By Mike Bumbeck
Photos courtesy B&M Racing & Performance Products

ine-tuning your engine-transmission and rear gear combination for peak power delivery and consistency can mean the difference between going rounds, and rolling back on the trailer. A few hundred extra or a couple hundred less rpm on full throttle up shift can help keep your power band in the sweet spot for maximum horsepower and torque.

In TH-350, TH-400, and 700-R4 automatic transmissions, a governor controls part and full throttle up-shifts. Think of the governor as a hydraulic speedometer, which tells the transmission when to shift up based on vehicle speed. The governor turns in direct relation to the output shaft rotation, and therefore vehicle speed. Inside the governor is a valve that opens and closes to "govern" the upshifts.

There are two sets of rotating weights in the governor. The heavier, outer weights act at low vehicle speed and the lighter inner weights take over at higher speeds, especially during full throttle conditions. Centrifugal force acting upon the weights controls the opening and closing of the governor valve itself. The valve controls governor pressure delivery, which in turn controls upshifts.

When there is enough centrifugal force upon the weights to open the valve, line governor pressure overrides the shift valve spring, and the shift occurs. Changing the inner weights on the governor allows you to adjust the rate of this line pressure versus vehicle speed balancing act, and optimize full throttle shift points to your vehicles power to weight ratio, rear end gear ratio, and so on.

Since the governor came set from the factory for whichever vehicle the transmission originally came in, you may or may not be getting the most out of your setup. This is especially true if you have changed rear end gear ratios.

The B&M Governor Recalibration Kit allows for raising or lowering of transmission shift points relative to vehicle speed. Keep in mind that the governor has no effect on the crispness or "hit" of the shifts. Modifications to shift characteristics must be made by modifying the valve body with a shift recalibration kit.

The first step in modifying your shift points is to set a baseline. Record full throttle shift point rpm and vehicle speed. Use this first measurement for comparison to each change made in the weights or springs of the governor. In general, lighter weights bring later upshifts, while heavier weights will bring them earlier. Stiffer springs will produce stacked, closer shifts where as weaker springs tend to space shifts apart.

After each change record shift and speed information again before making the next adjustment. It is also possible to source a second governor assembly from a salvage yard or trans shop. In this way you can have a second unit ready to swap in, or keep an extra for street use and specific track conditions.

The first step in adjusting the governor is to get the governor out of the transmission. The governor can be removed with the transmission in the car. In a TH-400 remove the four bolts holding the cover assembly. Remove the cover then governor itself by pulling out and turning 1/8 turn counter clockwise. In a TH-350, and 700-R4 first remove the cover clip, and the governor itself.

The location of the governor on a TH-350 is behind this cover. For TH-400 and 700R4 the location is the same, but the cover is held in by four bolts. Allow time for transmission to cool before starting work. The heavier outer weights will not be replaced. Note the smaller inner weights and springs. These are what can be recalibrated. It is recommended that only ONE change be made at a time. Replace either weights, or springs, but not both.

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