A/T - 125/125C Repeated Pump Rotor Spline Failure

TSB 87-33 (May)

SUBJECT: 125/125 C

PROBLEM: Repeated pump rotor spline failure

SOLUTIONS:




1. Always check side clearances when replacing a pump rotor. With a straight-edge across the pump body, proper clearance to the rotor is .0026" to .0036". Clearance from the outside of the pump rotor to the inside of the pump slide should be at least .005". If it is not, grind approximately .003" to .005" from the outer area of the pump rotor (grind the black area off). See Figure 1

2. Replace the rubber seals for the pump slide. These seals tend to "flatten out" with age, which many cause unnecessary slide movement.

3. Always use hardened pump rotors when replacement is necessary.

4. Use the late type pump rotor and pump driveshaft when replacing them. Both have 15 teeth instead of the 20 teeth found on the early type.




5. Grind the second land off of the pressure regulator valve. If the pressure regulator valve has no hole, grind a 1/8" flat on the first land also. See Figure 2.

6. To give more spline contact, flip the pump rotor upside down (recess for rotor guide facing opposite direction), discard the guide in auxiliary valve body cover, and install a teflon sealing ring on the pump driveshaft.




When installed, this teflon sealing ring will be between the flange on the pump driveshaft and the bearing in the valve body. See Figure 3.

This sealing ring should not damage the metal clad seal found on THM 125 C transmissions.

It is the rear primary sun gear sealing ring in the T-35 transmission, part # 3176130.