A/T - No Upshift Condition After Downshift

Number: 86-169

Section: 7A

Date: Sept. 1986
SUBJECT: NO UPSHIFT CONDITION AFTER DOWNSHIFT


MODEL AND YEAR: 1984-1986 THM 200C, 200-4R AUTOMATIC TRANSMISSIONS


TO: ALL CHEVROLET DEALERS


This bulletin is being issued to clarify service package part numbers which 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.

FIGURE 1 - THM 200-4R TRANSMISSION NAMEPLATE:

FIGURE 2 - THM 200C TRANSMISSION NAMEPLATE:

FIGURE 3 - TYPICAL 200C CONTROL VALVE ASSEMBLY:

FIGURE 4 - TYPICAL 200-4R CONTROL VALVE ASSEMBLY:

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