How should the self-adjusting arm of the trailer axle be used and maintained?

Brake system is a whole system, brake pump, self-adjusting arm, camshaft, brake, brake drum and a series of parts depend on each other and influence each other. When analyzing and dealing with various problems of the self-adjusting arm, it is not possible trailer axle to treat the head with headache and the feet with pain.

The cause analysis of unqualified brake clearance

Self-adjusting arm: improper gap matching, preset gap value is not accurate; The product consistency of self-adjusting arm is poor, and the adjustment accuracy is unstable; The self-adjusting arm is not properly installed on the vehicle;

Brake drum: the brake drum processing accuracy is not appropriate, the internal control is not round, the circle runout value is too large; The material and structure of the brake drum are not suitable, the thermal expansion rate is abnormal, the overall stiffness is poor, and it is easy to deform. The brake drum is not properly mounted, both internal and external. They all rotate synchronously with the hub coaxial connection. When not properly installed, the brake drum will be abnormally unbalanced.

Brake: brake assembly stiffness is poor, including camshaft, brake shoes, etc.; The thermal expansion rate of the friction sheet is abnormal, and the thermal expansion is abnormal. The abnormal fit of camshaft, brake shoe and brake plate causes the outer circle of brake surface of friction plate to be out of round.

Vehicle/axle: axle housing coaxiality is abnormal, the overall rigidity is poor; Wheel end bearing clearance is too large, the wheel hub can not rotate around the axle axis normally;

Self-adjusting arm daily maintenance requirements

1. The vehicle should fill butter (No. 2 lithium grease) in the injection nozzle of the self-adjusting arm once per 20,000 km operation;

2, in daily use, when the brake is weak, it is recommended to detect the counterclockwise torque of the hexagonal head of the self-adjusting arm worm. Rotate once, if the measured minimum torque is less than 18Nm, it indicates that the self-adjusting arm has been damaged, and it must be replaced in time;

3. Check whether the control arm is stable and fixed. Due to trailer axle excessive wear of the control arm bushing and loose locking bolts of the control arm, the self-adjusting function will fail.

The typical use mistake of self-adjusting arm

First, in the daily maintenance of the vehicle because the brake gap is too small, heat failure, and often use a wrench to rotate the worm "hex" counterclockwise, in order to amplify the brake gap value.

Misunderstanding guidance: The self-adjusting arm stipulates that manual rotation of the worm hexagon head is allowed only during installation, disassembly and detection, otherwise it will directly lead to early wear of the internal mechanism of the self-adjusting arm, and the problem of weak braking of the vehicle in subsequent use.

Correction method: try to avoid twisting the worm "hexagon" in daily maintenance, extend the service life of the self-adjusting arm, in the case of vehicle brake gap is too small, should check in time whether the self-adjusting arm model is correct, self-adjusting arm installation is in line with the brake problem.

Second, the vehicle has the phenomenon of slow brake reset and drag brake, which is judged to be caused by the internal stagnation of the self-adjusting arm, and the self-adjusting arm is required to be replaced.

Error guidance: The self-adjusting arm only conducts the thrust of the air chamber in the vehicle brake system, and ensures the brake gap value between the brake shoe and the brake drum. The self-adjusting arm is installed on the camshaft, and there is no reset power after braking. The brake reset is completed by the return spring of the brake shoe and the return spring of the air chamber.

The correction method is: when the above problems occur in the vehicle, it should be timely checked whether the installation of the self-adjusting arm is in line with (especially the axial clearance), and whether there is a problem with the return spring of the brake branch pump, the return spring of the brake, and the coordination of the S camshaft and the roller.

The simple determination method of self-adjusting arm function failure

In the case of improper installation of the self-adjusting arm, use the wrench of SW12 to turn the worm hex head counterclockwise and greater than 180° to enlarge the gap between the brake drum and the shoe (do not use pneumatic or pneumatic tools).

When the brake pressure of the whole vehicle is ≥0.6MPa, the trailer axle brake is applied several times, and the hexagonal head of the worm is observed to rotate clockwise, it is judged that the self-adjusting arm functions normally and can be used normally.

Self-adjusting arm common fault analysis

Brake heating fault analysis flow chart

Brake weakness fault analysis flow chart