M/T - Updated Gaskets
88chevy14Number: 88-266-7B
Section: 7B
Date: JUNE, 1988
Subject: STYRENE RUBBER COATED FIBER GASKETS FOR
HM117, CH465, SM465 TRANSMISSIONS
Model and Year: 1968-88 TRUCKS WITH HM117, CM/SM465 MANUAL TRANSMISSIONS
(RPO M20/MC8)
TO: ALL CHEVROLET DEALERS
FIGURE 1 - NEW GASKETS:
This bulletin covers service information on vehicles equipped with a HM-117 or CH/SM 465 manual transmission (Figure 1) that may have fluid leaks. These fluid leaks should be serviced with new styrene rubber coated cellulose fiber gaskets, insuring flatness of the case mating surfaces and the addition of sealant to specified parts. The new gaskets are for the (top) cover (6), power take off (PTO) covers (58), main drive gear retainer (53), countershaft front bearing cap (75) and a universal 2WD and 4WD rear bearing retainer gasket (77 and 88).
FIGURE 2 - HM-117 TRANSMISSION IDENTIFICATION INFORMATION CH/SM 465 RPO M20 - MC8:
DATE OF PRODUCTION CHANGE: (Figure 2)
All units built after February 15, 1988 will have the new gaskets described above.
The jack screw holes in the cover were eliminated for the R/V and P Truck applications on February 4, 1988 and the C/K Truck applications on April 15, 1988.
FIGURE 3 - DOWEL PIN LOCATION:
SERVICE ACTION:
Inspect the case (59) mating surfaces for flatness using a metal straight edge and feeler gauge. If a 0.13 mm (0.005 in.) feeler gauge can be put under the straight edge at any point, replace the case.
On models built before July 6, 1987 with a dowel pin hole that goes through the inside of the case, put RTV silicone specified in Service Parts Information around the edge of the dowel pin (7) that is on the cover (2) to prevent leakage (Figure 3).
FIGURE 1 - NEW GASKETS:
For all models, install the new gaskets and put pipe sealant with teflon (TM) or equivalent on all the bolts. Put pipe sealant with teflon (TM) or equivalent on the drain and fill plugs (76), then torque all bolts and plugs to the specifications listed in Figure 1. The countershaft front bearing cap bolt (73) torque specification has been increased to 4 N-m (3 ft.lbs.) to prevent leakage.
SERVICE PARTS INFORMATION:
P/N 8672945 New Service Parts Gasket and Seal Package Contents:
Quantity Part Description
1 Gasket, Rear Bearing Retainer (2WD and 4WD)
1 Gasket, Main Drive Gear Bearing Retainer
1 Gasket, Countershaft Front Bearing Cap
2 Gasket, Power Take Off Cover
1 Gasket, Cover
1 Seal, Main Drive Gear Bearing oil
1 Seal, U-Joint Front Flange Oil
Listed below are sealants referred to in this bulletin:
Quantity Part No. Part Description
1 1052080 Pipe Sealant with Teflon (TM) (50 ml -
1.69 oz)
1 1052917 RTV Silicone GMS Type B (89 ml - 3 oz)
SERVICE MANUAL REFERENCE:
Refer to the unit repair section of the appropriate service manual for the procedures.
Please record this information in any 1988 or earlier model year service manual. 1989 and future service manuals will include these revisions.
SERVICE NOTES:
Refill the transmission with only SAE 80W or SAE 80W-90 gear lubricant. Do not use automatic transmission fluid or engine oil. This may cause foaming out the vent and durability concerns.
IMPORTANT: Some 1988 C/K Trucks equipped with a HM-117 may leak out the vent. To correct this condition, refer to Dealer Service Bulletin 88-44-7B, dated October, 1987, outlining the procedure to add a remote vent system.
On models equipped with the remote vent system, do not use a SAE 80W or SAE 80W-90 gear lubricant that has a hypoid additive (a GL5 rating on the label). This may cause a gear oil smell inside of the vehicle.