Celebrity V6-173 2.8L VIN X 2-bbl (1985)
Technical Service Bulletin # 921307A
Date: 920301
A/T - Harsh Shift Conditions Service Information
Number:
92-130-7A
Section:
7A
Date:
MARCH 1992
Corporate Bulletin No.: 977162R
ASE No.: A2
Subject:
HARSH SHIFT CONDITIONS AND ON-CAR SERVICE INFORMATION FOR HARSH 3-2 DOWNSHIFTS
Model and Year:
1985-90 CELEBRITY WITH 4T60 AUTOMATIC TRANSMISSION
1990-92 LUMINA WITH 4T60 AUTOMATIC TRANSMISSION
THIS BULLETIN CANCELS AND SUPERSEDES DEALER SERVICE BULLETIN NO. 90-140-7A, DATED JANUARY 1990. THE 3-2
CONTROL VALVE SPRING LISTING HAS BEEN UPDATED AND THE 1991-92 MODEL YEARS HAVE BEEN ADDED. ALL COPIES OF
90-140-7A SHOULD BE DISCARDED.
IMPORTANT:
Before performing any service, verify the customer's concern is a 3-2 downshift and not a 2-1 downshift concern. A TECH 1 or other scan tool can be
used as an aid to make this determination. Also, it would be an aid for diagnosis to put the transaxle in manual 3rd, or 2nd before and after the concern to
determine actual gears of the shift complaint.
NOTICE:
DO NOT USE General Motors limited slip differential lubricant additive or equivalent to eliminate undesirable "shift-feel," reduce harsh shifting, or to
minimize torque converter apply/release "shudder." This will prematurely distress the clutches and bands in the transaxle/transmission by elongating
shift-engagement times and increasing slippage between surfaces, even though it might provide better shift-feel for the customer at first. Also, the static
capacity (a measure of load-holding capacity) will be reduced by at least 50 percent (i.e., the transaxle/transmission will only handle one half the
Combined Gross Vehicle Weight as it did before without slipping).
THE BOTTOM LINE:
The customer will be pleased at first, but will be back to the dealership with a distressed transaxle/transmission.
BULLETIN COVERS:
Harsh 3-2 shift conditions and specific service information which applies to the correction of these conditions. Before resorting to the 3-2 Service
Packages available, verify that the harsh condition is not caused by the following:
-
Vacuum Leaks (low vacuum supply to the vacuum modulator) Remember, the available vacuum will be less at higher altitudes. Also, a restricted
exhaust (plugged catalytic converter) can cause a low vacuum. Measure exhaust system pressure as outlined in Section 6F of the Service Manual.
-
Faulty Vacuum Modulator (19) Check for proper modulator function as outlined in Section 7 (Transaxle Unit Repair) of your Service Manual.
Also verify the modulator valve (17) moves freely in its bore and is free of nicks or burrs.
-
Sticking 1-2 Servo Control Valve (373) in Control Valve Assembly (35)
-
Sticking 3-2 Control Valve (340) in Control Valve Assembly (35)
-
Missing or Mislocated Checkballs (2, 4, 12) (refer to Figure 2)
-
Sticking 3-2 Coastdown Valve (218) in Oil Pump Assembly (44)
-
Improper T/V Cable Adjustment (refer to Section 7A of your Service Manual for the proper T/V cable adjustment procedure)
IA. Very Harsh Part Throttle 3-2 Shift At 20-40 MPH
1985 - 1990 A Cars 1990 W CARS
Service Procedure:
