Itching for a Switch Pitch Transmission

by George Nenadovich

Switch pitch(s.p.) transmissions were availabe from 1964-7 in the full size BOP cars. Even some Cadillacs have the s.p. transmissions. It is best to find the 1965-7 trans. as they are a little different than the 1964 versions. The name switch pitch comes from the vanes in the torque converter being able to change their angle (pitch) in order to reduce friction(force) and get the vehicle moving. This would be similar to somebody trying to start pedaling a ten speed in 10th gear versus 1st or 2nd gear. These transmissions were used in the full size cars since the engines did not make a lot of torque and they were quite heavy.

For instance, I pulled a s.p. TH400 and 430 engine from a 1967 Electra 225. When I took the car to the slavage yard, it still weighed in at 3600 lbs. With complete motor and trans, figure close to 5000 lbs.

The easiest way to identify the s.p. is by looking at the trans. pan. On the TH400, you will see 3 dimples and a shoe heel impression. The s.p. is also found in the ST300 trans. but are not common. The shoe heel impression is where the filter picks up fluid and the pickup is shaped just like a shoe heel.

The converter changed stall speeds from 1800 rpm to 2600-2800 rpm and used a 12" converter in the TH400 and an 11" converter in the ST300. You can interchange the converters. You will also see a switch on the throttle linkage near the carb where the throttle position will dictate the change in the two stall speeds via an electrical solenoid located inside the trans. Most people will remove the entire harness from the donor car and then use a toggle switch mounted on the dash to activate the s.p. converter.

The 1967 Electra 225, I pulled my s.p. from had a short shaft TH400 but most of the time the full size BOP cars will have the longshaft transmissions which is not desirable in the 1968-72 GM A-bodies. The best bet is to remove the entire trans. and then convert a shortshaft TH400 to the s.p. converter. All 1973-77 Pontiac Grand Prix cars have shortshaft TH400 and are quite common. If you know how to change the non-s.p. trans over, you can pull the pump, switch and solenoid out of the longshaft s.p. trans and then install it into the non-s.p. trans. That way you won't have to buy two transmissions from the salvage yard.

Aftermarket converters are still available and several companies can make a converter to order. Please see our Buick vendors page for additional info. Some additional info from that 1967 Electra 225 is the 430 had a center sump oil pan since it has an "X" frame. This center sump engine will not work in 1968-72 Skylarks since it will not clear the frame. You will need to find a rear sump BB(big block) from 1970-76 Electras, LeSabres and get the oil pan and pickup tube. The s.p. trans. bolts up just like the non-s.p. trans. If you have any questions, please e-mail. Good Luck!

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Changes last made on: 2-4-98