Grand Prix V6-191 3.1L (1989)
Shift Modulator: Customer Interest
A/T - 3-2 Tip-in Flare at 21-24 MPH or Reverse Shudder
Bulletin Number:
89-7-32
Reference Number:
937104
Publish Date:
8/89
Subject:
REVERSE SHUDDER OR 3-2 TIP-IN FLARE AT 21-24 MPH (NEW MODULATOR PIPE)
Models
Affected:
1989 GRAND PRIX MODELS WITH 3.1, 4T60 TRANSMISSION
Condition:
Some 1989 Pontiac Grand Prix vehicles equipped with 3.1L engine and 4 speed automatic transmission may exhibit one or both of the following reverse
shudder conditions:
A.
"Apply" Shudder - When the driver accelerates from a standstill (with transaxle in reverse) the vehicle shudders.
B.
"Lift-Foot" Shudder - When the driver accelerates at light to medium throttle (with transaxle in reverse) then quickly lifts their foot off the throttle the vehicle shudders.
Some of these vehicles may also exhibit a 3-2 tip-in flare condition at 21-24 mph.
Service Procedure:
(Figures 1 and 2)
To repair either of the reverse shudder conditions install a new vacuum modulator pipe assembly which incorporates an in-line .031" brass orifice.
In the unlikely event that the new modulator pipe doesn't eliminate the reverse shudder, an updated calibration package may be installed on any OCJH,
OCHH, OYLH, or OYKH model transaxle built before (Julian date 086) March 27, 1989. All units built after Julian date 086 were built with the updated
calibration. The updated calibration package cannot be used on any other models.
If the new modulator pipe and updated calibration package doesn't eliminate the shudder then reference the 440-T4 Transaxle Diagnosis section in the
Grand Prix Service Manual for other potential causes.
Figure 1 - HYDRA-MATIC 4T60 Transaxle Identification Information
