1999/03/29 Caterpillar

All Off-Highway Trucks, Tractors and Quarry Trucks

The criteria for replacement of brake discs, plates and dampers at the time of an unscheduled repair or rebuild has been updated. Each circumstance is unique, but inspection and replacement at these times can lower the number of repeat failures and improve rebuild component reliability of brake packs.

The reuse of worn brake discs, even those within specifications, can still cause the brake piston to stroke beyond the limits of the seals when reassembled in a brake pack.

"Warped", "glazed", and/or "burnt" discs that exhibit signs of excessive temperatures should be replaced in all instances.

All brake dampers should be replaced during a brake rebuild due to shrinkage and deterioration of the damper material.

Disc Replacement Guidelines

Replace:

* If it has over 20% more wear than the other discs in a brake pack

* If more than 10% of the friction material has "flaked" off

* If the friction material appears to be very easily chipped when using a light prying force with a knife point

* If damaged by contamination of lubricating oil with water

Examples:

* It is not acceptable to reuse any disc with 70% life remaining with new discs which have 100% life remaining.

* It is not acceptable to use a combination of worn discs with 60%, 70% and 90% life remaining.

NOTE: The reuse or replacement of only a selected number of worn or damaged brake discs may result in uneven wear and unequal brake cooling flow (heat dissipation) across the reused brake discs. Unequal brake cooling oil flow may occur between the disc and plate due to the different brake cooling groove depths found in reused brake discs. The increase in brake temperature across each individual brake disc can lead to brake disc glazing, resulting in higher loads to those brake discs that were replaced at the time of rebuild. This can cause premature failure and/or shorter overall component life.

Plate Replacement Guidelines

Replace:

* If it is worn to less than a minimum thickness of 2.29 mm (.090 in)

* If more than 10% of surface area is scored

* If there are deep radial grooves that could cut the friction material

* If it is warped. A plate is considered warped if it cannot be flattened by applying a 90 N (20.0 lb) force on the plate.

Illustration 1.

(A) 90 N (20.0 lb) weight.

(B) Plate.

(C) Flat top table.

(D) A 0.038 mm (.0015 in) feeler gauge should not fit between the plate and weight or table.

Tooth Wear Guideline

Disc assemblies should be inspected for tooth wear. Some tooth wear is acceptable, but never reuse a disc assembly that has obvious notches worn into the teeth.

Illustration 2.
Shows shallow wear but no obvious step.

NOTE: Use again.

Illustration 3.
Shows notches worn into teeth.

NOTE: Do not use again.

Installation/Reassembly

The disassembly and reassembly of worn brake discs oriented differently within the brake pack and running on the brake hub can result in brake disc tooth damage. Brake disc teeth located over the lubrication slots of the hub will not wear the same as those located between the hub splines. When discs are reoriented, the teeth with the least wear will then become more heavily loaded and may break off from normal brake application. This practice can reduce component life and reliability.

Parking Brake Holding Ability Test

The parking brake holding ability test is intended to determine if the braking system is meeting the required specifications. The tests are not intended to sustain a machine at a specific engine RPM. The parking brake holding ability test should be performed daily. The following chart outlines the specific engine RPM's that should be used in the test:

NOTE: Refer to the parking brake holding ability test procedure published in the Off-Highway Truck Operations and Manual Guides

Recommendation

Caterpillar recommends the replacement of all brake discs that do not meet the guidelines as outlined in Publication SEBF8095 "Guideline For Reusable Parts; Service Brakes for Off-Highway Trucks and Tractors".

NOTE: Although brake disc thickness is found to be in specification and may be used, the passing of the parking brake holding ability test is required to qualify the truck for release into operation. When a wheel group is rebuilt for a non-brake group failure, it should be realized that brake discs not replaced might not allow the component (including the brake group) to reach the next scheduled planned component rebuilds (PCR) due to reduction in brake disc teeth fatigue life or reduction in friction of discs.

Adaptable To: All Off-Highway Trucks, Tractors and Quarry Trucks