Valve Body Checkballs

GMC NUMBER: 88-T-16

GROUP:7A - Automatic Transmission

DATE: May, 1987

CORPORATE
NUMBER: 867103
SUBJECT: PROPER LOCATION OF THE FORWARD CLUTCH CHECKBALL

MODELS: ALL 1987 LIGHT DUTY MODELS AND 1988 C/K MODELS WITH THM 700-R4

AUTOMATIC TRANSMISSIONS

FIGURE 1 - CHECKBALL LOCATIONS ON TRANSMISSIONS WITH AUXILIARY VALVE BODIES:

BULLETIN COVERS:

Service information on the correct location of the forward clutch checkball (#12-Figure No. 1) and the possible effects of installing the checkball in the wrong location.

FIGURE 2:

DATE OF PRODUCTION CHANGE:

By October 6, 1986 (Julian Date 279) (Figure No. 2) all 1987 THM 700-R4 transmissions were produced with an auxiliary valve body for an improved drive engagement shift feel. As part of this change, the lo and reverse #5 checkball located in the valve body assembly (Figure No. 3) was eliminated, and a new forward clutch checkball (#12-Figure No. 1) was added to the Auxiliary Valve Body. All 1987 Service Replacement Transmission Assembly (SRTA) units have this change.

FIGURE 1 - CHECKBALL LOCATIONS ON TRANSMISSIONS WITH AUXILIARY VALVE BODIES:

NOTICE:

1987 Service Manuals refer to the forward clutch checkball (#55B) in the auxiliary valve body as #5. To avoid confusion with the lo and reverse #5 checkball in a THM 700-R4 transmission produced without an auxiliary valve body (#55B-Figure No. 3), the forward clutch checkball has been changed to #12 (#55B-Figure No. 1).

FIGURE 3 - CHECKBALL LOCATIONS ON TRANSMISSIONS WITHOUT AUXILIARY VALVE BODIES:

SERVICE ACTION:

When servicing any 1982 through 1987 THM 700-R4 transmission without an auxiliary valve body (Figure No. 3), the lo and reverse #5 checkball (#55B) must be located in the control valve body.

FIGURE 1 - CHECKBALL LOCATIONS ON TRANSMISSIONS WITH AUXILIARY VALVE BODIES:

When servicing any 1987 THM 700-R4 transmission produced after October 6, 1986 (Julian Date 279) the forward clutch #12 checkball must be located in the auxiliary valve body (#55BFigure No. 1). Do not install a checkball in the control valve body.

NOTICE:

If the forward clutch #12 checkball is installed in either the valve body or over the orificed cup plug (359-Figure No. 1) in the auxiliary valve body, the following conditions can occur:

^ Delayed N-D, P-D or R-D
^ Harsh N-D, P-D Shifts
^ Slipping on Hard Accelerations
^ Forward Clutch Distress
^ No Upshift
^ 1-2 Tie-Up/Lo-Rev Clutch Distress and 2-4 Band Distress