Electric Bicycle Mechanical Fault Repair Experience: Diagnosis, and Repair Case Analysis
Mechanical faults are often overlooked, but many e-bike problems are purely mechanical: a chain that rubs the chain guard, a bike that is hard to pedal, or a drum brake that squeals or fails to return. Mechanical faults usually produce clear symptoms: noise, abnormal resistance, and poor operation. They commonly result from looseness, misalignment, wear, or dirt. This guide covers the common ones in two parts: quick-reference tables organized by symptom, followed by eighteen real repair cases, each presented from symptom to repair.
Troubleshooting Guide for Mechanical Faults in Electric Bicycle Frames
1. Unusual Noises
See Table 1 for the symptoms, causes, and troubleshooting methods related to unusual noises in the frame.
Table 1: Symptoms, Causes, and Troubleshooting Methods for Unusual Noises in Electric Bicycles
| Fault Symptom | Cause | Troubleshooting |
| Noise caused by friction or contact between the chain and the chain guard | Chain is too loose | Loosen the rear axle nut, pull the rear wheel backward to adjust the chain to the proper position, then tighten the nut |
| Chain guard is warped or damaged | Realign the chain guard or replace it with a new one | |
| While riding, the chain, chainrings, and cassette make a “clattering” noise | Chain is too tight | Loosen the rear axle nut, move the cassette forward to loosen the chain to the proper position, then tighten the nut |
| The chain, chainring, and cassette are not running in the same plane | Adjust the chainring and cassette so they are in the same plane | |
| Sprocket axial runout | Align the sprocket | |
| Chain pitch elongation | Replace the chain | |
| Noise caused by the crank colliding with the chain guard | Loose bottom bracket bearings | Adjust the bearing clearance |
| Chain guard misaligned | Adjust the chain guard position | |
| Crank feels loose and makes noise while riding | Loose fit between the crank and bottom bracket (i.e., damaged pin) | Tighten or replace the crank pin |
| Noise caused by the tire hitting the fender mount | The rim is misaligned | Adjust the rim and tighten the axle nut |
| The fender bracket screws are loose, causing the fender to shift | First tighten the mudguard bracket screws, then realign the mudguard and tighten the bracket’s mounting screws to the frame | |
| Noise caused by friction between the brake shoes and the wheel rim | Wheel rim misalignment, loose axle nut | Align the rim and tighten the axle nut |
| Brake pad misalignment | Adjust the brake pad position | |
| Noise caused by the front tire rubbing against the front fork leg | Rim misalignment, loose axle nut | Align the rim; tighten the axle nut |
| Rear tire makes a noise when it hits the frame’s horizontal or vertical fork | Rim misalignment; loose rear axle nut | Align the rim and tighten the rear axle nut |
| A rhythmic “tick-tick” sound occurs while riding in electric mode or coasting | Steel balls in the front or rear axle rolling bearings have burst | Disassemble the rolling bearing and replace the steel balls |
| A rhythmic “tick-tick” sound is heard while pedaling | The steel balls in the bottom bracket rolling bearing have fractured (assuming the above issue has been ruled out) | Disassemble the bottom bracket roller bearing, replace the steel balls |
| A strange noise is heard when turning the handlebars | The steel balls in the front fork roller bearings have fractured | Disassemble the roller bearings in this area and replace the steel balls |
Note: When replacing balls in any rolling bearing, replace all balls on the same side—regardless of whether they are intact—to prevent uneven force distribution caused by mixing new and old balls. If the axle retainer is severely worn, damaged, or pitted, replace it at the same time.
2. Difficulty Riding
See Table 2 for symptoms, causes, and troubleshooting methods related to difficulty riding an electric bicycle.
| Symptoms | Causes | Troubleshooting |
| During normal riding, the bike feels heavy, and both electric and pedal operation are difficult, while the speed remains slow | Underinflated tires or slow air loss increase rolling friction between the tires and the ground | Inflate the tires; if the tires are slowly losing air, inspect and repair them before re-inflating and riding |
| The rim is rubbing against the brake pads or other parts, causing friction | Align or adjust the wheel; Adjust the brake pad position | |
| Excessive frictional resistance in the front, rear, and bottom bracket bearings | Loosen the over-tightened axle stops on the front, rear, and bottom brackets appropriately. If the chain is too tight, causing excessive frictional resistance in the bottom bracket and rear axle, adjust the chain tension. If excessive friction resistance on the front, rear, and middle axles is caused by mud, sand, or oil residue, clean the components. If excessive friction resistance is caused by worn rolling bearing parts or burnout due to lack of lubrication, replace the worn parts | |
| During normal riding, the bike feels heavy, and pedaling is difficult, pedaling is strenuous, and the speed is relatively slow | Excessive friction in the drivetrain | Adjust the relevant components of the drivetrain so that the freewheel, sprocket, and chain are all in the same plane |
| Wheels are loose | Eliminate axial runout of the sprocket; check spoke tension; if insufficient, tighten the spokes |
3. Chain Slipping Off While Riding
See Table 3 for the symptoms, causes, and troubleshooting methods for chain slippage on electric bicycles.
Table 3: Symptoms, Causes, and Troubleshooting Methods for Chain Slippage
| Symptom | Cause | Troubleshooting |
| During normal riding, the chain frequently falls off the freewheel or chainring | Chain is too loose | Tighten the chain |
| The chainring, chain, and cassette are not in the same plane | If the rear wheel cannot be moved backward any further and the chain is still too loose, remove the chain, shorten it, and then reinstall and adjust it | |
| The sprocket exhibits axial play (i.e., wobbles side-to-side) | Align the sprocket and rear wheel properly, and correct the frame distortion and the position of the horizontal and vertical fork tubes | |
| The chain pitch has stretched, causing poor engagement with the chainring or cassette | Adjust the sprocket’s axial runout; replace the chain with a new one; recondition the old chain whose pitch has been stretched | |
| Wear on the sprocket or freewheel teeth causes poor meshing with the chain | Replace the sprocket or flywheel |
4. Crank Slippage
See Table 4 for the symptoms, causes, and troubleshooting methods for crank slippage in electric bicycles.
Table 4: Symptoms, Causes, and Troubleshooting Methods for Crank Slippage
| Symptoms | Causes | Troubleshooting Methods |
| While riding, when the crank rotates forward, it suddenly slips forward and drops into a gap, or a noise is heard as the crank rotates | The crank pin is loose in the crank | Tighten the crank pin on the slipping crank |
| Mixed use of metric and imperial crank pins, causing a mismatch | If the crank pin is damaged and inoperable, replace it | |
| The square taper section of the crank and the bottom bracket do not align | Use a wooden mallet to tap the outer end of the crank toward the bottom bracket, then tighten the lock nut |
5. Freewheel Slippage
See Table 5 for the symptoms, causes, and troubleshooting methods for freewheel slippage on electric bicycles.
Table 5: Symptoms, Causes, and Troubleshooting Methods for Freewheel Slippage
| Symptom | Cause | Troubleshooting Method |
| When pedaling, the chain fails to propel the bike forward, or it moves intermittently | Poor engagement between the freewheel pawl and the inner teeth of the freewheel housing | Clean dirt from the freewheel to prevent the pawl from sticking due to grease, allowing it to spring back and function properly. Adjust the pawl spring, ensuring it fits into the spring’s groove; replace the spring. If the spring head is severely worn, replace it with a new one; if the inner teeth of the freewheel housing are severely worn, replace the freewheel housing. |
6. Wobbling Rims
See Table 6 for the symptoms, causes, and troubleshooting methods for wobbling rims on electric bicycles.
Table 6: Symptoms, Causes, and Troubleshooting Methods for Wheel Wobble
| Symptom | Cause | Troubleshooting |
| While riding, the wheel wobbles erratically, veering sometimes to the left and sometimes to the right | Excessive play in the front or rear axle roller bearings | Adjust the play in the rolling bearings |
| The spokes are unevenly tensioned, causing the wheel to wobble and lock in a specific position | Adjust the tension of the spokes | |
| Damaged or mismatched steel balls in the front or rear axle | Replace the steel balls | |
| Damaged components inside the rolling bearing | Replace the damaged parts |
7. Front Wheel Misalignment
See Table 7 for the symptoms, causes, and troubleshooting methods for front wheel misalignment on electric bicycles.
Table 7: Symptoms, Causes, and Troubleshooting Methods for Front Wheel Misalignment
| Symptoms | Causes | Troubleshooting |
| While riding, the handlebars are in the correct position, but the front wheel veers to the left or right | Loose front axle nut | Adjust the play in the front axle ball bearings and tighten the front axle nut |
| Relative movement between the handlebars and the fork caused by an impact or a loose centering bolt | Tighten the centering bolt | |
| Deformed fork steerer tube or fork legs | Straighten the fork steerer tube or fork legs; if the problem persists, replace the fork |
8. Front or Rear Wheel Wobble
See Table 8 for symptoms, causes, and troubleshooting methods for front or rear wheel wobble on electric bicycles.
