A/T - New Product Information
88chevy02GMC NUMBER: 88-T-68
GROUP: 7A - Automatic Transmission
DATE: January, 1988
CORPORATE
NUMBER: 877106
SUBJECT: NEW PRODUCT INFORMATION
MODELS: 1988 LIGHT DUTY MODELS EQUIPPED WITH THM 700-R4 AUTOMATIC TRANSMISSIONS
BULLETIN COVERS:
New Product Information on all 1988 THM 700-R4 transmissions. The information contained in this bulletin describes changes that have occurred in the 1988 THM 700-R4 transmission. Refer to each section of this bulletin for specific product change information.
FIGURE 1 - 700-R4 TRANSMISSION IDENTIFICATION INFORMATION:
DATE OF PRODUCTION CHANGE: (Figure No. 1)
Beginning with the Start of Production 1988, all 1988 THM 700-R4 transmissions were produced with the product changes listed in this bulletin.
SERVICE MANUAL REFERENCE:
Product changes in this bulletin are included in your 1988 THM 700-R4 Unit Repair Service Manual and are identified by an asterisk in the 1988 Unit Repair Table of Contents.
SERVICE NOTE
SOME 1988 C AND K TRUCKS BUILT PRIOR TO SEPTEMBER, 1987, WILL HAVE THE SAME TRANSMISSIONS THAT WERE USED IN OTHER 1987 MODELS. BEFORE SERVICING ANY 1988 C OR K TRUCK, REFER TO THE TRANSMISSION IDENTIFICATION. THE 1987 TYPE TRANSMISSIONS CANNOT BE SERVICED WITH 1988 PARTS.
SUBJECT: VEHICLE APPLICATIONS:
New Control S/T, R/V, C/K, G and M
Valve Assembly
FIGURE 2 - 1988 MODEL CONTROL VALVE ASSEMBLY:
CHANGE TO ASSEMBLY COMPONENTS:
(Figure No. 2)
A new Control Valve Assembly and Valve Body Spacer Plate for all 1988 THM 700-R4 transmissions. The new Control Valve Assembly consists of revised 1-2 and 3-4 shift valve trains. With the change to the 1-2 valve train, two valves and one sleeve have been eliminated. The lo range downshift valve, the lo range control sleeve and the 1-2 lo range upshift valve have been eliminated from the 1988 THM 700-R4 Control Valve Assembly. These new valve trains improve consistency for the 1-2 and 3-4 shifts.
With the changes made to the control valve assembly, the #9 Lo-Detent Checkball has been eliminated from 1988 THM 700-R4 transmissions.
FIGURE 3 - 1988 MODEL CHECK BALL & OIL SCREEN LOCATION:
SERVICE ACTION: (Figure No. 3)
A 1988 Control Valve Assembly CANNOT be used on any past model THM 700-R4 transmission. In addition, when servicing a 1988 THM 700-R4 transmission, DO NOT install a #9 checkball in the case. Installing a #9 checkball in a 1988 model case could cause the lo and reverse clutch to burn.
SERVICE MANUAL REFERENCE:
This material is included in your 1988 Service Manual Unit Repair Section. All material that is new for 1988 or was not included in your 1987 Service Manual is noted by an asterisk in the 1988 Unit Repair Table of Contents.
SUBJECT: VEHICLE APPLICATIONS:
New Reverse C/K, R/V, G and M
Input Clutch Piston
TRANSMISSION MODELS:
All (Except: MCM, MTM, PRM, TAM, TBM and YXM)
FIGURE 4 - REVERSE INPUT CLUTCH ASSEMBLY:
CHANGE TO ASSEMBLY COMPONENTS:
(Figure No. 4)
A new Reverse Input Piston (607) with a smaller bleed orifice (.095") has been incorporated on all 1988 THM 700-R4 transmissions (except models listed above). (Note: The 1988 THM 700-R4 models MCM, MTM, PRM, TAM, TBM, and YXM will continue to use the .116" orificed piston.)
SERVICE ACTION:
When servicing a 1987 THM 700-R4 (produced after Julian date 040) transmission, (except
MCM, MTM, PRM, TAM, TBM, and YXM models) replace the Reverse Input Clutch Piston with the new .095" orificed piston.
SERVICE PARTS INFORMATION:
SERVICE MANUAL REFERENCE:
This material is included in your 1988 Service Manual Unit Repair Section. All material that is new for 1988 or was not included in your 1987 Service Manual is noted by an asterisk in the 1988 Unit Repair Table of Contents.
SUBJECT: VEHICLE APPLICATIONS:
Case Die Change - S/T, C/K, R/V, G and M Slot At The Lo And Reverse Case Hub
FIGURE 5 - LO AND REVERSE CASE HUB SLOT:
CHANGE TO ASSEMBLY COMPONENTS:
(Figure No. 5)
The slot located in the case hub at the lo and reverse piston no longer extends through the hub. The change in the case eliminates the possibility of a burr, on the inside edge of the slot, from cutting the lo and reverse piston inner seal during installation.
DATE OF PRODUCTION CHANGE:
The case dies began change over during late 1987 production and were completed early in the 1988 model year.
SERVICE ACTION:
When servicing the lo and reverse piston on 1987 and prior model transmissions it was possible to remove the lo and reverse clutch retaining ring with a screwdriver through the slot. With the new case change, the slot does not extend through the case hub so the retaining ring is not accessible with a screwdriver. To remove the lo and reverse piston, compress the lo and reverse clutch spring assembly and using Snap Ring Remover/Installer, Kent Moore tool number J-34627, remove the retaining ring.
SERVICE MANUAL REFERENCE:
This material is NOT included in your 1988 Service Manual Unit Repair Section.