The front and rear wheels of motorcycles are equipped with independent braking systems. The front wheel brake system is controlled by hand, and the rear wheel brake system is controlled by foot.
The front wheel brake system consists of a front brake operating mechanism and a front brake. The front brake control mechanism adopts brake cable; Front brakes include drum brakes and disc brakes, as shown in Figure 7-37.
Figure 7-37 Brake
The front braking system generally adopts mechanical braking device, but for some large motorcycles with disc brakes for front wheel braking, in order to increase braking strength, hydraulic brakes are used, as shown in Figure 7-38. It is mainly composed of brake handle, brake storage cylinder, brake master cylinder, brake oil pipe, brake caliper and brake disc.
Figure 7-38 Front Disc Hydraulic Brake System
(2) Requirements for front wheel brakes
① Requirements of front wheel drum brake. In addition to the wear resistance of the brake cam and the brake shoe lining, it is also required that the outer circle of the brake lining should be in a complete circle when the brake cam is opened, so as to have a good contact surface with the front hub. In addition, the brake shoe linings must not be contaminated by engine oil.
② Requirements for front wheel disc brakes. The seal of hydraulic disc brake is made of natural rubber. In order not to deteriorate it, only brake fluid is allowed when cleaning or using, and gasoline, kerosene, engine oil and grease are prohibited.
There should be proper clearance between the piston and caliper of the main pump and the inner diameter of the cylinder wall to guide the good sealing of the sealing ring. When the gap becomes larger after wear, it should be replaced in time.
Brake pads are easy to wear, and the friction materials on them should be replaced in time to avoid damaging the brake disc.
The brake disc shall be kept flat, free from deflection and brake fluid pollution.
The tubing joint should be well sealed, and the pipeline joint is not allowed to leak. Copper gaskets are generally used for sealing, and should be replaced in time after being damaged.
(3) Remove the front brake handle.
The disassembly of the front brake handle is shown in Figure 7-39. Unscrew the front brake handle fixing nuts and bolts, and remove the front brake handle and bushing.
Figure 7-39 exploded view of front brake handle
(4) Disassembly of front drum brake
① Lift the front wheel off the ground, and remove the odometer flexible shaft and front brake cable.
② If the front shock absorber is equipped with a front axle bracket, first unscrew the bracket nut and remove the front axle bracket.
③ If the front shock absorber is equipped with side shaft fastening bolts, please unscrew the fastening bolts first.
④ Remove the cotter pin on the front axle, unscrew the front axle nut and pull out the front axle, taking care not to damage the front axle thread. Remove the front wheel together with the brake drum cover.
⑤ Remove the washers and shaft sleeves on both sides, level the front wheel, pry out the oil seal with tools, and be careful not to damage the cutting edge of the oil seal.
⑥ Remove the front hub bearing with a bearing puller, taking care not to damage the inner surface of the center hole of the front hub and the mating surface between the bearings.
⑦ Disassembly of the brake drum cover: The disassembly of the brake drum cover is shown in Figure 7-40. Remove the brake shoe assembly from the brake drum cover, unscrew the bolt, remove the brake rocker arm (remember the relative installation position of the brake rocker arm and the brake cam so as to restore the original position during assembly), then remove the brake rocker arm return spring, brake shoe wear indicator pin, gasket and brake cam, remove the oil seal, and take out the odometer driving gear and gear transmission disc (if the odometer driving gear is fixed with a hole retaining ring).
Figure 7-40 exploded view of brake drum cover
(5) Disassembly of front disc brake
① The disassembly of the front axle is the same as that of the drum brake. After removing the front wheel, the brake disc must be removed first. The disassembly of the front disc brake is shown in Figure 7-4 1. First, flush the bent tongue of the lock washer, unscrew the fastening bolt of the brake disc and remove the brake disc. The front hub has a perforated retaining ring. After removing the oil seal, remove the retaining ring with needle-nose pliers. Other disassembly is the same as the drum brake front wheel.