Table 8: Symptoms, Causes, and Troubleshooting Methods for Front or Rear Wheel Wobble
| Fault Symptoms | Causes | Troubleshooting |
| The front wheel wobbles inside the front fork, or the rear wheel wobbles inside the frame’s horizontal or vertical dropouts | Loose front or rear axle nut | Tighten |
| The rolling bearings on the front or rear axle are installed too loosely | Adjust |
9. Crank Turns on Its Own
See Table 9 for the symptoms, causes, and troubleshooting methods related to the crank turning on its own on electric bicycles.
Table 9: Symptoms, Causes, and Troubleshooting Methods for the Crank Turning on Its Own
| Symptom | Cause | Troubleshooting Method |
| While pushing the cart forward, the crank occasionally rotates forward on its own | Excessive grease on the flywheel causes the flywheel outer shell and core to rotate together | Tilt the cart to the left, pour kerosene into the gap between the flywheel outer shell and the gear rack, and reverse the chain rotation, to clean the dirt inside the flywheel; then disassemble the flywheel and clean the internal dirt |
| The flywheel rolling bearing is too tight | Adjust the flywheel rolling bearing |
10. Caliper Brake Failure
See Table 10 for the symptoms, causes, and troubleshooting methods for caliper brake failure.
Table 10: Symptoms, Causes, and Troubleshooting Methods for Caliper Brake Failure
| Symptoms | Causes | Troubleshooting Methods |
| Failure of Clamp-Type Brake | Brake lining is too far from the wheel rim | Adjust the clearance between the brake lining and the wheel rim |
| Wire rope sleeve is broken or cracked | Replace the wire rope sleeve and clean any mud, sand, or other debris stuck to the wire rope | |
| The wire rope is stuck to the wire rope sleeve | Lubricate the wire rope and wire rope sleeve with oil | |
| The cable tensioning screw has come loose | After adjusting the clearance between the brake lining and the brake ring, tighten the cable tensioning screw | |
| The wire rope has stretched | Loosen the cable tensioning screw, adjust the distance between the brake lining and the rim, then tighten the cable tensioning screw | |
| Brake fork is only engaging on one side | Adjust the set screw so that the brake fork moves freely, and adjust the brake spring so that the spring force is uniform on both sides |
11. Poor Reset of the Caliper Brake
See Table 11 for the symptoms, causes, and troubleshooting methods for poor reset of the caliper brake on electric bicycles.
Table 11: Symptoms, Causes, and Troubleshooting Methods for Poor Reset of the Caliper Brake
| Symptoms | Causes | Troubleshooting |
| The caliper brake caliper fails to reset promptly after braking, or only one side resets while the other remains stationary | Improper installation; mounting screws are too tight; the wire rope has sharp or tight bends | Adjust the mounting screws so the brake fork moves freely; adjust the brake springs to ensure even tension on both sides; replace the wire rope and wire rope sleeve |
12. Tire Cannot Be Inflated
See Table 12 for the symptoms, causes, and troubleshooting methods for electric bicycle tires that won’t inflate.
Table 12: Symptoms, Causes, and Troubleshooting Methods for Tires That Won’t Inflate
| Symptom | Cause | Troubleshooting |
| Tire won’t inflate | The valve core’s air inlet is blocked | Unscrew the inflation nut, remove the valve core, and detach the valve hose. Use a thin wire or the tip of a needle to remove any dirt, sand, or debris |
| The valve hose has melted and is blocking the valve core hole | After removing the valve core using the method described above, clean it with gasoline or a similar solvent, then clear the passage with a thin wire. Once you’ve confirmed it’s unobstructed, replace the rubber tube | |
| Extremely cold weather causes moisture in the valve rubber tube to condense into ice, blocking the air passage | Remove the hose and heat it over a flame to melt the ice, and shake off any water droplets | |
| Pump issues | Inspect or replace the pump |
13. Slow Tire Leaks
See Table 13 for the symptoms, causes, and troubleshooting methods for slow leaks in e-bike tires.
