates . . . but . . . I suspect the difference in the SP T400 flex plate and the non-SP T400 flex plate (for the same engine) might have to do with the bolt circle and number of bolts holding the converter to the flywheel as both would have to "balance" the same -- if they are in fact different. I don't recall the need to change the flywheel when adding the SP converter/pump duo being mentioned in the magazine articles (back then).

As I recall, the ST300 (2-speed automatic) was a switch pitch also?

Enjoy!

NTX5467

[bebop138]

More questions if I may---the switch pitch was basicially passing gear? Do you need to hook up the wiring for the tranny to work? Are the torque converters and rebuild kits still avaliable? Were all the 401-425 in the Riv`s SP400? Thanks

[NTX5467]

"Switch Pitch" varied the torque multiplication ratio in the torque converter by changing the stator angle in the torque converter (i.e., "high stall", "low stall"). It was not a "gear" as such. All of the "mechanical gears" were still in the main case of the transmission.

The wiring has to be in place for the converter to work as designed. I'm not sure what the "default" mode might be if everything's there and not having electrical power to it.

Switch Pitch was an "upper carline" item, as in Olds and Buick and possibly Cadillac and NOT production equipment on Chevrolets and Pontiacs.

Hope this might help a little ...

NTX5467

[55PackardGuy]

Back to part of the original question, I'm curious what years the SP option was offered. Was it standard on any models? Sounds like it was an off-the-line enhancement that would help for big heavy cars--and stoplight grandstanding.

[NTX5467]

Not an "option", but "standard equipment" on the Turbo 400s in Buicks and Oldsmobiles and (possibly, as mentioned) Cadillacs and Buick's "Super Turbine 300" 2-speeds. Most probably 1964 (the first Turbo 400) until about 1966 or 1967--basically when the earlier Dynaflows and Hydramatics ceased to be in the model lineups in BOC cars.

The "Switch Pitch" was billed, as I recall, in the advertising as an advancement in power and efficiency (kind of an extension/adaptation of the variable pitch stator in the Dynaflow "torque converter" principle into a Simpson Step-Gear automatic transmission with a "normal" torque converter), but when it was discontinued, I recall the "improvements" for that year (when the SP was deleted) noted that the automatic transmission was "improved" to operate cooler.

Enjoy!

NTX5467

[Fr. Buick]

For some reason, the '64 turbo 400 in Buicks did not get the switch-pitch. It came a year later in '65.

There is a great book that gives all the details on this - "How to Work with and Modify the Turbo Hydra-Matic 400 Transmission" by Ron Sessions. Call Classic Motorbooks at 800-826-6600.

Happy wrenching,

Doug Cook

[The Old Guy]

One of the big advantages of the SP was that ,if the switches all operated as they were designed, the convertor would kick into high stall at idle. This kept the car from creeping so much at the stop.The minute the accelerator was depressed, it went back to low stall until the pedal was pushed far enough to hit the kick down. It was really an ingenious system.

The SP400 used the same flex plate as the standard TH400

Some drag racers used the convertor from the SP 300, for the extra RPM off the line, but it was too much for regular street use

[55PackardGuy]

So I had a "Switch Pitch" TH400 in my '65 Electra--and never even knew it! That car did feel remarkably "light" off the line considering its massive weight. That was one of the really fun things about it, it didn't feel like a big car but moved and handled in a way that made you think you were driving a little rocket.

[Guest brh]

You are correct the super turbine 300 two speed is a switch pitch for 65. My Skylark has it along with posi rear and the high performance 300. Its not a rocket from the line but if you punch it at about 40mph it will almost put ya in the back seat. Quite an impressive little car all stock.