Whether you prefer your Pontiac be equipped with an automatic transmission or a manual, nothing feels better than a positive high-rpm upshift into Second gear that chirps the tires while accelerating at full throttle. It’s easily achieved with a manual transmission since the driver can upshift at any desired rpm, but automatics are considerably different.
An automatic transmission is designed to upshift automatically at a preprogrammed engine speed. The full-throttle shifts from the Turbo 400 in our ’72 Firebird have always occurred at a very low rpm. We remedied this by shifting manually at much higher speeds during spirited driving, but we thought leaving the selector in Drive and letting the transmission shift for itself would be much more consistent, and might reduce overall wear.
[1] The governor within an...
[1] The governor within an automatic transmission is responsible for full-throttle upshifts. The small weight and springs can be modified or replaced to increase or decrease the engine rpm at which shifts occur. TCI Automotive can provide new replacements for most any of those shown here should you find your original is damaged or worn.
TCI Automotive offers a Governor Recalibration Kit that’s designed to allow owners to adjust full-throttle upshift speed of any Turbo 350, Turbo 400, or 700-R4 transmission. We decided to use one to modify our Turbo 400’s governor and improve its performance feel on the street. It took us a few tries over the course of a weekend to get the shifts exactly where we wanted, but we accomplished it, and here’s how!
Our ’72 Trans Am is equipped with its numbers-matching 455 H.O. engine and code-PQ Turbo 400. When new, the transmission was likely programmed to upshift just past 5,000 rpm at full throttle. It had already been modified by the time we purchased it, and the Second- and Third-gear upshifts both occurred just beyond 4,000 rpm. The shift speed prevented the large-cube Pontiac from winding out in each gear, and that significantly limited acceleration and overall feel on the street.
[2] TCI Automotive offers...
[2] TCI Automotive offers this Governor Recalibration Kit that allows for quick and predictable governor adjustments. Part no. 326500 retails for about $55 and is readily available from a variety of sources.
After trying another Turbo 400 governor that had shifted much higher in its original application without any luck, we decided the best way to increase the shift points was to modify the existing governor. TCI Automotive’s Governor Recalibration Kit (PN 326500) includes a number of weights and springs, and allows an owner to fine-tune the transmission shift points. It sells for $55 and is available directly from TCI or through any number of mail-order retailers. Ours was to us within a couple of days.
Before performing any modifications to the governor, we first needed to determine exactly where our Turbo 400 was shifting in Drive. We found an open, unpopulated area where we could drive the car without worrying about colliding with other motorists or pedestrians. We strongly recommend that you do the same!
[3] On a Turbo 400, the governor...
[3] On a Turbo 400, the governor is located behind a stamped-steel plate on the passenger side. Be prepared for transmission fluid to drip out as its four bolts are removed using a 1⁄2-inch wrench. It’s a good idea to clean the entire area with solvent before removing the cover to prevent any dirt or grime from entering the transmission.
Wheelspin and/or accelerating uphill or downhill can also alter how quickly the engine revs, subsequently affecting upshift speed by about 100 rpm. A flat surface will yield the most accurate results. We found a suitable stretch of flat road and came to a complete stop. We then rolled into the throttle until it was wide open while closely monitoring the tachometer. The full-throttle shift into Second gear occurred at 4,100 rpm.
Since its impractical to find an open area where you can wind out your Pontiac through First and Second gear, we found an open stretch of highway where we could floor the accelerator pedal while traveling at about 50 mph. As expected, the engine kicked down into Second gear and the upshift into Third gear occurred at about 4,300 rpm. With a solid baseline established, we recorded these numbers and headed to the garage.
Past chassis-dyno testing has revealed that our Trans Am’s 455 H.O. reaches peak horsepower around 4,800 rpm. Most racers will tell you that shifting about 10 percent past the horsepower peak yields best performance. Considering our 455 H.O. still uses stock cast rods and the Trans Am spends all its time on the street, we decided that a full-throttle upshift speed around 5,200 rpm would provide strong performance without risking engine reliability.
[4] With the cover removed,...
[4] With the cover removed, the governor is easily accessible. We gently pulled it out of the transmission by hand, carefully twisting it counter-clockwise during the process.
[5] We clipped off the flattened...
[5] We clipped off the flattened ends of the original weight axles using sturdy wire cutters. The TCI kit includes new axles, so the originals can be discarded.
[6] We simply lifted the original...
[6] We simply lifted the original weight assembly out of the governor.