A/T - Buzzing Noise On Engine Shutdown

NUMBER: 93-T-13

CORP.REF.NO: 277141, 277142

DATE: November 1992

SECTION: 7, 4L60, 4L60-E

SUBJECT:
BUZZING NOISE ON ENGINE SHUTDOWN - INSTALL NEW PRESSURE REGULATOR VALVE

MODELS/YEARS:
1991-92 CUSTOM CRUISER AND
1991-93 BRAVADA W/4L60 OR 4L60-E TRANSMISSION

CONDITION:
Some 1991-92 Custom Cruiser, and 1991-93 Bravadas equipped with the HYDRA-MATIC 4L60 or 4L60-E transmission may exhibit a buzzing noise coming from the transmission on engine shutdown.

CAUSE:
The buzzing noise may be a result of the pressure regulator valve oscillating due to oil pressure instability during engine shutdown.





CORRECTION:
A new pressure regulator valve has been released which will improve the oil pressure stability at lower RPM. Parts are currently available from GMSPO. This repair can be performed on a 1993 4L60-E prior to January 1, 1993 even though the pressure regulator valve is not included in the list of service parts available in Dealer Technical Bulletin 93-T-07.