1988 THM 700-R4 TRANSMISSION NEW PRODUCT INFORMATION
Subject: THM 700-R4 TRANSMISSION - NEW PRODUCT INFORMATION
Model and Year: 1988 PASSENGER CARS AND LIGHT DUTY TRUCKS EQUIPPED WITH 1988 THM 700-R4 TRANSMISSIONS
This bulletin covers New Product Information and changes that have occurred on all 1988 THM 700-R4 transmissions used in passenger cars and light duty trucks.
SERVICE MANUAL REFERENCE:
Product changes in this bulletin that are included in your 1988 THM 700-R4 Unit Repair Service Manual are identified by an asterisk in the 1988 Unit Repair Table of Contents.
SERVICE NOTE:
SOME 1988 C/K TRUCKS WILL HAVE THE SAME TRANSMISSIONS USED IN 1987 MODELS. BEFORE SERVICING ANY 1988 C/K TRUCK, REFER TO THE TRANSMISSION IDENTIFICATION (FIGURE 1). 1987 TRANSMISSIONS CANNOT BE SERVICED WITH 1988 PARTS.
VEHICLE APPLICATIONS
1. New Control Valve Assembly All Models
A new Control Valve Assembly and Valve Body Spacer Plate are used for all 1988 THM 700-R4 transmissions to improve consistency for the 1-2 and 3-4 shifts. The new Assembly consists of revised 1-2 and 3-4 shift valve trains. With the change, the lo range downshift valve (321), lo range control sleeve (320) and the 1-2 lo range upshift valve (353) have been eliminated. Refer Figure 2.
NOTE: With the changes, the #9 Lo-Detent Checkball has been eliminated from 1988 THM 700-R4 transmissions (Refer Figure 3) . 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.
A 1988 Control Valve Assembly CANNOT be used on any past model THM 700-R4 transmission.
VEHICLE APPLICATIONS:
2. New Input Clutch Assembly Camaro and with 3-4 Clutch Boost Springs Corvette only
TRANSMISSION MODELS: YDM, YMM, YWM, and YZM
A new Input Clutch Assembly with 3-4 boost springs (600) was added to quicken the release of the 3-4 clutch on downshifts. Refer Figure 4.
When servicing these models the 3-4 boost springs must be installed, else improper shift timing can occur.
NOTICE: The 3-4 clutch boost springs CANNOT be use on any prior year THM 700-R4 transmission or any 1988 THM 700-R4 transmission other than the YDM, YMM, YWM or YZM models.
SERVICE PARTS INFORMATION:
Part Number Description ------- -------------------- 8667424 Spring Asm, Boost 3-4 Clutch (600) - (5 required)
VEHICLE APPLICATIONS:
3. New Reverse Input All models except S/T Clutch Piston Truck and MCM, MTM, PRM, TAM, TBM and YXM
A new Reverse Input Piston with a smaller bleed orifice (.95") has been added. (Note: The 1988 THM 700-R4 models MCM, MTM, PRM, TAM, TBM, and YXM will continue to use the ."6" orifice piston.) Refer Figure 5.
When servicing a 1987 THM 700-R4 (produced after Julian Date 040), transmission, except models MCM, MTM, PRM, TAM, TBM, and YXM models) replace the Reverse Input Clutch Piston with the new .095" orifice piston.
SERVICE PARTS INFORMATION
Part No. Description Identification ------- ----------------- -------------------------- 8663071 Piston - Reverse "All Stamp (.116" orifice) Input Clutch (MCM, MTM, PRM, TAM, TBM, And YXM Models Only)
8667841 Piston - (New) "B" Stamp (.095" orifice) Reverse Input Clutch (All Other Models)
VEHICLE APPLICATIONS:
4. Case Die Change - Slot At The All Models Lo and Reverse Case Hub
The slot, located in the case hub at the lo and reverse piston, no longer extends through the hub to eliminate the possibility of a bur on the inside edge of the slot from cutting the lo and reverse piston inner seal during installation. Refer Figure 6.
The change over of case dies began during late 1987 production and was completed early in the 1988 model year.
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 screw driver through the slot. With the new case, the slot does not extend through. To remove the lo and reverse piston with the new case, compress the lo and reverse clutch spring assembly and using Snap Ring Remover/Installer, Kent Moore tool number J-34627, remove the retaining ring.
NOTE: This material IS NOT included in your 1988 Service Manual Unit Repair Section.
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.
