Withdrawal
Pic. 6.22. Front disc brake: 1 - connecting tube (brake hose and tube assembly); 2 - front brake caliper assembly; 3 - brake disc
Front disc brake components are shown in fig. 6.22.
Checking and replacing the front disc brake pads
Pic. 6.23. Technological openings of a support
Check the thickness of the brake pads through the technological holes of the caliper (pic. 6.23).
Attention! If the thickness of the brake pad lining is less than the maximum allowable value, then replace the brake pads on the left and right wheels as a set.
If there is a noticeable difference in the thickness of the brake pads on the left and right sides of the caliper, then check the smoothness of the movement of the caliper along the bushings of the guide and locking fingers.
Remove the guide pin, lift up the caliper assembly and hang it with a wire.
Note. Be careful not to smear the lock and guide pins with grease.
Pic. 6.24. The procedure for removing parts from the caliper: 1 - brake shoe and indicator assembly; 2 - brake shoe assembly; 3 - retainer; 4 - outer gasket
Remove parts from the caliper in the order shown in Figure 6.24.
Checking the thickness of the brake disc
Pic. 6.25. Measuring the thickness of the brake disc
Using a micrometer, measure the thickness of the brake disc at eight points approximately every 45°at a distance of 10 mm from the outer edge of the disc (pic. 6.25).
Brake Disc Thickness:
- nominal value - 26 mm;
- limit value: 24.4 mm.
Note. The change in thickness is made at least 8 points.
If the thickness of the disc does not meet the maximum allowable value or the disc is unevenly worn, then remove it and install a new one.
Front brake disc runout check
Pic. 6.26. Removing the brake caliper
Remove caliper assembly, lift and secure out of the way with wire (pic. 6.26).
Note. Tighten the wheel nuts to secure the brake disc to the hub.
Pic. 6.27. Measuring brake disc runout
Install a dial gauge approximately 5mm from the outer edge of the brake disc and measure disc runout (pic. 6.27).
Limit value: 0.04 mm.
Brake disc runout correction
If the amount of runout of the brake disc meets or exceeds the limit value, then try to change the relative position of the disc and the wheel hub, and then measure the runout again.
Pic. 6.28. Marking locations
Mark both sides of the wheel stud with chalk before removing the brake disc at the point of maximum runout (pic. 6.28).
Pic. 6.29. Measurement of axial clearance in the hub bearing
Remove the brake disc and set the dial gauge as shown in Figure 6.29. Moving the hub in the axial direction, measure the axial clearance in the hub bearing.
Limit value: 0.05 mm.
If the end play is equal to or greater than the limit, remove the hub and check the steering knuckle and hub.
Pic. 6.30. Re-measurement of brake disc runout
If the axial clearance in the hub bearing does not exceed the maximum allowable value, then turn the brake disc 180°from the chalk line, install it on the hub, and again repeat the measurement of the brake disc runout (pic. 6.30).
If the performed operations have not eliminated the increased runout of the disc, then it is necessary to replace the brake disc.
Installation
Install the brake pad retainers.
Pic. 6.31. Brake pad retainers
Install the brake pads into the brake pad retainers (pic. 6.31).
Note. All four brake pads must be replaced as a set.
Note. When replacing brake pads, check for deformation. When replacing brake pad retainers, install a new or used retainer only after it has been cleaned of foreign particles.
Insert the piston into the working brake cylinder using a special tool or using the handle of a plastic hammer.
Carefully install the caliper assembly so as not to damage the piston boot.
Tighten the two guide pins to a nominal torque of 22–32 Nm.