A/T - 4L80E Buzzing Noise
TECHNICAL BULLETIN # 139TRANSMISSION: 4L80-E
SUBJECT: BUZZING NOISE
APPLICATION: GM
4L80-E BUZZING NOISE
A complaint of a buzzing noise on a 4L80-E may be caused by pressure instability in the pressure regulator line-up. A service package (Part # 8682998) is available to correct this condition. Starting March 15, 1991 (Julian Date 074) all units were built with the new Pressure Regulator Assembly.
Mis-matching certain 1st and 2nd design components will cause uncontrollable line pressure. Use all 1st design components together, or preferably, all 2nd design components.