A/T - Binding or Inoperative In Reverse

91chevy16

GMC NUMBER: 91-7A-87

GROUP: 7A Automatic Transmission

DATE: April, 1991

CORPORATE
NUMBER: 977143R


SUBJECT: BINDING OR INOPERATIVE IN REVERSE, STUCK 4-3 SEQUENCE VALVE, AND/OR 2-3 SHIFT VALVE

MODELS: 1982-91 TRUCKS WITH 4L60 (700-R4) AUTOMATIC TRANSMISSIONS

THIS BULLETIN CANCELS AND REPLACES GMC TRUCK SERVICE BULLETIN
89-7A-115, DATED NOVEMBER, 1989 TO ADD 1991 MODEL YEAR TRUCKS AND INFORMATION CONCERNING THE BOLT TIGHTENING PATTERN. ALL COPIES OF 89-7A-115 SHOULD BE DISCARDED.


This bulletin covers service information for 1982 through 1991 HYDRA-MATIC 4L60 transmissions which may exhibit a binding in reverse condition. (The vehicle would feel as though the engine were being "brake torqued" if reverse range was selected.)

Figure 1 - Control Valve Assembly:

SERVICE PROCEDURE:
When servicing a HYDRA-MATIC 4L60 transmission for a binding in reverse condition, remove the control valve assembly and inspect the 4-3 sequence valve and the 2-3 shift valve. Refer to Figure 1. Either valve, if stuck in the upshifted position, will result in a binding condition. To correct this condition, the valve body must be completely disassembled and reconditioned according to procedures contained in the HYDRA-MATIC 4L60/THM 700-R4 Unit Repair section of the appropriate Service Manual. Inspect the transmission bottom pan for clutch material or burnedfluid. Evidence of this will necessitate further transmission diagnosis.


Repairs may include complete transmission reconditioning, including disassembly and reconditioning of the transmission pump and possible torque converter replacement. Complete the cleaning of the hydraulic circuit by changing the transmission fluid and filter and flushing the transmission cooler and cooler pipes.

Important

Figure 2:

Overtorquing or uneven torquing of the bolts during unit reassembly can cause valves to bind. This condition may become more apparent as the unit warms to operating temperature. The correct bolt torque specifications for the HYDRA-MATIC 4L60 control valve assembly are 8-14 N-m (6-10 lb.ft.). Torquing bolts to the minimum specification, 8 N-m (6 lb.ft.) is recommended. The bolts should be tightened in a spiral pattern starting at the center and working toward the outside of the control valve assembly as shown in Figure 2.