Table 13: Symptoms, Causes, and Troubleshooting Methods for Chronic Tire Leaks
| Symptoms | Causes | Troubleshooting Methods |
| The air in the tire gradually decreases or is completely depleted within 2–3 days | The valve tube is cracked or has become soft due to aging | Unscrew the inflation nut, remove the valve core, and replace the valve tube |
| The inflation nut is not tightened | Tighten the inflation nut | |
| Poor seal where the valve stem and valve washer contact the inner tube | Unscrew the inflation nut and the round nut, remove the valve core from the tire, use a wrench to tighten the nut on the valve gasket, or add an additional rubber washer under the valve gasket. Remove the inner tube, inflate it, and inspect it carefully; if there is a leak, patch it | |
| The inner tube is defective (e.g., pinholes) or the previously patched area is leaking | If a previously patched inner tube is leaking, it must be patched again; however, before re-patching, thoroughly scrape away all traces of the old patch from the affected area |
14. Quick Repair and Troubleshooting Guide for Frame Mechanical Faults
See Table 14 for symptoms, causes, and troubleshooting methods for mechanical faults in electric bicycle frames.
Table 14: Symptoms, Causes, and Troubleshooting Methods for Frame Mechanical Faults
| Fault Symptom | Cause of Fault | Troubleshooting Method |
| Front fork wobbles | Improper clearance in front fork rolling bearings | Loosen the lock nut, adjust the stop screw to the proper position, then retighten the lock nut |
| Saddle tilts horizontally to the left or right | Loose nut at the rear frame junction | After realigning the saddle, tighten the rear joint nut on the frame |
| The front of the saddle tilts up or down | The saddle’s clamping nut is loose | After realigning the saddle, use a wrench to tighten the saddle’s clamping nut |
| The front or rear wheel does not rotate in its normal position; it veers to one side | The front or rear axle nut is loose | Simply tighten them |
| The brake shoes are too far from the rim | The clearance between the brake shoes and the rim is too large | Adjust the clearance |
| Only one side of the brake fork is engaging | The brake fork cannot move freely; spring tension is uneven on both sides | Adjust the set screws and the brake springs |
| The wire rope is not flexible | The wire rope has sharp or tight bends | Replace the wire rope and wire rope sleeve |
| The wire rope is stuck to the wire rope sleeve | Dirt, sand, or other debris on the wire rope; insufficient lubrication in the wire rope sleeve | Remove debris and apply lubricant |
| Wire rope elongation | Improper clearance between the brake lining and the wheel rim | Loosen the tensioning screw, make the adjustment, then tighten the tensioning screw again |
| The brake fork of a caliper brake fails to reset promptly after braking, or only one side resets while the other remains stationary | Improper installation; mounting screws are too tight; the wire rope has sharp or tight bends | Adjust the mounting screws so that the brake fork moves freely. Adjust the brake springs to ensure even tension on both sides. Replace the wire rope and wire rope sleeve |
| Poor reset of the clamp-type brake fork | Improper installation; set screws are too tight | ① Adjust the set screws so that the brake fork moves freely ② Adjust the brake springs so that the tension is even on both sides |
| Caliper brake failure | ① Brake lining is too far from the wheel rim ② Wire rope sleeve is broken or cracked ③ Wire rope is stuck to the wire rope sleeve ④ Tensioning screw is loose ⑤ Wire rope has stretched ⑥ Only one side of the brake fork is engaging | ① Adjust the clearance between the brake lining and the wheel rim ② Replace the wire rope sleeve with a new one ③ Remove any dirt, sand, or other debris stuck to the wire rope ④ After adjusting the clearance between the brake lining and the wheel rim, tighten the wire tensioning screw ⑤ Loosen the cable tension screw and adjust the distance between the brake pad and the rim ⑥ Adjust the set screw so that the brake caliper can move freely, and adjust the brake spring to ensure even tension on both sides |
| While riding, the handlebars are in the correct position, but the front wheel veers to the left or right | ① The front axle nut is loose ② Relative movement has occurred between the handlebars and the fork due to an impact or a loose centering bolt; the fork steerer tube or fork legs are bent | ① Adjust the front axle play and tighten the front axle nut ② Straighten the fork steerer tube or fork legs; if the problem persists, replace the fork |
| The front wheel wobbles in the fork, or the rear wheel wobbles in the frame’s flat or vertical dropouts | ① Loose front or rear axle nut ② The front or rear axle assembly is too loose | ① Tighten ② Adjust |