Figure 7-4 1 exploded view of front disc brake
② Remove the front brake caliper. As shown in Figure 7-42, unscrew the fixing bolt of the brake caliper mounting bracket, remove the brake caliper, unscrew the bolt plug, then unscrew the brake lining bolt pin, remove the brake lining, unscrew the brake oil pipe bolt and remove the brake oil pipe.
③ The front brake caliper is decomposed. As shown in Figure 7-43, remove the front brake caliper. Unscrew the bleeder bolt from the caliper body to release the brake fluid. Remove the brake caliper mounting bracket, brake pad spring, anti-noise spring and pin sleeve, use an air pump to blow air at the oil inlet hole (high-pressure gas is not allowed), take out the piston, and then remove the dust from the piston.
Figure 7-42 Removing the front brake caliper
Figure 7-43 exploded view of front brake caliper
Ring and piston ring, remove the pin sleeve from the caliper body. When removing the dust ring and oil seal ring, be careful not to damage the piston surface.
(6) Disassemble the front brake master cylinder
The disassembly of the front brake master pump is shown in Figure 7-44. Loosen the bolt, remove the box cover, template and partition, take out the dust cover, take out the retaining ring with pointed nose pliers or blow compressed air from the oil inlet to press out the main pump piston and spring, and remove the first and second piston rings from the piston.
Figure 7-44 exploded view of front brake master cylinder
(7) Maintenance of front drum brake
Figure 7-45 Measuring the Inner Diameter of Brake Drum (Hub)
① Maintenance of brake drum. Measure the inner diameter of the brake drum (hub) with vernier caliper, as shown in Figure 7-45. If it exceeds the specified value, it should be replaced. There are oil stains or scratches on the inner surface of the brake drum, which can be wiped with a rag dipped in paint thinner or polished with emery cloth.
② Maintenance of brake shoes. Check the surface of the brake shoe friction plate. If there is a smooth place, polish it with coarse sandpaper. Measure the thickness of brake shoe friction plate with vernier caliper. If it exceeds the specified value range, replace the brake shoe friction plate.
Measure the thickness of brake shoe friction plate with vernier caliper, as shown in Figure 7-46. If the measured value is less than the service limit, please replace the brake shoes in sets or re-bond the friction plates.
See Table 7-2 for the thickness of friction plate and the inner diameter of brake drum of various motorcycle brake shoes.
Table 7-2 Thickness of Friction Plate and Inner Diameter of Brake Drum of Various Motorcycle Brake Shoes (mm)
Table 7-2 Friction Plate Thickness and Inner Diameter of Brake Drum of Various Motorcycles (mm)-1
③ Brake the camshaft. Long-term use of motorcycle front and rear brakes will cause wear and tear of moving parts, affect braking effect and even brake failure. One of the reasons is that the brake camshaft is worn and the opening size of brake shoe is not enough.
On the premise that the rivet head is not exposed and the friction plate is not damaged, it can be repaired by increasing the thickness of the camshaft and expanding the opening size of the brake shoe.
Prepare a thin sheet of iron (tin can be used) with a thickness of 0.05mm, and cut it into strips with the same width as the camshaft with scissors. The length depends on the wear of the friction plate, and it is generally appropriate to wind the cam twice (layer). After packaging, reset and load the brake, and adjust the free clearance of the brake before use.
(8) Maintenance of front disc brake
① Check the thickness of the brake disc. Measure the brake disc thickness a with a dial indicator, as shown in Figure 7-47. If the measured value is less than the service limit, it means that the brake disc is excessively worn and should be replaced.
② Check the runout of the end face of the brake disc. As shown in Figure 7-48, measure the runout value of the brake disc end face with a dial indicator. If the measured value is greater than the maintenance limit value, it means that the brake disc is deformed and should be replaced.
Figure 7-47 Detecting the thickness of the brake disc
Figure 7-48 Detection of End Runout of Brake Disc
See Table 7-3 for the thickness and end-face runout limits of common motorcycle brake discs.
③ Repair of brake disc deformation. After the front brake disc of motorcycle is deformed, the brake will fail, and there will be scratches and abnormal noise between the brake friction plate and the brake disc.
