Conducting a complete brake job, from start to finish
September 1, 2005
TORONTO, Ont. - The following instructions have been provided by Haldex. Haldex is providing preventive maintenance tips and advice to help you maintain and service your brake systems to keep them ope...
GIMME A BRAKE: Haldex says doing a little detective work can really pay off when it comes to knowing your brake system and keeping safe on the road.
TORONTO, Ont. – The following instructions have been provided by Haldex. Haldex is providing preventive maintenance tips and advice to help you maintain and service your brake systems to keep them operating at peak levels of performance for better efficiency and safety.
In conducting a complete brake job, disassembly can impact the assembly portion of the brake job process – all of which affects overall performance of your brakes.
Be sure as you disassemble the brake to inspect every part carefully, checking for unusual wear. In fact, a little bit of detective work pays off in the long run. Part wear patterns can tell you a lot about the brake and the entire braking system.
First, before pulling the wheels, check for any sign of endplay. Endplay is an indication of seal problems or excessive bearing or cup wear. After pulling the wheels, inspect all shoes for even wear. And, compare the wear patterns. If there’s a pattern of uneven wear it could be a sign of excessively worn, failed or misadjusted components that you’ll have to correct before you re-assemble the brakes.
Moving to the linings, it is important to pay close attention for signs of heat-checking within the lining. If you see signs of heat-checking on some linings and not others, you’ll know that the wheels are not braking evenly. If you find heat-checking on all the linings, this could indicate that the wrong lining is being used for that particular application, that the vehicle is being overloaded or a combination of both of these factors. Another thing to check for at this stage of the process is an uneven pattern or excessive grooves. To see these clearly look across the lining surface. Uneven patterns may indicate bent spiders or bellmouth drums.
Also, make sure that there is never any grease or oil on the lining or the brake shoe. Be sure to not re-use a greased or oil soaked brake shoe. Grease or oil migrating to the friction material will cause the lining to glaze and either not perform in balance with the other wheels, or fail completely.
To maintain balance, it is important that you never do a one wheel brake job unless the lining is less than 10 per cent worn. If you must do a one wheel brake job, however, be sure to use the exact same linings from the same manufacturer.
Inspection of drum surfaces is also important. Look closely at each drum for signs of even wear, glazing or signs of heat-checking.
Heat checks, cracks and blue spots indicate excessive heat. Note that heat-check lines over one inch are not normal. It is important to note that you should never reuse a drum if wear is over .080, if several heat-checks are aligned across the surface of it or the braking surface shows hard spots.
Next, inspect the s-cam for wear at the bushing, at the head and around the spline. A wheel with a worn s-cam or a worn s-cam bushing is probably not doing its share of the braking and needs adjustment, repair or replacement.
Make sure to check the brake adjuster for proper settings and operation. Also inspect clevis pins and brake adjuster bushings for signs of wear. If there’s wear of over .030, replace both.
Be sure that you never mix automatic brake adjusters with manual brake adjusters. And, never mix different makes of automatic brake adjusters on the same axle.
Compare the amount of wear on the front axle shoes against the wear on the rear axle shoes when relining either a truck or trailer. If the wear is unequal, you’ll know that there’s an air timing imbalance or a mix of different rated friction materials. Also, you’ll want to check for inconsistent use of elbows in airlines. Keep in mind that a 90 degree elbow is the equivalent of 7′ of extra hose!
Finally, as you complete disassembly procedures, inspect spiders. Pay close attention to the anchor pinhole area and look for squareness.
Before beginning the re-assembly process, it is important to make a proper selection of friction material for the application at hand. Consider load, position of the load and the terrain over which the vehicle will be operating when selecting friction. If you have any questions about friction material, its application or ratings, consult your friction supplier.
They’ll be able to point you in the right direction in choosing the right lining for the job. It’s also important to pay close attention to shoes, as today many shoes look alike, especially shoes with the new extended service design. Make sure that you always install the same shoe as the one that was removed.
The first step in re-assembly is replacing all shoe attaching parts: anchor; pin bushing; cam bushings; and oil seals. Any parts that will be re-used should be thoroughly cleaned with solvent, rinsed and dried. Be sure to replace s-cams, bearing and cups, as necessary.
While it is important to lubricate anchor pins, brake roller and the bushing areas of the camshaft, you should take extreme care not to lubricate or get any lubricant on the face of the roller, which is the contact point with the s-cam. Make sure you only lubricate the bearing area of the roller that contacts the shoe web.
If necessary, install new drums according to the wear guidelines set down in the disassembly procedure. When installing new drums make sure you’re not mixing light and heavy-duty drums together. Mixing light and heavy-duty drums will result in uneven brake shoe wear, and poor performance.
Be sure to lubricate axle shafts to ensure that hubs slide on easily. Be sure to slide hubs onto the axle far enough to be able to install the outer bearing and the inside axle nut. Don’t, under any circumstances, slam the hub onto the axle! Adjust bearings to the manufacturer’s specifications and install spacers and outer nuts, when applicable, as well as a new hubcap gasket.
Always, after re-assembly, make sure that you adjust every brake adjuster on every wheel on the vehicle. Shoes should be adjusted as close to the drums as possible, without dragging. Adjust all manual slacks of .015 drum clearance. Automatic brake adjuster drum clearance is .018 – .025, but be sure to check the manufacturer’s specifications to make sure you have the correct clearance. Follow the same procedure for each brake adjuster.
Finally, inspect all brake hoses leading to the chambers, and replace them if you find any cracks. You’ll also want to inspect all the spring brakes for center seal leakage, replacing them if necessary. Check brake release. If it’s slow on the trailer, you’ll want to install a quick release gladhand on the service side of the trailer. Set push rode stroke to correspond with the chamber size and the brake adjuster’s exact specifications. If you have to replace any brake chambers, make sure that you don’t mix sizes or allowable strokes. Make sure you never mix a long stroke chamber with a short stroke chamber.
When relining a tractor, be sure to replace air governor with cut in/out of 105/120 psi. When relining a trailer, be sure to replace both glad hand seals.
Always road test the vehicle to “break-in” new linings. Here’s a good sequence to follow:
* Perform 10 snubs, decelerating from 40 mph to 20 mph;
* Make 10 stops from 20 mph, applying moderate air pressure;
* Perform two stops from 20 mph with a full application of air pressure.
After you’ve performed your road test, re-examine each wheel for excessive end-play. Re-check slacks and chambers for proper and equal stroke. Your brake job is now complete.
– Technical article supplied by Haldex Brake Systems Division.
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