Achieving the optimum running clearance between the brake pad and disc will help avoid overheating.
Brakes can overheat for a number of reasons. One of the most common, and most easily solved, is the incorrect setting of the running clearance between the brake pad and disc. This can lead to the following problems:
- When clearance is set too high, it is likely to result in poor brake performance due to the pad not completely meeting the disc to achieve full friction.
- When the clearance is set too low, the brake pad and disc meet, causing friction and so overheating the brake system, resulting in poor brake performance, brake judder, noise, and even permanent disc damage.
REGULAR TESTING OF RUNNING CLEARANCE
We recommend you check running clearance regularly, because as pads and discs wear, the clearance steadily increases. All air disc brakes are fitted with an automatic adjuster which self-adjusts during brake applications to accommodate for brake pad and disc wear. However, they must still be checked regularly to ensure they are maintaining proper push rod travel.
Once an adjuster has been properly installed, automatic adjusters should not need manual adjustment. They should be routinely checked by a mechanic at each brake pad change or if the brake is running hot. If an automatic adjuster is found to stroke beyond the maximum allowed, this usually indicates there are other brake problems that need to be addressed.
Here is the brake adjustment procedure
- Ensure the brakes are disengaged, and that the vehicle is blocked to ensure it does not roll.
- Remove the wheel.
- Press the caliper assembly inboard on its guide pins. Press the inboard pad away from the tappets and check both the tappets and the inboard pad back-plate.
- Check the running clearance with a feeler gauge between tappets and inboard pad back-plate, and it should be in the range described in the table below.
- If the running clearance is smaller or higher than the correct value shown in the table below continue the procedure as follows.
- Set the running clearance at 2mm.
- Apply the brakes 50 times.
- Check the running clearance again with a feeler gauge, and it should be in the range described in the table below.
- If the running clearance is still smaller or higher than the correct value shown in the table below, either the entire brake or the housing only will need to be fully replaced according to the brake manufacturer’s manuals.
RECOMMENDED RUNNING CLEARANCES BY BRAKE SYSTEM
|Manufacturer||Type||Running Clearance (MM)|
|KNORR-BREMSE||SN5000||0.6 - 1.1|
|SB6000||0.6 - 1.0|
|SN7000||0.6 - 1.1
|SN7000 for Scania||0.5 - 1.0|
|SK7000||0.6 - 1.0
|ARVINMERITOR||D-Elsa1||0.5 - 0.7|
|D3||0.6 - 0.8|
|D-Elsa2||0.6 - 0.8|
|HALDEX||DB19 with 10mm thrust plate||0.6 - 0.9|
|DB19 with 6mm thrust plate||0.8 - 1.2|
|DB22LT||0.6 - 1.2
|DB22 with 10mm thrust plate||0.6 - 0.9|
|DB22 with 6mm thrust plate||0.8 - 1.2|
|WABCO||PAN17||0.6 - 0.9|