The deformation of the brake disc is small. The plane of the brake disc can be cut off by 0.5mm on the lathe, or the plane of the brake disc can be ground flat on the surface grinder, and then put on the disc for later use.
If the brake disc is severely deformed, only new parts can be replaced.
Table 7-3 Thickness and End Runout Limit of Commonly Used Motorcycle Brake Disc (mm)
④ Maintenance of brake caliper. Measure the outside diameter of the brake caliper piston with a dial indicator. If the measured value is less than the maintenance limit, it means that the brake caliper piston is excessively worn and should be replaced.
Measure the inner diameter of the hydraulic cylinder with an inner diameter dial indicator. If the measured value is greater than the maintenance limit, the brake caliper hydraulic cylinder is excessively worn and the brake caliper should be replaced.
⑤ Maintenance of the main brake pump. Measure the inner diameter of the main pump cylinder with an inner diameter dial indicator. If the measured value is greater than the service limit value, it means that the main pump cylinder is excessively worn and the brake main pump should be replaced.
Measure the outside diameter of the main pump piston with a dial indicator. If the measured value is less than the maintenance limit value, it means that the main pump piston is excessively worn and should be replaced.
(9) Exhaust of front disc hydraulic brake system
The steps of exhausting the hydraulic brake pipeline are as follows.
Step 1: park the motorcycle on the flat ground, support the motorcycle with the main parking frame, and turn the steering handle to make the brake main pump reservoir in a horizontal state. Then replenish the brake fluid in the reservoir to the upper limit line, and cover the reservoir cover to prevent sundries from falling in.
Step 2: Put the transparent plastic pipe on the bleeder bolt of the brake caliper, and put the other end of the hose into the preset container.
Step 3: Slowly release the brake handle (or press the brake pedal) for several times, then tighten the brake handle (or press the brake pedal), loosen the brake bolt 1/2 turns at the same time, and then pinch the brake handle to the end to make the brake fluid with bubbles flow out along the hose. Then tighten the bleeder bolt and loosen the brake handle (or brake pedal).
Step 4: After a few seconds, repeat the above operation until there are no bubbles in the brake fluid flowing into the container. Then tighten the deflation bolt and cover the deflation bolt cap.
Step 5: Replenish the brake fluid in the oil tank to the upper limit line, then install the diaphragm, diaphragm plate and box cover, and tighten the deflation screw on the box cover.
(10) Installation of front brake handle
As shown in Figure 7-49, loosen the lock nut of the front brake cable, insert the inner wire connector of the front brake cable into the hole of the front brake handle, then install the front brake handle on the right handle switch, fix it with rearview mirror and nut (some motorcycles have special bolts for fixing the front brake handle), insert the inner wire of the front brake cable through the slot in front of the right handle switch, then rotate the adjusting solenoid valve, adjust the free stroke of the front brake handle as required, and finally tighten the lock nut.
Figure 7-49 Installation of Front Brake Handle
(1 1) Front drum brake assembly
① Installation of driving gear of odometer. Apply grease to the inner hole of the front brake drum cover, install the odometer driving gear and the transmission parts of the odometer driving gear, then press the oil seal with tools, and the cutting edge of the oil seal should face the odometer driving gear, and finally install the odometer driven gear.
② Install the brake cam. Apply a small amount of grease to the surfaces of the brake cam and shaft and the supporting pin (fixing pin) of the brake shoe, and then put it into the brake drum cover.
③ Install the brake lining wear indicator. First, install the dust seal on the outside of the brake camshaft (some models have no dust seal), then align the tongue of the inner hole of the indicator needle with the notch groove of the brake camshaft and install the indicator needle.
④ Install the brake rocker arm. Align the printed mark on the brake rocker arm with the printed mark on the end of the brake cam, and then install it. If there is no mark, it should be assembled according to the original assembly position, because only in this way can the brake rocker arm be properly positioned. Some vehicles (such as AX 100) require that the center line of the brake rocker arm and the end face of the brake cam form 14, which is the same as the alignment mark. Finally, tighten the brake rocker bolt according to the specified torque.
