Tech Tip: Pilot Bearing/Bushing Diagnosis

Tech Tip: Pilot Bearing/Bushing Diagnosis

Most rear-wheel drive, and some front-wheel drive, vehicles with manual transmissions use a pilot bearing/bushing. The pilot bearing/bushing supports and centers the transmission input shaft and clutch disc. When the clutch is disengaged, the pilot bearing/bushing allows the flywheel to maintain engine rpm, while the input shaft is slowing down and stopping.

Most rear-wheel drive, and some front-wheel drive, vehicles with manual transmissions use a pilot bearing/bushing. The pilot bearing/bushing supports and centers the transmission input shaft and clutch disc. When the clutch is disengaged, the pilot bearing/bushing allows the flywheel to maintain engine rpm, while the input shaft is slowing down and stopping.

Types of pilot bearing/bushing include conventional ball bearings, needle bearings and sintered bronze bushings.

When a pilot bearing/bushing fails, a driver may exhibit: no release; the transmission may pop out of gear; noise; vibration; and, if not fixed, catastrophic failure of the transmission.

Early signs of the pilot failing may be noise whenever the clutch is disengaged. The driver may also notice that the transmission is difficult to shift between gears or hard to put into reverse or first gear when stopped.

When the pilot is failing, or has failed, the input shaft will be allowed to walk around causing it to go off center. When this happens, the transmission input shaft will begin moving around inside the transmission causing the gears and synchronizers to be off center resulting in the transmission popping out of gear.

figure 1If the vehicle has a high output engine, the misalignment will cause the input shaft gear to not mesh with the counter shaft gear properly and ultimately will cause the gears to fail.  (see figures 1 and 2).

When a clutch is replaced the pilot bearing/bushing should always be replaced as part of the service.

Tech Tip courtesy of Schaeffler Group USA, Inc.

Figure 2

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