Top 10 Foundation Brake Problems

1.) Cam Bushings
Bushing wear that allow the cam head to drop can allow the bottom show to drag on the drum. Additional push rod travel will be used up centering the shoes inside the drum before applying equal force. Worn cam bushing also increases the output of the brake and can therefore cause more rapid lining and drum wear. Bushings should be properly lubricated and replaced at each reline.

2.) Return Springs
Broken or weak return springs can allow the bottom shoe to rub on the drum when no brake application is being made. Brake release is dependent upon the return spring being strong enough to pull the brake shoes back to the release position. Weak / broken springs can allow the brakes to drag.

3.) Brake Shoes
Brake shoes should be checked for proper crown or arc at the shop table. Constant reuse of shoe "core" can cause stretching, poor contact and aggressive brakes. Shoes should be re-arced or replaced if not within specification.

4.) Rollers
Rollers transfer the applied force from the cam head to the shoe. Flat spots on the roller will interrupt this movement and could cause a sliding motion that can damage the cam head. The trailing shoe drives the roller into the cam head causing more wear on that particular roller.

5.) Anchor Pins
The anchor pins secure the shoes on the spider. The leading shoe is drive against the anchor pin causing wear on the pin and the bushing in the spider, which can cause uneven shoe wear and brake noise.

Related: Some Quick Brake Maintenance Tips

6.) S-Cam
The S-Cam will wear in the bushing area if not lubricated properly. Wear in this area will not allow a snug fit in the bushings. Flat spots on the cam head will interrupt the movement of the shoe into the drum.

7.) Adjustment
Brake adjustment is a major cause of premature lining wear and drum distress. With all other factors being the same, i.e. chamber size, slack length, brake lining, the shortest push rod stroke will do more braking until it matches the next shortest, etc. This result in accelerated wear of the brake linings and more thermal fatigue of the brake drum on the brakes with the shortest strokes. The opposite is true of the longer stroke brakes. This results in unfavorable comparisons in lining and drum life. This is most evident when one brake wears more than the brake across the axle or one axle set of brakes wears out before its mate on the tandem. When automatic and manual slack adjusters are mixed on mating equipment, the adjustment frequency should be increased on the manual slacks. Also, automatic slack adjusters should be regularly checked to assure they are functioning properly.

8.) Slack Adjusters
Adjusters should be checked for internal wear. The worn gear can wear which will allow movement of the adjuster without corresponding movement of the S-Cam. The clevis bushing in the adjuster should be replaced at each reline. Adjusters must be of the same effective length (center of the S-Cam to center of clevis pin) across the axle and each axle set.

9.) Air Chambers
Service chambers must be of the same size across the axle and within each ale set. Push rod actuation should be straight out of the chamber. Elongation of the hole in the chamber face indicates a problem which should be corrected. Push rod lengths should be equal. Spring brakes can cock internally allowing partial brake application resulting in dragging brakes. Service chamber return springs break or become weak allowing the push rod to cock or fail to fully retract upon release causing brake drag. Check out our air brake chambers for sale.

10.) Drum Condition
Drums that are scored, out-of-round, severely heat checked or in generally poor condition will accelerate lining wear due to poor lining-to-drum contact. Worn drums have less material to act as a heat sink resulting in high temps and shorter lining life. With the S-Cam brake, a worn drum can shift the initial lining contact from the center of the shoe to the cam end, increasing lining wear on the cam end. This can shorten lining life on the brake by not allowing full lining volume to be consumed. Check out our drums for sale.