⑤ Assembly of front brake drum cover and front hub. Align the boss of the odometer driving gear drive disc on the assembled front brake drum cover with the notch on the end face of the central hole of the front hub, and then install the front brake drum cover.
⑥ Installation of front wheel and front shock absorber. Install the front brake drum cover and the front wheel between the two front shock absorbers. Because the front brake drum cover needs to be fixed, the groove on it must be aligned with the protrusion (or positioning plate) on the front shock absorber. After installing the front axle, if there are fastening bolts, it is necessary to tighten the axle nut first, and then tighten the fastening bolts. Finally, install the cotter pin.
If the front axle is fixed by the axle bracket, first tighten the nut in front of the axle bracket so that the gap between the axle bracket and the front shock absorber remains behind.
(12) Front disc brake assembly
① Connection between brake disc and wheel. After sealing the front wheel bearing with oil, put the mounting surface of the front wheel hub brake disc upward. After cleaning the mounting surface and the brake disc, make the arrow mark on the brake disc face the rotating direction of the wheel, install the brake disc, and then tighten the brake disc fixing bolt (nut) for 2 ~ 3 times according to the specified torque. If there is a locking washer, the bolt (nut) should be locked after the tongue on it is correctly bent.
② Assembly of wheel and front shock absorber. Because the front wheel of the disc brake has no front brake drum cover, the odometer gear is installed in a gear box. When installing the gearbox on the front wheel hub, align the tongue of the odometer driving gear drive plate with the groove on the end face of the front wheel hub, and then install the gearbox and the front wheel hub together on the front shock absorber. Because the gearbox won't turn, it should be stuck. Use the locating plate on the front shock absorber to block the locating plate on the gearbox, and pay attention to the forward rotation direction of the gearbox.
(13) front disc hydraulic brake system assembly
Figure 7-50 Installation of Front Brake Master Cylinder
① Install the front brake master cylinder. As shown in Figure 7-50, combine the front brake main pump with the installation mark on the steering handle, so that the letter marked "UP" on the main pump bracket is upward. Tighten the upper main pump fixing bolt first, and then tighten the lower main pump fixing bolt.
② Install the front brake caliper. Clean the brake caliper with brake fluid (or alcohol) and blow the oil hole with compressed air. Never use gasoline, kerosene and other organic solvents to clean the brake caliper, because the seal is made of natural rubber and cannot contact with organic solvents.
Apply brake fluid to the inner wall of the brake caliper piston hole, and install the piston ring and dust ring. Then coating brake fluid on the outer surface of the brake caliper piston, and installing the bottomed side of the metal piston inward; For resin pistons, install the side with smaller pits inward (less brake fluid is needed for braking).
Install the anti-noise spring, positioning spring and brake lining in turn, press the lining to the piston side (note that the side with friction material faces the brake disc), install a new lock washer, tighten the positioning bolt pin, then bend the tongue on the lock washer to lock the positioning bolt pin. After applying brake fluid to the bolt pin and sliding pin, install the brake caliper body with combined brake linings on the brake caliper mounting frame.
Install the copper washer, brake washer and brake oil pipe on the clamp body, screw on the oil pipe bolt, then install the assembled clamp body on the front shock absorber, tighten the bolt and turn the front wheel. There should be no delay. The clearance between the brake caliper bracket and the brake disc shall be not less than 0.7mm..
(14) Emergency Maintenance of Brake Wire Rope after Elongation
The brake wire rope used to control the brake will be stretched after a period of time. When adjusting the brake, even if the nut is screwed to the end, the brake cannot be effectively braked. At this time, you can add a few gaskets under the nut, and the problem will be solved.
(15) Emergency repair of brake handle damage during driving.
For a motorcycle with front wheel drum braking, the structure and size of the brake handle and the clutch handle are basically the same, and they can replace each other if necessary. When the brake handle is damaged, if there are clutch fittings, it can be replaced (if the clutch handle is damaged, the front brake handle can also be replaced).