| The handlebars and fork do not turn as a single unit; when steering, the fork (including the front wheel) does not turn with the handlebars, indicating poor balance | The handlebar center bolt is loose, and the centering nut has not been tightened | ① Use a wrench to tighten the hex nut on the centering bolt ② While tightening, align the front wheel in the fork with the handlebars |
| The handlebars do not turn smoothly while riding; they feel stiff or make noises | The upper and lower bearings, cups, and steel balls are scratched, deformed, or pitted | Remove the fork tube and check the upper and lower races, cups, and steel balls for damage, deformation, or pitting; replace them promptly if found |
| The bottom bracket locks automatically and cannot be turned | The locking nut on a Type A bottom bracket is loose, causing the bottom bracket rolling bearings to seize | Adjust the clearance of the bottom bracket rolling bearings |
| While riding, when the crank rotates forward, it suddenly slips forward and drops a gear, or makes a noise when turning | ① The crank pin is loose in the crank ② Metric and imperial crank pins are used interchangeably, causing the crank pins to not align properly ③ The crank and the bottom bracket’s square taper do not align | ① Tighten the crank pins on the loose crank; if a crank pin is damaged and no longer functions, replace it with a new one ② Replace with the correct crank pins ③ Screw the outer end of the crank toward the bottom bracket, then tighten the locking nut |
| Tire pressure decreases or the tire deflates completely within 2–3 days | ① The valve stem hose is cracked or has become soft due to aging ② The inflation nut is not tightened ③ Poor seal where the valve core and valve gasket contact the inner tube ④ The inner tube is defective (e.g., micro-holes), or there is a leak at a previously patched area | ① Unscrew the inflation nut, remove the valve core, and replace the valve tube ② Tighten the valve cap ③ Remove the valve stem from the tire, then use a wrench to tighten the nut on the valve washer, or add an additional rubber washer beneath the valve washer ④ Remove the inner tube, inflate it, and inspect it carefully; patch any puncture holes |
| During normal riding, the bike feels heavy, pedaling is difficult, and the speed is slow | ① Underinflated or slowly deflating tires increase rolling resistance ② The rim is rubbing against the brake pads or other parts ③ Excessive frictional resistance between the front, rear, and bottom bracket bearings ④ Excessive frictional resistance in the drivetrain ⑤ Wobbly wheels | ① Inflate the tires. If the tire is slowly losing air, repair it ② Align or adjust the wheels; adjust the brake pads to the correct position ③ Loosen any front, rear, or middle axle locknuts that are too tight; If the chain is too tight, causing excessive frictional resistance on the middle and rear axles, adjust the chain tension ④ If mud, sand, or oil residue causes excessive frictional resistance on the front, rear, and middle axles, clean them. If frictional resistance is too high due to wear on rolling bearing components or seizing caused by lack of lubrication, replace the worn parts, and properly adjust the relevant components of the drivetrain. Ensure that the wheel, sprocket, and chain are all in the same plane. Eliminate axial runout of the sprocket ⑤ Check the spoke tension; if insufficient, tighten the spokes |
Case Studies on Mechanical Faults and Repairs of Electric Bicycles
Case 01: Crank Slipping on the Bottom Bracket While Riding an Electric Bicycle
Fault Symptoms:
While riding the electric bicycle, when the crank rotates to a certain position, it suddenly slips forward a short distance and emits a “clang” sound.
Troubleshooting:
Possible causes and repairs:
a. The crank pin lock nut is loose; tighten it.
b. The clearance between the crank pin, crank arm, and bottom bracket is too large; replace with a properly sized crank pin.
c. The square taper sections of the crank and bottom bracket are misaligned. Realign them, tap the crank pin firmly toward the bottom bracket with a hammer, and then tighten the lock nut.
d. The crank pin is loose in the crank; tighten the nut.
Case 02: Electric Bicycle Freewheel Slippage
Fault Symptoms:
While riding by pedaling, the pedals rotate but the chain fails to drive the rear wheel.
Troubleshooting:
The freewheel pawl is not engaging the internal teeth of the outer ring. Possible causes and repairs:
a. The pawl is severely worn and should be replaced.
b. The pawl spring has lost its tension and should be replaced.
c. There is excessive dirt inside the freewheel, causing the pawl to stick and preventing contact with the inner teeth of the outer ring; clean with kerosene or gasoline.
d. The inner teeth of the freewheel outer ring are severely worn and should be replaced.
