A/T - 125/126C No Second Gear Or Slipping After Rebuild

TSB 86-4 (Jan)

SUBJECT: 125/126 C

PROBLEM:
No second gear, or second gear on rack only, or slipping second gear after rebuild.

CAUSE:
Loose band adjustment




Band adjustment should be 1/8" - 3/16" stroke. When the servo pin moves about 1/4" inward from the release position, the spring retainer (washer) will bottom against the case. (Figure 1). When the retainer hits the case, all further servo movement is merely compressing the servo spring, and will not force the pin any further.




Large variances in adjustment are occuring between one band/drum combination and another. Adjust with different length pins (Figure 2). Many times even longer pins are needed, and a good welder can weld more length onto the band end of the pin. Care must be taken not to get the pin excessively hot. Shape the band end properly with a grinder or file, and smooth the end with a wire wheel and/or sandpaper.

The servo piston inner oil seal (Figure 1) is of various sizes and will wear. Therefore, carefully check fit each ring in its bore. This seal is often worn because of a rough finish of the bore in the servo cover. Polish the bore, and replace the ring.




REMINDER:
Use correct 3rd accumulator check valve (Figure 3)

GM Part # 8643964