Downshifting For Performance

Any hobbyist familiar with automatic transmissions knows the acceleration rush that occurs after applying heavy throttle while cruising at low speed. This action typically creates a mechanical symphony as the secondary barrels open, the transmission downshifts, and the speedometer and tachometer sweep clockwise. But if a Turbo 400 was transplanted into an older Pontiac without installing some type of kickdown switch, a large part of the fun could be missing.

The most common three-speed automatic transmissions used in performance applications today are the Turbo 350 and Turbo 400. Both are strong, reliable units that are internally calibrated to up-shift in a predetermined range based on a combination of engine load and speed. And they are also designed to downshift when conditions require additional engine speed to maintain vehicle speed or more commonly, when we stab the throttle to accelerate briskly.

As similarly as the two transmissions function, there is a significant difference in the way downshifts occur. The Turbo 350 kickdown function is mechanically operated via a cable mounted on the intake manifold near the carburetor. When the throttle linkage reaches a specific point, the cable triggers a mechanical detent valve inside the transmission--allowing it to shift into a lower gear. The Turbo 400 uses an electric switch to trigger a detent solenoid on the valve body to produce the same effect. It seems that either system works equally as well and neither is typically failure prone.

When the Turbo 400 began reaching production models in the late '60s, its kickdown switch was mounted on or near the carburetor. It was, however, relocated to the passenger compartment and mounted on the throttle pedal in later years. Any hobbyist who transplants a Turbo 400 into an older Pontiac originally equipped with another transmission must also install some type of kickdown switch, or proper downshifts cannot occur. This is the exact situation '64 Catalina owner Bill Schwanz had before him.

Schwanz purchased his Catalina convertible in the early '90s and promptly set out to rebuild its original engine and transmission. But during disassembly, he found the original 389 block was cracked. With his intentions aimed more toward cruising than a concours restoration, Schwanz located a 400 engine and Turbo 400 from a '74 Pontiac and had those installed. Although the transplant was successful, the lack of a kickdown switch left a large void in how it felt on the street.

Follow along as we install an aftermarket kickdown switch kit and give this Pontiac an attitude adjustment.