Monday, February 6, 2012

How to inspect,service and replace brake shoe liner?

Brake Shoe Lining Operation:

Its a special friction material that will withstand high temperature and pressure, used for lining the brake shoes or pads, either by riveting or bonding.

This is how basic brake shoe lining looks :----

Before replacing brake shoe liner first inspect it.
If it looks dirty then servicing will help.If it looks worn out,then it has to be replaced.

See below all the three procedure with details.
that is 

1) Inspect.
2) Servicing.
3) Replacement.

INSPECT:---
  • Inspect the linings for uneven wear, imbedded foreign material, loose rivets, and to see if they are oil soaked. If linings are oil soaked, replace them.
  • If linings are otherwise serviceable, tighten or replace loose rivets, remove imbedded foreign material, and clean the rivet counterbores.
  • If linings at any wheel show a spotty wear pattern or an uneven contact with the brake drum, it is an indication that the linings are not centered in the drums. Linings should be circle ground to provide better contact with the drum.
Service:---
Several different methods are used to mount the drum to the wheel hub flange.
  • It can be fastened with rivets or by swaging the piloting shoulders of the wheel studs, or with speed nut fasteners installed over the threads of the wheel studs.
  • The most common mounting method is to use the tire rim and lug nuts. The drum is a slip fit over the axle flange and studs. Speed nuts are installed at the vehicle manufacturing plant for temporary retention of the drum on the assembly line until the wheel is installed.
  • A floating drum can be retained by a nut and cotter pin. The drum can also be secured to the axle flange by one or two bolts. Some import applications have two additional holes threaded into the drum face so bolts can be used to press the drum from the hub or flange.
  • After removing the retaining devices that hold the drum to the axle flange or hub, the drum can be removed for servicing.
  • If the brake drum is rusted or corroded to the axle flange and cannot be removed, lightly tap the axle flange to the drum mounting surface with a plastic mallet.
  • Remember that if the drum is worn, the brake shoe adjustment has to be backed off for the drums to clear the brake shoes.
  • Do not force the drum or distort it. Do not allow the drum to drop.
  • If the brake shoes have expanded too tightly against the drum or have cut into the friction surface of the drum brake, the drums might be too tight for removal. In such a case, the shoes must be adjusted inward before the brake drum is removed.
  • On most cars with self-adjusting mechanisms, reach through the adjusting slot with a thin screwdriver (or similar tool) and carefully push the self-adjusting lever away from the star wheel a maximum of 1/16 inch (1.5 mm).
Backing off the self-adjusters in order to remove the drum brake.
  • While holding the lever back, insert a brake adjusting tool into the slot and turn the star wheel in the proper direction until the brake drum can be removed.


REPLACE:---
Brake Relining
  • Brake linings that are worn to within 1/32 inch (0.79 mm) of a rivet head or that have been contaminated with brake fluid, grease, or oil must be replaced.
Potential brake shoe problems. Courtesy of Wagner Brake Products.
  • Failure to replace worn linings results in a scored drum. When it is necessary to replace brake shoes, they must also be replaced on the wheel on the opposite side of the vehicle. Inspect brake shoes for distortion, cracks, or looseness. If these conditions exist, the shoe must be discarded.
  • Do not let brake fluid, oil, or grease touch the brake lining.
  • If a brake lining kit is used to replace the linings, follow the instructions in the kit and install all the parts provided.
  • The two general methods of attaching the linings to the brake shoes are bonding and riveting.
  • The bonded linings are fastened with a special adhesive to the shoe, clamped in place, then cured in an oven. Instead of using an adhesive, some linings are riveted to the shoe.
  • Riveted linings allow for better heat transfer than bonded linings.
Drum Shoe and Brake Installation
  • Before installing the shoes, be sure to sand or stone the inner edge of the shoe to dress down any slight lining or metal nicks and burrs that could interfere with the sliding upon the support pads.
  • A support (backing) plate must be tight on its mount and not bent. Stone the shoe support pads brightly and dress down any burrs or grooves that could cause the shoes to bind or hang up.
  • Using an approved lubricant, lightly coat the support pads and the threads of servo star wheel adjusters. On rear axle parking brakes, lubricate any point of potential binding in the linkage and the cable. Do not lubricate nonservo brake adjusters other than to free a frozen adjuster with penetrating oil.
The areas or pads where the brake show will rub or contact the backing plate. Courtesy of Daimler Chrysler Corporation.
  • Reassemble the brakes in the reverse order of disassembly. Make sure all parts are in their proper locations and that both brake shoes are properly positioned in either end of the adjuster.
  • Also, both brake shoes should correctly engage the wheel cylinder pushrods and parking brake links.
  • They should be centered on the backing plate. Parking brake links and levers should be in place on the rear brakes.
  • With all of the parts in place, replace the brake drum.

This details will help.
Thanks.

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