Class A DP air brakes screech when applied

[Chiefly1]

I have a high pitch squill from the front when I hit the brakes that just started. As I only have 40K I wouldn't think I have worn out brakes but I'm the second owner in this 06 Revolution so I have no idea how it was driven before me. I do not have the equipment to support it or tear it apart so I'll need to take it somewhere. The RV does not pull to any side. So, need your thoughts and recommendations.


Bill & Christine
40 ft Revolution LE Diesel Pusher & Honda Fit Sport
Sent from my iPad using iRV2 - RV Forum

[SteveLevin]

Before I'd assume that the brakes are worn out, there's a good chance that -- especially if you yourself are very light on the brakes -- that they are just glazed. It's something that can happen when you don't apply the brakes heavily enough. (I'll leave it to others to explain the whole technical part of it).

To test that theory, just take your motorhome out (and be cautious, etc, of course, just in case it really is the brakes, although that usually ends up being a metallic grinding sound), and firmly apply the brakes while driving (and try to avoid coming to a complete stop between applications of the brake pedal). Do that a number of times while driving around and the odds are the squeal will go away.

Steve

[jacwjames]

Mine will do that when I first start to use it after it has been sitting. One advantage that I have is that I have to back down my driveway applying the brakes to control speed. They usually screech all the way down the driveway. The subdivision that I live in has a steep hill that I have to descend to get to the main roads. By the time I do all of this my brakes seem to calm down and I don't really hear them after that.

I have ~102K miles on my coach and my brake pads are only 1/3 wore out. There are bevels on each of the pads which help judge how much they are wore. I have put ~50K on my coach since purchasing it in late 2008, I can't tell that the pads have wore much at all.

Also, there was a recent post on air brakes, fairly lengthy but one of the tips that I gained out of it was how to help the slack adjusters adjust. To do this, while parked, firmly press the brake pedal 10 times. This will make sure the adjuster is working and should adjust to close to the recommended tolerance.

[Fred Cooper]

After sitting a while (high humidity), my brakes will do that also. It is simply moisture in the brake shoes. Driving a block or two with the brakes lightly applied will dry them out and they are then quiet for the remainder of the trip.

Fred

[Hooligan]

As Steve mentioned above, Freightliner has a procedure for "burnishing" the brakes. It is described here: RV Tech Library - Burnishing Squeeling Brakes

[dons2346]

At 40K you have not worn out the brakes. Most likely, if you really use the brakes hard a few times the squeal will go away. Drums get a light coat of rust on them and will do that until you get the rust off. Mine will squeal after sitting for a couple of days but a hard stop or two it quits.

[the_vfox]

Ours will squeal if we sit a while. A couple applications will make the noise go away. Unless you use the breaks a lot when driving, your shoes should be very good at 40K.

[H. Miller]

Recent wheel maint.? We had bearings repacked with a resultant loud squeal at brake application. 40 miles home and it didn't quit. Called maint. facility and they said contaminates (dust/dirt) had probably gotten on the shoes or drums and to use a garden hose from the underside and wash them down. Now 50,000 more miles and not a peep...

Coming on 100,000 miles and still have at least 50% of brake lining remaining.

[YC1]

Ditto on squealing after sitting. It goes away after I annoy all the campground folks while leaving.

[RayBH]

"Also, there was a recent post on air brakes, fairly lengthy but one of the tips that I gained out of it was how to help the slack adjusters adjust. To do this, while parked, firmly press the brake pedal 10 times. This will make sure the adjuster is working and should adjust to close to the recommended tolerance."[/QUOTE]

I am wondering if there is not a warning that should come with the above mentioned procedure. The procedure says "while parked" which implies that the parking brake will be on. The following is an excerpt from the manual to obtain an air brakes certification where I live :

"Driver alert - compounding of brakes.
Always be sure that the spring parking brakes are released before making heavy service brake applications, like during a pre-trip inspection.

When spring parking brakes are applied, there's up to 2,000 lbs of force applied to all of the brake components. If a heavy service brake application is made, the force of the air application is added to the spring force. This could add a further 3,000 lbs for a total of 5,000 lbs. This adding together of the two forces, known as compounding, can damage slack adjusters, s-cams, brake chamber mounting bolts, brake shoe rollers, shoes and brake drums.

Note that lighter brake applications of less than 30 to 40 p.s.i., to prevent a vehicle from rolling while the spring brakes are being released or applied, aren't harmful."

The course instructor made a big issue of this point, so I felt it worth passing along in the context of this thread.

[Chiefly1]

Great suggestions that I'll try out Monday when I get back to our RV and I'll let you know what happens.


Bill & Christine
40 ft Revolution LE Diesel Pusher & Honda Fit Sport
Sent from my iPad using iRV2 - RV Forum

[Chiefly1]

Thanks for the advice! Finally got back to our rig and to update everyone the flushing with water worked... I think. I used the water suggestion and then test drove it but as I was picking up speed the car in front of me lost a wheel. So the first application of the brakes was a panic stop. No damage and no sound from the brakes equals a happy camper!


Bill & Christine
40 ft Revolution LE Diesel Pusher & Honda Fit Sport
Sent from my iPad using iRV2 - RV Forum