How to Adjust Air Brakes
If your braking is soft or grabs on the disc, you may need to adjust the air brakes. This is not a difficult job and can be accomplished in a few minutes if you are confident and know what you are doing, as air brakes are not the same as disc brakes. Other brake problems can be noted at the same time. Adjustment should really be done in a garage where you can safely lift the wheels off the ground. If you are on the open road, it might not be safe to carry on until you reach a garage.
Step 1 - Release the Air
Park on level ground and chock the wheels so the vehicle does not move while you are adjusting the brakes. The air brake system must be at full pressure. Lower the emergency brake, then release the brakes by pushing in the air valve. Note which brake chamber you are adjusting. You will have to try to keep each push rod at the same distance so each wheel's stopping ability is close to the same.
Step 2 - Check the Push Rod
Mark the location on the push rod where it leaves the chamber. Pull the push rod out of the brake chamber using a ratchet wrench or suitable tool. A ratchet wrench is used for ratcheting-style nuts. Measure from the chalk line to the brake chamber which will show the stroke range. If it is over a 3/4 inch it means that your brakes need adjusting.
Step 3 - Adjust the Push Rod
The manual slack adjusters are found on the air canister, which is on the axle housing. Check your manual for more precise instructions. Turn the adjuster; the s-cam will turn in the direction of rotation when the brakes are applied. If you are turning it the wrong way, the push rod will be pulling out of the air chamber and you will get a lot of free play. When you have discovered the proper direction, continue tightening until you get some resistance. The brake linings have now met to the drum. You now need to reverse the adjuster bolt about half a turn to obtain some distance between the drum and lining. If you cannot tell the difference between tightening and loosening when turning the bolt in both directions, the slack adjuster needs to be replaced.
Although they need no manual adjustment, you can catch brake issues in time if you check to make sure that the adjustment of the automatic adjusters is maintained. Pressing the brakes completely and then releasing at least six times will test the brakes and allow the adjusters to fix themselves if needed. If the stroke of the push rod is excessive after this process, you can manually adjust the brakes to get you to a repair facility. Making an adjustment is only temporary and they will revert to their intended stroke in time.