Popping Noise from Cowl Area - Hood Hinge TSB
Hood Hinge: Customer Interest
BodY & Frame - Popping Noise From the Cowl Area
NUMBER:
91-T-167
CORP.REF.NO: 162001R
DATE:
August 1991
SECTION:
2B
SUBJECT:
COWL "POP"/TAPPING NOISE, TRIM HOOD FLANGE, RELIEVE FENDER STRESS, LOOSEN AND SHIM FRONT BODY MOUNTS
MODELS/YEARS:
1991 BRAVADA
Some 1991 Bravadas may exhibit a "popping" noise from the cowl area (at the base of the "A" pillar in front of the speaker grills). The sound may
emanate from either side of the vehicle. The exact cause of this condition is currently unknown.
Cowl "pop" is defined as a tapping noise at the lower corner of the windshield or base of the "A" pillar that usually, but not always, occurs when the
vehicle is cold (below 45 degrees F). The sound is similar to the noise made when tapping a pencil point on the windshield.
Some success has been achieved in correcting this condition by trimming areas of hood flange that may contact the cowl vent panel, by relieving any
stress that may be created by the front fender mounting sequence, and by loosening the # 1 body mount and/or shimming one or both front body mounts.
SERVICE PROCEDURE:
Note:
Typically this condition occurs only when the vehicle sheet metal is at a temperature below 45 degrees F. The condition may temporarily
disappear if vehicle evaluation is performed after a vehicle has been in a warm environment.
Removal of hood flange material:
Some 1991 Bravadas experiencing a cowl "pop" tapping noise may be corrected by trimming the back edge of the hood flange. On a small number
of vehicles, excess material on the rear edge of the hood flange contacts the front of the cowl vent panel causing a tapping noise when the vehicle
goes over a bump.
1.
Visually inspect for witness marks in the painted area of the cowl vent panel to determine if the hood flange contacts any cowl panel surfaces.
2.
If witness marks are not present, it is not necessary to perform Steps 3 and 4. Continue to "Relieving Fender Mounting Stress" Section. If witness
marks are present, trim off approximately 1/8" of the hood flange only in the areas contacting the cowl vent panel using Jilson Tool 1451 SS or
equivalent.
3.
Refinish the bare metal on the trimmed areas and on matching cowl vent panel areas to prevent corrosion.
Relieving Fender Mounting Stress:
Some success has been achieved in correcting the cowl "pop" tapping condition by relieving the stress caused by the front fender mounting
sequence.
1.
Remove windshield wiper arms using Kent-Moore Tool J-8966 Remover and installer, or equivalent.
2.
Remove cowl vent panel assembly.
3.
Loosen the four rear fender mounting bolts to zero torque. (One of the upper fender mounting bolts is located underneath the hood hinge seal.)
4.
Retorque the two lower fender bolts to 20-34 N-m (15-25 Lbs Ft).
5.
The upper hinge mounting bolt should be left at zero torque. Apply Loctite 242 thread locking compound (GM P/N 12345382), or equivalent, to
hold in place. Retorque the remaining upper fender bolt to 20-34 N-m (15-25 Lbs Ft).
6.
Reinstall cowl vent panel assembly and windshield wiper arms.
Loosen and Shim # 1 Body Mount:
1.
Loosen the # 1 body mount to zero torque.
2.
Raise the body off the mount to obtain clearance between the floor and the top of the body mount.
3.
Cut a 4" x 4" square of 1/32 inch thick teflon or nylon (obtain locally) and drill a 5/8" hole through the center. Insert this between the floor pan and
the body mount and lower the body.
Note:
An alternative material is three washer pump shields, P/N 22063244. If three washer pump shields are used, cut three shields (sheets) to size and
locate a 5/8" hole in the center of each shield. Place the three shields between the floor pan and mount, then lower the body on the mount.
