Bafang BBSHD Disassembly/Nylon Gear Replacement

Diagnosing and Repairing a Bafang BBSHD Motor with a Stuck Axle

Gary Salo from Golden Motor Canada walks you through a thorough repair process on a Bafang BBSHD motor where the axle fails to turn even though the motor hums and the display remains active.

The issue begins when throttle is applied: the motor sounds like it’s trying to run, but the axle does not move and abruptly stops. Initially, the controller was suspected, as it is often the weakest link. However, after testing with a new controller, it was confirmed that the controller is functioning correctly.

The next step involved removing the drive cover, which is held on by six bolts, to inspect the internal components. Inside, the main steel gear was examined; the teeth were intact, and it moved smoothly. The axle and bearing appeared sound but were somewhat lacking in grease, so lubrication was applied. The paper gasket that seals the drive cover usually tears when removed and needs replacement; care was taken during removal to avoid damage. Wiring, including the phase wires and sensor cables, was inspected and found to be in good condition.

To access the motor core housing the rotor and nylon gear, four screws were removed using a 3 mm Allen wrench. The rotor shaft and hall sensor plug were checked and appeared well-greased and undamaged. To rule out rotor failure, the controller was connected directly to the rotor, with all phase wires and hall sensor plugged in. Upon applying throttle, the rotor spun smoothly, confirming the rotor was not the source of the problem.

Attention then turned to the nylon gear inside the motor core. To remove the nylon gear, three M4 screws were carefully threaded into designated holes to push the cover off evenly without damage. Upon removal, the nylon gear was visibly damaged. It is secured by a snap pin, which was carefully removed using snap pin pliers without causing harm to surrounding components. The damaged nylon gear was taken out for replacement.

A brand-new nylon gear was prepared for installation. Both the gear and rotor shaft were generously greased with white lithium grease. The gear was pressed onto the shaft, ensuring the side with deeper indentations faced upward, as per manufacturer specifications. The snap pin was reinstalled to securely hold the nylon gear in place, and the motor core cover was replaced.

Reassembly followed, including fitting a new paper gasket to replace the torn seal and applying grease to the main steel gear for smooth operation. With the battery and display powered on, throttle was applied and the axle rotated freely. Pedal assist was tested through all levels up to nine, working perfectly without issue. An Error 21 appeared indicating the speed sensor was disconnected; however, the motor itself functioned normally. Final steps involved reinstalling rubber grommets and applying silicone sealant to waterproof the assembly.

This repair highlights how a damaged nylon gear can cause the motor axle to seize despite the motor running normally. Replacing the nylon gear restored proper function. Proper lubrication and regular inspection of internal components can help prevent similar failures.