(50% OT) Switch Pitch Super Turbine 400 Trans
I just bought two of this rare transmissions and they are SO KOOL. These 3 speed autos' were built for Buicks, Olds, and Rolls Royce (& most likely a few others) for only 3 years, from 1964 through 1967 and are the processor to the TH400. They share the same internal components with the newer TH400 but they are very different in one way,,,,,,,,the vanes in the torque converter are adjustable with the flip of a 12volt switch.
These ST400's have a special fluid pump, input shaft and torque converter. When the trans is in "normal", low stall mode, the pump and vanes work like a typical, stock converter with a 1800rpm stall(actually, a bit "loose" for todays stock converters). When 12 volts is applied to the pumps servo, some of the fluid is redirected through a hole in the center of the trans input shaft, into the converter. The vanes in the torque converter are mounted on pivots with a cam type level attached to each vane. The fluid acts with another servo in the converter to change the pitch of the vanes, increasing the stall speed to 2200rpm. You basically have a converter with a street stall or a race stall,,,,,,,with the flip of a switch !!!! .
In the original cars, a plunger type switch was setup on the throttle cable. As the car was at idle, the switch was "on" and it was in high stall. This would keep the car from wanting to "creep" at stop lights,,,,,,,,you need to consider that the motors in these cars had 465lbs or torque @ about 2000rpm and the idles were set at 500rpm, very powerfully motors. As soon as the throttle was depressed, it switched to low stall.
The first trans will be going into my '77 Corvette. This trans was rebuilt by "TransGo" and a shift kit, extra clutches, etc. A custom converter is being built by P.A.E. with a 1300rpm low stall and a 3000rpm high stall,,,,when in high stall, the converters torque multiplication is twice that of low stall. There will be a microswitch on the throttle to kick it into high stall at idle, this will allow the use of a very "lumpy" race cam without stalling the motor at stop lights. Another switch will be a completely manual override, mounted to the shifter. This way, when I feel "the need", I can launch in high stall and hold it to about 4500rpm before switching to low stall. I will eventually wire it to one of the rev limiter functions on Jabcobs Mastermind control box for the nitrous system that I use,,I plan to program it to switch from high stall to low stall at a predetermined rpm, with a street mode setting and a race mode setting.
Now for the 4x4 stuff,,,,,,,,,,,,The combo I'll be using is a the ST400 to a NP203 overdrive box to a Atlas 4.3 . This will give reductions of 1 to 1, 2 to 1, 4.3 to 1 and 8.6 to 1 , plus the converters torque multiplication. This creates the problem of stopping,,,,,low stall converters are needed for very low speed crawling and compression braking (1100rpm stall) but they don't want to release when you need to stop in super low reductions. I'll be using a inline pressure switch in the brake line to kick the converter into high stall at set brake line pressure, this will still allow the brakes to slow me down without completely disengaging the trans,,,,but also disengage the trans if the brakes pushed hard enough to stop or are being lockup. I'll still be able to "double peddle" the gas and brake at low speed climbing/crawling. I'll also have a over-ride, manual switch to select high or low stall for mud race'n, sand drags and general screw'n around.
Let me know if you can think of any other advantages I could make happen with this trans.
It should be a fun experiment [img]images/graemlins/beach.gif[/img]