NO GEARS/SLIPPING ALL RANGES STICKING REVERSE BOOST VALVE

Model and Year ALL TRUCKS WITH THM 400

Some 1984 THM 400 transmissions built between February 1, 1984 and March 31, 1984 may experience no gears or slipping in all ranges. Refer to the chart below for model and serial number applications affected.

When servicing any 1984 THM 400 transmission which is listed in the chart below and exhibits the above condition, you may find either the forward clutch snap ring mislocated or out of its seat and some seals blown out of their seat.

If these conditions are found they may be caused by a sticking reverse boost valve in the reverse boost bushing. It is very important to visually inspect the reverse boost bushing which is located in the oil pump assembly for possible mismatching of the inner diameter. Refer to the illustration letters 'A' and 'B' for examples.

If the reverse boost bushing is like letter 'A', the bushing and valve must be replaced. Order service package 8625902 which contains the following.

Service Package 8625902 contains:

1 - Regulator Boost Valve Bushing 1 - Regulator Boost Valve

Model Serial Numbers Model Serial Numbers ----- -------------- ----- ---------------

FA 9745 to 12760 FN 2372 to 2873 FB 8498 to 11466 FP 9960 to 12837 FC 1027 to 1051 FQ 1714 to 1860 FD 7065 to 9425 FR 1069 to 1119 FE 1003 to 1004 FT 1255 to 2050 FF 3610 to 4254 FV 8735 to 12185 FH 1701 to 2057 FW 11270 to 14565 FJ 6335 to 7739 FX 1949 to 2146 FK 1136 to 1401 FY 1608 to 1833 FM 34782 to 47400 FZ 1178 to 1225 MF 43420 to 49554

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.