RV Tech Library - Burnishing Squeeling Brakes

Air brakes require time to properly bed in. New brake shoes come coated with an epoxy resin. Whenever a new coach is delivered, or new shoes are installed on a used coach, these shoes need to be properly broken in or else the resin will glaze over. Once the pads glaze they will vibrate when applied to the drums and the resonating sound shows up as a squeal.

Even if the new linings are not properly broken in, it is still possible to burnish off the resin glaze if it is caught soon enough. If the shoes themselves have been glazed from overheating after being in use a while the burnishing process may or may not help. If the glaze is light it can still be removed but if it is deep into the shoes, they will need to be relined or replaced.

Freightliner has a small section on brake burnishing buried in their Recreational Vehicle Chassis Operators and Maintenance Manual that describes this process. It's hard to find so we'll repeat it here for your convenience.

1. In a safe area, make 10 sharp brake applications or "snubs", slowing the vehicle from 40 to 20 mph using light (approximately 10 to 20 PSI brake pressure.

2. Make 10 stops from 20 MPH using moderate (20 to 30 PSI) brake pressure.

3. Make 2 stops from 20 MPH using hard (full application of air pressure) brake applications.

Note: After the hard brake applications, it is normal to notice a hot brake odor.

4. Next drive the vehicle approximately 5 to 7 miles allowing the brakes to cool, and then come to a stop.

Note: After performing the burnishing procedure, there should be no brake noise and the brakes should have good stopping ability.

5. Inspect each wheel and ensure that there is no excessive end-play.

6. Inspect the brake adjusters and air chambers and ensure that the pushrods have proper and equal stroke.

7. If the brakes pull the vehicle to one side or grab after the burnishing procedure, contact a Freightliner RV dealer for service.

If this helps but doesn't totally eliminate the problem you can always try it again after resting a while. You have nothing to lose by trying. Just be sure to secure any loose items inside the RV to keep them from flying around when you make the sudden stops.

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