A/T - Harsh 3-2 Downshifts: Overview

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Bulletin:
92-74T60-8

Date:
Mar. '92

Ref. No.:
92-175-74T60

Corp. Ref. No.:
977162R


SUBJECT:
HARSH SHIFT CONDITIONS AND ON CAR SERVICE INFORMATION FOR HARSH 3-2 DOWNSHIFTS WITH 4T60 TRANSAXLE

MODELS AFFECTED:
1985-92 CENTURY
1988-92 REGAL
1985-90 ELECTRA/PARK AVENUE
1986-91 LESABRE
1986-90 RIVIERA
1988-90 REATTA


THIS BULLETIN CANCELS AND REPLACES BULLETIN 90-7440-7.

THIS BULLETIN UPDATES THE 3-2 CONTROL VALVE SPRING LISTING AND ADDS THE 1991 AND 1992 MODEL YEARS.


IMPORTANT:
Before performing any service, verify that the customer's concern is a 3-2 downshift and not a 2-1 downshift concern A TECH I 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)