The freewheel was removed and disassembled, and all components were cleaned. Inspection revealed severe wear on the ratchet pawl and the inner teeth of the outer ring. After replacing the worn parts with new ones and reassembling the unit, the fault was resolved.
Case 03: Poor Braking Performance of an Electric Bicycle Drum Brake
Fault Symptoms:
When applying the brakes while riding a Qianjiang electric bicycle, the bike continued to coast for more than 10 meters before coming to a stop; braking performance was extremely poor.
Troubleshooting:
First, verify that the free play of the brake cable is within the range of 10–20 mm and that the steel cable inside the outer sheath moves freely. This suggests a brake malfunction. Common brake issues include a warped brake drum, brake shoes worn beyond the limit, an insufficient contact area between the friction pads and the drum, or foreign substances such as oil, dust, or other contaminants on the surface that reduce the coefficient of friction, as well as detached friction pads.
Upon disassembling the brake, it was found that the contact area between the friction pads and the brake drum was too small; the friction pads should be resurfaced. The dressing procedure is as follows: Apply a thin layer of red lead powder or other pigment to the friction surface of the brake drum. Mount the brake and wheel hub on the same axle. Press down on the brake arm by hand to ensure the brake shoes contact the brake drum while still allowing relative rotation. After one full rotation, remove the brake and determine the contact area based on the color pattern on the friction pads. If the contact area is less than 70%, use a file to grind the friction lining, checking as you go. Repeat this process several times until the contact area increases to over 70%, then reinstall the brake. When grinding the brake friction lining, be careful not to exceed the grinding limit; otherwise, the friction lining will be rendered unusable. The problem was resolved after grinding the friction lining on this vehicle.
Case 04: Poor Braking Performance in an Electric Bicycle Drum Brake
Fault Symptoms:
A Xinri electric bicycle has been in long-term use, and now exhibits poor braking performance.
Troubleshooting:
Upon inspection, the free play of the brake cable was normal (i.e., 10–20 mm), the brake cable moves freely, and the contact area between the friction lining and the brake drum is over 70%. The brake shoes or camshaft components need to be replaced. Since no replacement parts were available, a strip of thin sheet metal (0.05 mm) was cut to the same width as the camshaft and wrapped around the outside of the brake camshaft (wrapping it several times as needed) to increase the cam’s thickness, thereby reducing the brake clearance and ensuring proper braking performance. This method is best suited for emergency situations; after the emergency has passed, it is recommended to replace the parts to ensure safety.
Case 05: Poor Braking Performance in Drum Brakes Due to Oil Contamination
Fault Symptoms:
West Lake electric bicycles use drum brakes. Due to long-term wear and tear, the brake lining surface becomes smooth. If users allow lubricating oil to seep into the brake assembly, it can lead to poor braking performance, compromising riding safety, and causing the brake lining to turn black.
Troubleshooting:
Apply a layer of rosin powder to the electric bicycle’s brake lining, which will easily resolve the issue. This is because rosin powder has a very high coefficient of friction and is highly adhesive, allowing it to adhere well to the surface of the brake shoes. After repairing the bike using this method, brake slippage has never occurred, and the service life of the brake linings has also been extended.
Case 06: Electric Bicycle Brake Failure
Fault Symptoms:
While riding an Inglai electric bicycle, the braking distance increased.
Troubleshooting:
Prolonged use of an electric bicycle’s rear brake causes wear on its moving parts. Severe wear can impair braking performance or even lead to brake failure. Upon inspection, it was found that the brake camshaft on this bicycle was worn, resulting in insufficient opening of the brake shoes. During repair, provided that the rivet heads remain concealed and the friction pads are undamaged, the opening of the brake shoes can be increased by thickening the camshaft —a method that is both economical and practical. The procedure is as follows:
Find a thin sheet of iron, 0.5 mm thick, and use scissors to cut it into a strip the same width as the camshaft. The length depends on the degree of friction pad wear; generally, it should be long enough to wrap around the camshaft twice. After wrapping it securely, reassemble the brake and install it on the bike. Adjust the brake free play, and it is ready for use.
Case 07: Brake Drag in an Electric Bicycle
Fault Symptoms:
After releasing the brakes while riding the electric bicycle, the bike feels like it loses power and cannot reach its top speed.
Troubleshooting:
The symptoms indicate brake drag.
The causes of brake drag include the following:
a. The brake shoe return spring has weakened or become unhooked.
b. The movement of the wires in the brake control cable is restricted.
c. The free play of the brake lever is too small.
