A/T - Park/Neutral to Reverse Engagement Shift Feel
88chevy09Number: 88-189-7A
Section: 7A
Date: APRIL, 1988
Subject: PARK/NEUTRAL TO REVERSE
ENGAGEMENT SHIFT FEEL
Model and Year: 1987/88 C, K, G, R, V
(GVWR OF 10,000 LBS, AND UNDER) WITH THM 400/475
TO: ALL CHEVROLET DEALERS
This bulletin covers service and parts information concerning park or neutral to reverse engagement shift feel on vehicles with a Gross Vehicle Weight Rating (GVWR) of 10,000 lbs. and under. Changes included are: control valve assembly, valve body gaskets, valve body spacer plate, case assembly with an additional check ball and orificed cup plug.
NOTICE:
The new case assembly, control valve assembly, gaskets, and check ball will be included on all THM 400/475 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.
IT IS NOT RECOMMENDED THAT VEHICLES WITH GVWR OVER 10,000 LBS. BE UPDATED WITH THIS PACKAGE.
FIGURE 1 - THM 400 TRANSMISSION IDENTIFICATION INFORMATION:
Beginning November 23, 1987 (Julian Date 327, Figure 1), all THM 400 transmissions with a GVWR of 10,000 lbs. and under were built with a new reverse engagement package.
FIGURE 2 - CASE - VALVE BODY PASSAGES:
FIGURE 3 - PLATE - VALVE BODY SPACER (NON-GARAGE):
FIGURE 4 - PLATE - VALVE BODY SPACER (GARAGE SHIFT):
FIGURE 5 - VALVE BODY OIL PASSAGES:
FIGURE 6 - GASKET - SPACER PLATE TO CASE:
FIGURE 7 - GASKET - SPACER PLATE TO VALVE BODY:
To service a 1987/88 THM 400 transmission built prior to the above date, it is necessary to replace the case assembly, spacer plate, and valve body gaskets listed under "Service Parts Information". The original control valve assembly can be used. Refer to Figures 2 through 7.
SERVICE PARTS INFORMATION:
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 service manual for proper case, control valve assembly, spacer plate, and gasket replacement procedures.