A/T - Harsh 3-2 Downshifts, Diagnosis & Repair: Overview

9232OLDS05

NUMBER: 92-T-69

CORP.REF.NO: 977162R

DATE: April 1992

SECTION: 7, 4T60


SUBJECT
HARSH SHIFT CONDITIONS AND ON

CAR SERVICE INFORMATION FOR HARSH 3-2 DOWNSHIFTS

MODELS/YEARS
1985-92 VEHICLES EQUIPPED WITH

HYDRA-MATIC 4T60 TRANSAXLES (RPO-ME9)


This bulletin covers harsh 3-2 shift conditions and specific service information which applies to the correction of these conditions. This bulletin also cancels and replaces Dealer Technical Bulletin 90. T-55, which may 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 customer may be pleased at first, but will be back to the dealership with a distressed transaxle/transmission.

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 1)
^ Sticking 3-2 Coast down Valve (218) in Oil Pump Assenibly (44)
^ Improper T/V Cable Adjustment (refer to Section 7A of your Service Manual for the proper T/V cable adjustment procedure)

IMPORTANT:
Service replacement Transaxle Assemblies (SRTA) are built with original calibrations and may need to be updated wkh a service 3-2 control valve spring per customer requirements.

Refer to the HYDRA-MATIC 4T60 (ME 9) Automatic Transaxle Unit Repair Table of Contents for appropriate service information.