Upon inspection, if the free play of the brake lever is normal and the wires in the brake cable move freely within the outer sheath, this indicates a brake malfunction. Disassembly of the brake revealed that the hook on the brake shoe return spring was broken; after replacing the spring, the fault disappeared.
Case 08: Noise from Drum Brakes During Braking
Fault Symptoms:
Throughout the entire braking process, the brake drum emits a continuous “hissing” or shrill “squeaking” sound, accompanied by a reduction in braking effectiveness.
Troubleshooting:
The primary cause is that the friction linings have worn too thin, exposing the rivets, which then scrape against the brake drum surface, resulting in severe grooves on the drum wall. This is caused by poor cable lubrication, uneven wear on the friction lining contact area, or severe flexural deformation of the friction linings.
Inspection revealed excessive wear on the friction pads and grooving on the brake drum. After machining the drum to a flat surface and replacing the friction pads, the fault was resolved upon reassembly.
Case 09: Sudden Brake Failure in an Electric Bicycle After Riding Through Water
Fault Symptoms:
An electric bicycle that had been ridden through water suddenly experienced brake failure.
Troubleshooting:
An electric bicycle with good braking performance suddenly experienced brake failure immediately after riding through water. Specifically, while riding, squeezing the left and right brake levers did not cause the electric bicycle to slow down or stop. The brake shoe linings are wet and slipping. In this situation, do not rush to inspect other components or adjust the brake clearance. Instead, apply intermittent and repeated braking while the vehicle is in motion. The heat generated by the friction between the brake shoes and the brake drum during braking will cause the moisture to evaporate. This will gradually restore the vehicle’s proper braking performance.
Case 10: Left Brake Lever Is Very Stiff on an Electric Bicycle
Fault Symptoms:
On a “Urban Sunshine” electric bicycle, applying the left brake lever feels very stiff. After releasing the left brake lever, the brake shoe fails to return to its original position and remains in a semi-braked state.
Troubleshooting:
During inspection, disconnect the front brake lever from the front brake control cable. Manually operate the brake lever to check its movement. If the front brake lever rotates freely but it still feels very stiff when squeezing the left brake lever, this indicates that the front brake control cable is not moving smoothly within its outer sheath. Upon removing the front brake control cable, it was found to be severely corroded due to a lack of lubrication. A new front brake control cable of the same specification was installed. During a road test, squeezing the left brake lever resulted in smooth braking, and the lever returned to its original position properly upon release, resolving the issue.
Case 11: Electric Bicycle Brakes Not Responding Properly
Fault Symptoms:
While riding the electric bicycle, when the right brake lever is squeezed, the bicycle decelerates slowly and braking performance is poor.
Troubleshooting:
First, squeeze the right brake lever and check the brake components. Since there was no significant wear, the issue was likely due to insufficient contact area between the brake shoe lining and the brake drum or a warped brake drum. After removing the rear wheel and inspecting the brake shoes, it was found that the inner wall of the rear brake drum had grooves and was slightly out of round. The rear brake drum was replaced, the bike was reassembled and tested. When the right brake lever was squeezed, the brakes engaged smoothly, and the problem was resolved.
Case 12: Excessive Rolling Resistance After Braking on an Electric Bicycle
Fault Symptoms:
On a Ruili electric bicycle, after braking, releasing the right brake lever results in sluggish rear wheel rotation, excessive rolling resistance, lack of acceleration, and significant difficulty pushing the bike forward.
Troubleshooting:
Prop up the electric bicycle on its stand, squeeze the right brake lever to apply the brakes, then release it. Gently turn the rear wheel by hand; if it is difficult to turn, this indicates that the rear brake shoes are not returning to their original position promptly and are still in contact with the inner wall of the rear brake drum, thereby obstructing the rotation of the rear wheel. Remove the rear wheel, take off the rear brake drum cover, and remove the rear brake shoes for inspection. It was found that both the rear brake shoes and the return spring were in good condition. When manually operating the brake lever, it was found to be stiff; this indicates that the brake cam is not rotating smoothly, preventing the rear brake shoe from returning to its original position promptly. The rear brake cam was removed, revealing severe rust. Foreign matter was cleared from the mounting holes on the brake cam and the brake drum cover. The rust on the moving parts of the brake cam was thoroughly removed with fine sandpaper and the surface was polished. The brake cam and its mounting holes were then cleaned with kerosene and allowed to air dry. A small amount of grease was applied to the moving parts of the brake cam before reassembly, and the brake cam rotated smoothly. During a road test, the right brake lever operated smoothly, the brake shoes retracted properly, and the brake cam rotated smoothly; the fault was resolved.
Case 13: High-Pitched Noise When Applying the Rear Brake
Fault Symptoms:
The rear brake on a “Urban Wanderer” electric bicycle emits a high-pitched “squeaking,” which is particularly noticeable when riding in the rain or after washing the bike.
Troubleshooting:
This is most likely caused by the brake shoe lining and the inner surface of the brake drum being too smooth. Remove the rear wheel and take off the rear brake drum cover, remove the rear brake shoes, and use a file or saw blade to roughen the surface of the brake shoe pads. Wipe away any abrasive particles from the pads with a cloth, then sand the inner surface of the rear brake drum with sandpaper. After reassembly, conduct a road test: when the right brake lever is squeezed, the rear brake responds sensitively and effectively, and the high-pitched “squeaking” sound disappears, resolving the issue.
Case 14: Electric Bicycle Brake Light Does Not Illuminate
Fault Symptoms:
When the power switch is turned on or the left or right brake levers are squeezed, the brake light does not illuminate.
Troubleshooting:
Turn on the power switch, and if the horn and turn signals work normally, this indicates that the voltage on the signal and lighting system bus is normal. This indicates that the brake light circuit is faulty. Remove the taillight cover and inspect the bulb; it was not burned out and showed no signs of poor contact. Short-circuiting the brake switches at the left and right brake levers did not resolve the issue. While inspecting the vehicle’s wiring, a loose connector on the brake light bus was discovered. After reseating it, squeezing the left and right brake levers caused the brake lights to function normally.
Case 15: Electric Bicycle Brake Lights Remain Constantly Lit During Braking
Fault Symptoms:
When the power switch is turned on, the brake lights remain constantly lit during braking.
Troubleshooting:
Brake lights must work properly; otherwise, they can cause accidents. The brake lights stay on because the brake switch has failed or the contact rod is misaligned. To resolve this, first check whether the brake switch is functioning properly. Manually press the switch button and observe whether the brake light turns on and off as you press it. If it does not, this indicates a malfunction in the brake switch. Replace the brake switch to resolve the issue.
Case 16: Electric Bicycle Handlebars Occasionally Feel “Wobbly” While Riding
Fault Symptoms:
The “Urban Lover” electric bicycle occasionally experiences difficulty controlling the handlebars, which feel “wobbly”.
Troubleshooting:
This issue is caused by a fault in the steering mechanism. Prop up the main stand to lift the front wheel, then hold the lower part of the front fork with both hands to check that the clearance between the steering column ball bearings and their seats is appropriate. Next, disassemble the steering mechanism and clean the steering column, steel balls, and ball seat rings with kerosene and inspect them; several damaged steel balls were found. After replacing all steel balls and reassembling the unit, a road test was conducted. Steering was smooth and responsive during operation, and the fault was resolved.
Case 17: Steering Suddenly Becomes Unresponsive While Riding
Fault Symptoms:
While riding, the Green Beauty electric bicycle suddenly experienced heavy and unresponsive steering.
Troubleshooting:
The electric bicycle was raised on its main stand, suspending the front wheel off the ground. When the handlebars were turned, steering was smooth. Upon inspecting the front wheel, it was found that the tire pressure was insufficient, causing excessive contact between the tire and the road surface, which resulted in heavy and unresponsive steering. After patching the tire and inflating it to the specified pressure, a road test was conducted. Steering was smooth during the test, and the fault was resolved.
Case 18: Unstable Handlebars on an Electric Bicycle
Fault Symptoms:
While riding a “Urban Wanderer” electric bicycle, the handlebars wobble from side to side, making it difficult to control.
Troubleshooting:
The electric bicycle was raised on its main stand. First, the front tire pressure was checked and found to be normal. When the front wheel was manually moved left and right, it exhibited noticeable wobble. Since the front wheel axle nut showed no signs of looseness, it was determined that the issue was caused by a damaged front wheel hub bearing. After removing the front wheel, it was found that the front wheel hub bearing was damaged, causing the front wheel to wobble left and right while riding, which in turn caused the handlebars to wobble left and right, making the bike difficult to control. The front wheel hub bearing was replaced. After reassembly and a test ride, the handlebars steered smoothly and freely, and the problem was resolved.