NO UPSHIFT CONDITION AFTER DOWNSHIFT AUTO. TRANSMISSION

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

This bulletin cancels and supercedes Chevrolet Dealer service Bulletins 86-42 (Section 7A) dated March 1986 and 86-42 Reissue (Section 7A) dated July 1986. All copies of both bulletins should be destroyed to prevent confusion.

Some 1984 through 1986 THM 200-C or 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 remains at a boosted level, resulting in a no upshift condition.

To repair this condition, a new throttle valve plunger, throttle valve bushing, and for some models a throttle valve lever and bracket assembly should be installed. Refer to Figures 1 and 2 for transmission nameplate identification information and to Figures 3 and 4 for service parts identification. Chart A provides service package part numbers, transmission model applications and 1986 model start of production Julian dates for the THM 200-4R and THM 200-C transmissions.

1986 ** TRANSMISSION MODEL AND YEAR MODEL SERVICE PACKAGE JULIAN PART NUMBER TRANSMISSION DATE 1986 1985 1984 ----------- ------------ ---- ---- ---- ---- 8639940 THM 200C N/A JY CZ,JY

8639932 THM 200C 062 CAB,CUB CS,CO,CV C5,C6

8639935 THM 200-4R 057 CAF,CHF CH,CQ,CR CQ * CRF,CZF CY

8639939 THM 200-4R N/A CR

CHART A

* Service package contains (1) throttle valve plunger, (1) throttle valve plunger bushing, and (1) throttle lever and bracket assembly.

** 1986 Model Julian date begins in calendar year 1985

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.