August 18, 2017
A burnt band on the GM 4L60, 200-4R or 325-4L transmission can be created by accumulator cross leaks. A driveability complaint of 2nd gear starts or 2-3 bind-up can result from excessive piston wear. These complaints can be caused by oil cross leakage between the piston and pin in the 1-2 and 3-4 accumulators. This is due to the constant oscillating motion of the aluminum accumulator pistons on the steel pin.Band apply pressure is simultaneously sent to the accumulators and band.
The problem occurs when accumulator control oil and band apply circuits cross leak. Accumulator control oil will bleed into 2nd apply or 4th apply and drag the band/clutch due to imbalanced oil circuits. Ream the bore and install Sonnax oversized accumulator pin and reamer kit 77999 to resolve these problems.