A/T - No Upshift

91chevy09

Number: 86-42


Section: 7A


Date: Mar., 1986


Subject: NO UPSHIFT CONDITION AFTER DOWNSHIFT


Model and Year: 1984-1986 THM 200C, 200-4R


AUTOMATIC TRANSMISSIONS


TO: ALL CHEVROLET DEALERS


A 1984 through 1986 THM 200-C, THM 200-4R transmission may exhibit a no upshift condition after a part or full throttle downshift.


This condition may be caused by internal leakage hydraulically locking the throttle valve plunger. If this occurs, the line pressure remaing at a boosted level, resulting in a no upshift conditlon.

FIGURE 1 - THM 200C TRANSMISSION NAMEPLATE:

FIGURE 2 - THM 2004R TRANSMISSION NAMEPLATE:

FIGURE 3 - TYPICAL 200C CONTROL VALVE ASSEMBLY:

FIGURE 4 - TYPICAL 200AR CONTROL VALVE ASSEMBLY:

To repair this condition, a new throttle valve plunger and throttle valve bushing should be installed. Refer to Figures 1 and 2 for transmission nameplate identification information and to Figures 3 and 4 for service parts indentification. The chart provided indicates service package part numbers, transmission model applications and 1986 model start of production Julian dates for the THM 200C and 200-4R transmissions.


IMPORTANT: This bulletin covers only those THM 200C, THM 200-4R transmission models that have the new service parts currently available. Additional information will be provided for those THM 200C, THM 200-4R models not covered in this bulletin, when the parts are available for service.