Sonnax 34528-01K, 4L80E / 4L85E Reverse Servo Spacer Kit

The Sonnax reverse servo spacer kit 34528-01K is a simple, low-cost approach to increase the durability of GM 4L80-E and 4L85-E gearboxes while eliminating the need to install early-design reverse servo pistons into late units.

Because of a design change in 1996, the reverse servo piston frequently fails because it is more stressed than earlier servos. By extending the contact area between the aluminum piston and spacer and including a cushion spring washer, this Sonnax 4L80E reverse spacer kit minimizes piston stress. The new contact area is more than twice as large as the original, and the pressure between the piston and the spacer is 60% lower. Additionally, this Sonnax kit attaches effortlessly during assembly and requires no machining or other adjustments. Excessive line pressure in reverse is prohibited.

• Increased contact area reduces pressure between apply pin and piston by 60%
• Added Belleville spring washer reduces shock on piston
• No machining necessary, drop-in components
• Maximum durability for minimal cost