The traveling braking system of cpcd5a Ⅱ Z forklift consists of vacuum pump, vacuum tank, vacuum booster, brake master cylinder, brake slave cylinder, wheel brake and brake pedal. The braking type is vacuum pressurization, hydraulic drive and internal expansion front wheel braking. Common faults are as follows.
1. When the brake pedal is pressed, it does not have braking effect
Possible cause: there is no oil in the brake master cylinder; The brake system pipeline leaks oil; The leather cup of the master cylinder is broken and worn, resulting in oil leakage; The master cylinder piston leather ring is damaged, swollen or worn too much; The master cylinder piston leather ring is installed reversely; Oil leakage of the slave cylinder piston or damage of the half shaft oil seal, resulting in oil contamination in the brake drum, resulting in brake failure of the brake drum and friction lining; The brake shoe friction lining is worn too much, which makes the rivets exposed or loose.
2. When stepping on the brake pedal, there is elastic resistance and insufficient braking force
Possible cause: there is air in the braking system; Insufficient brake fluid in master cylinder; The oil return valve of supercharger is damaged or dirty; The brake fluid cannot build up enough pressure, and the brake cannot be applied even if the brake pedal is pressed to the bottom; The clearance between brake drum and friction lining is too large; Brake shoe looseness, etc; Incorrect installation of brake shoes and improper adjustment of brake clearance.
3. The brake pedal has rebound force and the braking effect is poor
When stepping down the brake pedal, check whether the vacuum supercharger has the "Shh Shh" sound of air intake. If there is no such sound, loosen the low-pressure oil pipe of the supercharger, and then step on the brake pedal. If the oil pipe does not discharge oil or the oil discharge is weak, the oil circuit from the master cylinder to the vacuum supercharger is blocked, or the master cylinder works poorly, otherwise the supercharger itself is faulty.
Possible cause: if the pipeline is blocked, remove the low-pressure oil pipe from the master cylinder to the supercharger and blow it with compressed air. If it is blocked, the pipeline is blocked; Otherwise, the master cylinder is not working properly. The poor performance of the master cylinder is that the oil outlet pressure is low (the standard is 3Mpa, which can be measured with a pressure gauge), and the leather cup and leather ring of the master cylinder swell; The oil outlet valve works poorly, or there is no gap between the master cylinder push rod and the piston, blocking the oil return hole, so that the brake fluid cannot return to the oil storage chamber; The leather ring of the supercharger control cylinder expands. When the brake pedal is released, the piston cannot return quickly. When the brake pedal is continuously pressed, the pedal does not return and gradually rises. It feels very hard when pressed down; The oil inlet hole of the supercharger control cylinder is blocked, and the atmospheric valve cannot be opened when stepping on the brake pedal, so it does not pressurize; When the sealing ring of the intake valve expands or leaks, the position of the brake pedal will become higher and feel very hard when stepping on. When the forklift is walking, the four wheels drag.
4. Brake drag, brake drum heating after long-time walking
Possible causes: the supercharger parts are stuck and the brake stroke is not adjusted properly; The oil return hole of the brake master cylinder is blocked (covered by an inflated leather cup or blocked by dirt in the brake fluid), resulting in poor oil return and wheel braking drag; The brake fluid is dirty and the oil return is too slow; The leather cup of the master cylinder swells, and the leather cup cannot return quickly after the brake pedal is released; The sealing ring of the control valve expands, so that the air valve is not closed tightly, the exhaust of the air chamber in the tympanic membrane of the power cylinder is delayed, and the tympanic membrane cannot return quickly; The copper pipe between the brake master cylinder and the supercharger is deformed or flattened, resulting in slow oil return speed and brake drag.
5. Unstable braking
Possible causes: the brake drum is out of round, and the clearance between the brake drum and the brake shoe is abnormal; Brake shoe adjustment is not correct
6. It's hard to step on the brake pedal.
Possible cause: the master cylinder leather cup or master cylinder piston leather ring is swollen; The copper pipe between the master cylinder and the supercharger is deformed or flattened, resulting in smaller inner hole and poor oil flow; The copper pipe leading to the wheel cylinder is deformed, resulting in smaller hole diameter and poor oil flow; Control the expansion of cylinder leather ring; The brake fluid deteriorates and is too viscous, resulting in poor fluidity.
7. Brake deviation
Possible causes: the braking force of the left and right wheels is unbalanced, which makes the forklift deviate to one side during braking (the braking clearance or wheel cylinder condition of which side should be checked if the side grabs forward during braking; the deviation is irregular, and the left and right are ignored. If the left and then the right are braked, the braking condition of the left wheel should be checked first, otherwise, the braking condition of the right wheel should be checked first); Or there is oil stain on the brake shoe friction plate or brake drum.
8. Oil leakage (including external and internal leakage)
If there is any oil leakage in the master cylinder, slave cylinder, supercharger and pipeline, the braking efficiency will be reduced or the braking will be completely ineffective.
Possible causes: the oil leakage of master cylinder and slave cylinder is mostly due to the leakage caused by wear and tear of leather cups and rings after they have been used for too long; If it feels light when stepping on the brake pedal, it is generally the wear and oil leakage of the master cylinder cup; Poor sealing of the booster cylinder piston cup, leather ring or piston push rod leather ring and control valve cup will cause oil leakage; The brake shoe is too thin or the brake clearance is too large. When the brake pedal is pressed hard, the wheel cylinder cup will often turn over and cause oil leakage.
9. Excessive brake oil consumption
Possible cause: oil leakage of pipeline; The brake slide valve cup in the transmission shift control valve leaks oil into the transmission. At this time, the smell of brake oil can be heard from the transmission oil quantity inspection hole. Check it to confirm whether there is brake oil leakage; The poor sealing of the piston cup, leather ring or piston push rod leather ring of the booster cylinder of the vacuum booster and the leather cup of the control valve will cause excessive consumption of brake oil. When the booster booster booster chamber is opened, the brake oil will leak out. In serious cases, it will leak into the engine oil pan through the lubricating oil pipe of the vacuum pump, and the oil will be diluted or sucked into the cylinder and burned.
10. Failure of vacuum booster
This kind of fault can be judged by whether the supercharger has air intake or not and detecting the brake oil pressure at the brake wheel cylinder.
Possible cause: the supercharger works normally, and the oil pressure at the brake cylinder should reach 11 ~ 13Mpa (which can be detected by pressure gauge). If the pressure is lower than this value, the supercharger is faulty; Remove the vacuum pipe of the supercharger, block the pipe orifice by hand, and start the engine for a moment. If you feel no suction or little suction, there is air leakage in the vacuum tank and vacuum pipe, or the vacuum pump works poorly; The working condition of the vacuum pump can be detected by the vacuum gauge. The normal vacuum value should be -0.08-0.085mpa. If it is lower than this value, the vacuum pump is faulty. After inspection, the vacuum pump, vacuum tank and vacuum pipe are normal, and the supercharger still does not work, it is caused by the serious blockage of the air filter of the vacuum supercharger (this fault often occurs because the supercharger air filter of the machine is directly installed on the supercharger and located under the vehicle, and the working environment is poor), or the air valve cannot be opened, so that the atmosphere cannot enter the booster chamber.
