DELAYED PARK/NEUTRAL TO DRIVE SHIFT ENGAGEMENT
Model and Year 1981-89 CHEVROLET WITH THM 200-4R TRANSMISSION
This bulletin covers service and parts information for a new forward clutch housing and shaft assembly. The new assembly has a larger forward clutch feed orifice in the forward clutch shaft. The new forward clutch housing and shaft assembly may address a delayed drive engagement concern (refer to "Service Action"). There are no changes to the forward clutch die cast piston and clutch pack that were introduced with the neutral to drive (feed-bleed) garage shift package. (Refer to Dealer Service Bulletin 87-151, Section 7A, dated May, 1987.)
DATE OF PRODUCTION CHANGE: (Figure 1) ------------------------- August 24, 1988, Julian Date 237, the new forward clutch housing assembly introduced on all 1989 THM 200-4R models.
SERVICE ACTION:
The THM 200-4R "garage shift package" (refer to Figures 2 and 3) softens the Park/Neutral to Drive shift engagement feel by cushioning the apply of the forward clutch piston. The cushioned apply increases shift time, this does not indicate a transmission durability concern.
When diagnosing a delayed drive engagement concern, verify the apply time using a stopwatch and use the following guidelines to decide if service action is necessary:
1.5 - 2.0 second apply time ....... Normal apply time. The new housing assembly may not provide a decrease in apply time.
2.0 - 3.0 second apply time ....... The new housing assembly may decrease apply time by approximately .5 - 1.0 second.
3.0 or more second apply time ..... Inspect for other causes*of delayed Drive engagement. If no other causes are found, the new housing assembly will decrease apply time.
* Conditions which contribute to delayed Drive engagement:
- Improper Fluid Level - Cut Or Overlapping Teflon Seal Rings On Forward Clutch Shaft - Cracked Or Broken Forward Clutch Piston - Cut Or Rolled Forward Clutch Piston Seals - Porosity In The Center Support
If forward clutch housing replacement is necessary, use the chart under "Service Parts Information" for the appropriate service part number based on model year, build date and transmission model.
SERVICE PARTS INFORMATION:
Part No. Description Year - Models -------- ----------- -------------- 8639969 New Forward Clutch 1986 (built after Julian Housing Assembly Date 115) 6AAF,6ABF,6APF, 6CAF,6HFF,6KCF, 6KJF 1987 7CTF,7HFF,7KCF, 6KJF,7HDF 1988 8CTF,8KTF 1989 All
NOTE: Part Number 8639969 should be used to service the above models/years built with the "Garage Shift" package. All other models use part number 8639942 until current GMSPO stock is depleted.
8639970 New Neutral to Drive 1981-1982 All Models Shift Package - 1983 All (Except 3OZ Model) 1984 4AA,4AP,4BQ,4BY, Contains: New Forward 4HE,40G,40J,40M Clutch Housing Complete, 1985 5AA,5A0,5AP,5BQ, Front Internal Gear, and 5HE,50G,50J,50M Thrust Washer. 1986 6BRF
SERVICE PARTS INFORMATION:
Part No. Description Year - Models -------- ----------- ------------- (or the following models built before Julian Date 115) 6AAF, 6ABF, 6APF, 6CAF, 6HFF, 6KCF, 6KJF 1987 7BRF
Note: Part number 8639970 must be used when updating the above models/years to a Garage Shift package; should that option be desired. All other models being updated to a Garage Shift package, use part number 8639943 until current GMSPO stock is depleted.
Parts are currently available from GMSPO.
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.
