Bronco II 4WD V6-171 2.8L (1985)
Bumper: Customer Interest
Vehicle - Noise/Moan/Drone/Vibration
Article No. 85-2-15
NOISE - NVH - MOAN/DRONE/ VIBRATION
LIGHT TRUCKS 1984 BRONCO II
Some vehicles may experience an audible moan in the 1800-2200 RPM range at highway speed. The following diagnostic procedure provides a method
to diagnose and resolve this condition.
1.
Determine if the concern is related to vehicle speed (mph) or engine speed (rpm). This requires using a tachometer to find the rpm at which the
condition occurs.
NOTE:
To determine if a moan is related to vehicle speed or engine speed, test drive the vehicle in the same transfer case gear, transmission gear,
and hub-lock setting as the customer. Determine the vehicle speed (mph) and engine speed (rpm) of the concern. Check the concern
engine speed and, if possible, the concern vehicle speed in a different transmission gear.
If the moan occurs at the same vehicle speed (mph), then it is a driveline vibration. If the moan occurs at the same engine speed (rpm), it is an
engine induced vibration.
2.
Inspect for and service body to frame ground-out
-
both engine rpm and road speed related.
A ground-out may occur between the rear bumper brackets and vehicle floor pan. If a ground-out is found, provide clearance by readjusting the
bumper bracket.
3.
If the concern is related to engine rpm, neutralize the exhaust system.
a.
Loosen the exhaust system from the manifold.
b.
Loosen the attaching nuts above and below the front engine mounts.
c.
Loosen the transmission support mount from the crossmember.
d.
Start and rev. engine to neutralize engine position on the mounts.
e.
Re-tighten mounts.
f.
Loosen the engine flanges on both sides of the exhaust catalytic converter.
g.
Replace exhaust gaskets and re-tighten, first rear of the catalyst, then forward of the catalyst.
h.
Tighten exhaust system to the manifolds, being careful to place only light pre-load on the forward exhaust hangers. (Slight upward pressure
on the exhaust pipe at the forward hangers should lift the exhaust system off the hangers).
i.
If the moan persists, check the part number of the exhaust insulators. If Part Number E3TA- 5A262-BA, replace with improved insulator Part
Number E4TZ-5A262-B.
4.
If the concern is related to road speed, inspect the driveshaft for tight/binding universal joints.
a.
Shift transfer case to neutral.
b.
Disassemble driveshaft from rear axle.
c.
Work rear U-joint by hand looking for binding/stiffness.
d.
Hold driveshaft in approximate vehicle position and rotate shaft looking for binding/ stiffness in front joint.
e.
If stiffness is found in front joint, disassemble U-joint from transference yoke. Inspect yoke for indication of unacceptable U-joint fit.
f.
Service U-joint and yoke as found necessary.
If these actions do not eliminate the moan completely, do the following:
a.
Complete diagnosis and actions described in Sections 18-01-8 and 18-01-12 of the 1984 Light Truck Shop Manual relating to tip-in moan
and engine accessory vibration respectively. When investigating accessories be aware that removal of the accessory belt may not eliminate the
accessory as a noise source. The accessory must also be loosened from its mounting brackets to eliminate accessory moans being induced by
engine vibrations.
b.
If the concern is related to vehicle speed (mph), follow the diagnostic procedures in sections 18-02-9 and 18-02-11 of the 1984 Light Truck
Shop Manual relative to driveline vibration and driveline angle respectively. If concern persists, replace the rear driveshaft per approved
Shop Manual procedure and test drive. If concern is still present, replace the rear axle ring and pinion gear.
PART NUMBER
PART NAME
CLASS
E4TZ-5A262-B
Insulator, exhaust
C
OTHER APPLICABLE ARTICLES: None
WARRANTY STATUS: Reimbursable within the provisions of the Warranty and Policy Manual.
OPERATION: SP5262A84
TIMES:
