Section 00-04: Noise, Vibration and Harshness
1996 F-150, F-250, F-350, Bronco and F-Super Duty Workshop Manual
Neutralize the exhaust system to relieve strain on mounts which may be sufficiently bound up to transmit vibration as if grounded.
Make sure the system is warmed up to normal operating temperature, as thermal expansion could be the cause of a strain problem.
Loosen all hanger attachments and reposition hangers until they hang free and straight. This should include the steady rest rod from the exhaust system to the area of the rear engine (engine mount on some applications).
Loosen all flange joints and, with engine running, shift transmission from neutral to drive and back to neutral (or load engine with clutch) and retighten all hanger clamps and flanges (tighten the manifold-to-exhaust flange joint last). Refer to Section 09-00 for correct installation and torque specifications.
After neutralization, the rubber in the exhaust hangers should show some flexibility when movement is applied to the exhaust system.
Verify adequate clearance to prevent grounding at any point in the system. Road test the vehicle and if moan persists, refer to Pinpoint Test B in the Diagnosis and Testing portion of this section.