PARK/NEUTRAL TO REVERSE SHIFT FEEL (REPAIR DESCRIBED

MODELS: 1981-88 TRUCKS W/400/475 TRANSMISSION

This bulletin cancels and replaces GMC Truck Service Bulletin 88-T-116, dated June, 1988, all copies of which should be discarded. Case replacement for 1981 through 1986 model years is added to previous information.

BULLETIN COVERS:

Section I contains service parts information concerning park/neutral to reverse engagement shift feel on 1987-1988 vehicles with a GVWR of 10,000 lbs and under.

SectionII contains service parts information for case replacement on all 1981-1986 transmissions. The service case is the same as described under Section I except the orifice cup plug and checkbar are not required. This change will not correct a harsh reverse engagement shift feel on 1981-1986 transmissions.

SECTION I

TRANSMISSION APPLICATIONS:

1987 through 1988 THM 400/475 HYDRA-MATIC 3L80/3L80-HD

TRANSMISSION MODELS:

FDA, FFA, FMA, FTA, FWA, FZA, LKA, LMA, LTA, LUA, LWA, LZA, FJA, FNA, FPA, FUA, FYA, LBA, LDA, LHA, LJA, FCA, LFA, LRA, LSA, LCA

SUBJECT: ------- Park/Neutral To Reverse Shift Feel 1987 Thru 1988 Model Years

VEHICLE APPLICATIONS:

1987-1988 C, K, R, V Trucks 1987-1988 G Van (GVWR of 10,000 lbs and under)

SECTION I COVERS:

Service and parts information concerning park or neutral to reverse engagement shift feel on vehides with a Gross Vehicle Weight Rating (GVWR) of 10,000 lbs. and under. Included are: Control Valve Assembly, Valve Body Gaskets, Valve Body Spacer Plate, Case Assembly with an additional Checkball and Orifice Cup Plug.

NOTICE: The new Case Assembly, Control Valve Assembly, Gaskets, and Checkball will be included on all THM 400/475/HYDRA-MATIC 3L80/3L80-HD models. However, only the vehicles that have GVWR of 10,000 lbs. and under will have the new garage shift Spacer Plate and Orifice Cup Plug. The vehicles with GVWR over 10,000 lbs. have increased clutch capacity requirements which may result in burned clutches if this garage package is installed.

Vehicles with GVWR over 10,000 lbs. cannot be updated with tbis package.

DATE OF CHANGE: (Figure 1) --------------- Beginning November 23, 1987 (Julian Date 327) all THM 400/HYDRA-MATIC 3L80 transmissions with a GVWR of 10,000 lbs. and under were built with a new reverse engagement package.

SERVICE ACTION:

To service a 1987-1988 THM 400/HYDRA-MATIC 3L80 transmission built prior to November 23, 1987 (Julian Date 327) it is necessary to replace the Case Assembly, Spacer Plate, and valve body gaskets listed under "Service Parts Information". (Refer to Figures 2 through 6.)

NOTICE: When installing the Park/Neutral to Reverse engagement shift feel package on a past model transmission built prior to November 23,1987 (Julian Date 327), the original Control Valve Assembly can be used.

SERVICE PARTS INFORMATION:

Model Applications Part No. Part Description (1987 and 1988 only) -------- ---------------- --------------------- 8629970 Package-Case Assembly FDA, FMA, FTA, FZA, LMA, Case Assembly-Complete LTA, LUA, LZA FJA, FPA, Ball FUA, FYA, LBA, LCA, LELA, Plug-Orifice Cup .096" LJA (copper)

8629971 Package-Case Assembly LDA, LFA, LKA, LRA, LSA Case Assembly-Complete LWA, FFA, FNA, FWA, FCA Ball Plug-Orifice Cup .096" (copper) Plug-orifice Cup .089" (blue) use on 4.3L engines only)

8670447 Gasket-Valve Body/Spacer Plate All Models

8670458 Gasket-Case/Spacer All Models *Plate-Valve Body Spacer

* Refer to the Service Parts catalog for correct usage on spacer plates.

Parts are currently available from GMSPO.

SERVICE MANUAL REFERENCE:

Please make note of these changes which are not in your 1988 Service Manual. Refer to the THM 400/475, Unit Repair Section of the Service Manual for proper Case, Control Valve Assembly, Spacer Plate, and Gasket replacement procedures.

SECTION II

TRANSMISSION APPLICATIONS:

1981 Through 1986 THM 400/475 HYDRA-MATIC 3L80/3L80-HD

TRANSMISSION MODELS:

See Attachment

SUBJECT: -------- Service And Parts Information On Case Assemblies For 1981 Through 1986 Model Years

VEHICLE APPLICATIONS:

1981-1986 C, K, P Trucks 1981-1986 G Van

BULLETIN COVERS:

Service Parts and Information for Case replacement procedures for transmissions built from 1981-1986. New Case requires different Spacer Plate and Gaskets.

SERVICE ACTION: (Reference Attachment) --------------- When ordering a service transmission Case for a 1981 through 1986 model year, you will receive a service package that is the same as for a 1987 or 1988 THM 400/475HYDRA-MATIC 3L80/3L80-HD.

When installing this Case package for service in a vehicle built during 1981 through 1986 model year, the original Control Valve Assembly can be reused. The Spacer Plate and Gaskets must be changed. The Checkball and Orifice Cup Plug contained in the service package are not required for 1981 through 1986 model year transmissions and should be discarded. Refer to Service Parts Information.

IMPORTANT: These service packages are to be ordered whenever a transmission Case replacement is necessary. This will not correct a harsh Reverse engagement shift feel on any 1981 through 1986 model year THM 400/475/HYDRA-MATIC 3L80/3L80-HD transmission.

CASE ASM PART # TRANSMISSION MODEL AND YEAR ---------------- --------------------------- 1986 1985 1984 1983 1982 1981 ---- ---- ---- ---- ---- ----- 8629970 FAA FBA 5FA 5FB 4FA 4FB 3FA 3FB 9FA 9FB 8FA 8FB FDA FJA 5FC 5FD 4FC 4FD 3FC 3FD 9FC 9FD 8FF 8FJ FIA FMA 5FJ 5FL 4FE 4FI 3FE 3FI 9FE 9FI 8FL 8FM FPA FQA 5FM 5FP 4FJ 4FL 3FJ 3FM 9FJ 9FL 8FP 8FQ FTA FXA 5FQ 5FT 4FM 4FP 3FP 3FQ 9FM 9FP 8FR 8FT FIA FSA 5FX 5FI 4FQ 4FS 3FS 3FT 9FQ 9FS 8FY FCA LSA 5FS 4FT 4FU 3FU 3FX 9FT 9FX 4FX 4MF 8629971 FKA FNA 5FF 5FR 4FF 4FH 3FF 3FH 9FF 9FH 8FH 8FO FWA FZA 5FV 5RV 4FK 4FN 3FK 3FN 9FK 9FN 8FN 8FW FFA FRA 5VR 5VS 4FR 4FV 3FR 3FV 9FW 9FY FVA FYA 5VV 5FK 4FW 4FY 3FW 3FY 9FZ 9RV LRA 5FN 5FW 4FZ 3FZ 5FZ 8627961 4AN

SPACER PLATE PART NO. -------- 8670448 FAA FBA 5FA 5FB 4FA 4FB 3FA 3FB 9FA 9FB 8FA 8FB FIA FJA 5FC 5FI 4FC 4FE 3FC 3FE 9FC 9FE 8FF 8FH FKA FLA 5FJ 5FK 4FH 4FI 3FE 3FH 9FH 9FI 8FJ 8FL FMA FNA 5FL 5FM 4FJ 4FK 3FI 3FJ 9FJ 9FK 8FM 8FN FQA FTA 5FN 5FQ 4FL 4FM 3FK 3FM 9FL 9FM 8FO 8FQ FWA FZA 5FT 5FW 4FN 4FQ 3FN 3FQ 9FN 9FQ 8FR 8FT FVA FCA 5FZ 5VR 4FT 4FW 3FT 3FW 9FT 9FW 8FW 8FY FYA LRA 5RV 5VV 4FZ 4MF 3FZ 9FZ 9RV LSA 5VS

8670452 FDA FSA 5FD 5FF 4FD 4FF 3FD 3FF 9FD 9FF 8FP FPA FFA 5FR 5FP 4FR 4FP 3FR 3FP 9FS 9FP FXA FVA 5FV 5FS 4FU 4FS 3FU 3FS 9FY 9FA FRA 5FX 5FX 4FX 4FV 3FX 3FV 4AN 3FY 4FY

GASKET-VALVE BODY/SPACER PLATE ------------------------------ PART# ----- 8670447 ALL MODELS

GASKET-CASE/SPACER PLATE ------------------------ PART# ----- 8670458 ALL MODELS

Parts are currently available from GMSPO.

IMPORTANT: When ordering Case Packages 8627961, 8629970 or 8629971, order the appropriate Spacer Plate and Gaskets at the same time.

SERVICE MANUAL REFERENCE:

Refer to the THM 400/475 Unit Repair Section of the Service Manual for the proper replacement procedures. This information is not contained in any 1988 or prior model year Service Manual. Please make note of this information for future use.

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.