Designed for GM 4L80-E and 4L85-E racing transmissions, Sonnax externally adjustable servo kit 34914-28K makes low/reverse band maintenance quick and easy. It’s an ideal way to improve reliability and make staging more consistent and predictable.

Checking L/R band adjustment after repeated use is good practice. Vehicles with a transbrake rely on the L/R band applied by the L/R servo to prevent the car from moving during staging — critical for proper launch. If the servo is out of adjustment, the servo piston can bottom out in the case bore and the band may not hold. This prevents full apply of the transbrake and causes the vehicle to creep forward. Unfortunately, OE servos with steel covers are difficult to adjust in vehicle, so a quick check with such a servo installed is impractical for most racers.

The improved design of the Sonnax externally adjustable servo makes checks and adjustment of the L/R servo easy. There is no cover or access plug to remove because the adjuster itself extends through the cover. A quick check is done simply by pushing on the end of the adjuster and observing the movement of the piston relative to the servo cover.

• Quickly check and adjust the low/reverse band to prevent transbrake malfunction
• Unique servo cover and adjuster design makes in-vehicle band service easy
• Works with or without OE 1-2 accumulator piston
• 6061 Anodized billet aluminum piston and cover