[Archived]

This lack of any notice or response from Prevost is not good. If this problem is as common as the posts say everyone should contact NHSTA and file a vehicle safety complaint. Their number is 888-327-4236 and they will want your vin.

it doesn’t make any sense to keep replacing pads after a few miles when if enough people call and get a recall going we can all get our brakes fixed for free.

[AL]

Zeeman, this problem is not likely going to be an issue with your brakes which are all drum brakes, but your comment about people affected reporting this is valid because from the photos above it is clear the brakes are going to far less effective than they should be, and with some of the cracking and other signs they are coming apart it is clear a panic stop could cause brake failure.

[Archived]

Prevost has not responded. I have emailed photos to the Bendix Tech Team since Knorr-Bremse owns Bendix to see if the braking system experts can offer an opinion on the cause and way to prevent the issue.

I will stay on this and at this point I am disappointed by the lack of response from Prevost.

[steve]

Are these a specific pad built for Prevost or a over the counter, common pad that everybody is having trouble with. I’ve got drums so I don’t have a dog in this hunt.

[Archived]

I doubt if these are “over the counter” pads. First, from what I can determine all of the pads that have crumbled or disintegrated were original equipment. But if pads were replaced on our coaches it is likely they were supplied by Prevost because it is almost impossible to go to a truck or bus parts store and have a guy with a computer find a listing for brake pads for Prevost.

They can look up widely used parts for Freightliner or Kenworth, but their listings of parts for buses are sadly lacking.

[Dick]

Unless and until I can get some answers from experts about cause and prevention I am trying to research this issue. There are countless forums but few of the opinions expressed seem to be little more than opinions. However there are some possible causes listed by companies or experts.

https://www.juridparts.us/technical-support/brake-trouble-tracers/brake-pad-issues.html#symptom=12

Here are some questions based on what I have learned so far.

Has anyone with the disintegrated pads measured the hub or wheel temps on the coach to see if there was a dragging caliper?

What axle or axles have the disintegration shown?

Of those coaches with disintegration has the coach been unused for long periods and if so has the storage been in high humidity conditions?

Are any of the coaches with this problem used and kept in dry conditions such as the desert Southwest?

[Per]

As I continue to dig into this situation I got a response to my questions that not only made a lot of sense, but seems viable.

Can any of you who have had this situation determine if the coach was stationary for a long time period, and if the conditions were with high humidity that could cause rust and the pads to stick to the discs?

Does anyone know if the metallic composition of the Knorr-Bremse pads is greater than the Meritor pads not exhibiting the problem?

Anyone?

[Dick]

Jon you bring up something that reminds me a long time ago Beechcraft told pilots to quit washing the planes as much as we did and especially the wheels and brakes due to corrosion. As much as most of us wash our coaches, and you bringing up moisture you might be on to something.

[Per]

I have been contacted by Prevost and now rather than speculate I am hoping with their resources they can help us determine the cause, prevention, how to inspect for the problem, etc.

[Roy]

Jon, when they changed the front tires they found the front brake pads were disintegrating as described and shown in pictures. They took the hub apart to see if there was any damaging heat from the tire blow-out, but did not find any. The coach did sit for about two years before we bought it. This was in New Braunfels, northeast of San Antonio–fairly humid. The dealer bought it for him and his wife, but then she passed, and he had a hard time getting rid of it.

[Archived]

I hope anyone that has had issues with disintegrating pads would post here, pictures if possible, age of coach, miles and if you know if they are original.

The gentleman at Prevost that I have communicated with has access to read these posts and the more information we can provide the better it will be for him.

[Bernie]

My 2001 Liberty XLII with Knorr-Bremse had about 170K on it when I bought in Dec 2016. I have put about 20K on it since purchase. I am third, maybe 4th owner, prior owner was from Dallas area, not sure of one before that, but think maybe first owner was from around TN name was Westmoreland.

I have stored it indoors most of the time owned, driven it all over US and far western Canada. I have never had it in snow or salt, do not know about prior owners but from undercarriage condition don’t think they ever did.

I replaced all brake chambers and hose over this past winter. While doing the job I saw that all brake linings looked basically new, not rusted, deteriorated, or even worn to any visible extent compared to the new set I purchased to have on hand in case of a caliper lock up or whatever. Do not know if the pads were original but the brake chambers and hoses were original. I suspect the pads were original too as all the associated hardware had no signs of some gorilla working on it prior to me. The rotors also looked basically new with minimal wear. The accordion rubber seal on caliper pins were deteriorated and a couple missing, I have since bought replacements but have yet to put them on.

I do note that my bus has a trans retarder and I use that for almost all of my stopping. Use the brakes only for the last few bus lengths when coming to a complete stop. I learned to take large downgrades at reasonable speeds so that with retarder use and downgearing, I can keep trans temp below 230.

For example with 4th gear and 4th or 5th retarder notch can go down the mountains from Flagstaff to Phoenix without any brake application. Memory says maybe 45mph for the steepest portions.

I had observed a few instances in the past that during in town driving when I did need to stop quickly from low speed and used the brakes it did not seem to stop as well as I would like. I surmised that from my (and maybe former owners) “disuse” of the brakes for stopping in general and their only getting light use they “glazed”. So after replacing the brake chambers and hoses, I took it out for a good run and did the specified procedure for burnishing new brake pads ( I did not put on new pads, this was with the existing maybe “glazed” pads.) Essentially doing a series of fairly rapid slowdowns from 60mph with plenty of time for cooling in between. It was amazing the difference in stopping afterwards.

So, now on each trip, I make it a point to make a few of my exit ramp stops with moderately firm braking to keep from glazing pads again.

Regarding the deteriorating pads, I don’t know if there is an underlying friction material defect causing disintegration from moisture, and kudos to Jon for working to see if some pattern can be identified. If not, I do know in my years as a service rep with Ford I saw many examples of heat damage to brakes on light and medium duty work trucks in the mountains of western PA that looked just like the pictures.

I suspect some of our prior owners of the involved coaches might have fried the brake pads at some (or many) point. It only takes one time above the critical temperature for the bonding agents in friction material to be irreversibly damaged.

I think a lot of “non gearhead” folks (no slight here, we all have our own talents and aptitudes) underestimate how hot you can get brakes on vehicles such as ours going down long steep grades. Its is a fairly simple (conceptually – the math and measurement is very complex) physics problem of energy dissipation, we are turning the potential energy of a large mass at some elevation into heat as we descend. If you can not dissipate that heat at a RATE faster than you are generating it you fry your brake pads, or in the case of trans retarder your transmission fluid.

Rate being the key word here, if you slow down your speed during the descent, it takes longer to get down the mountain and you have more time to dissipate the same amount of heat into the atmosphere and the brakes or trans fluid don’t get as hot at any given time, even though they ultimately dissipate the same amount of energy.

[Art]

“So after replacing the brake chambers and hoses, I took it out for a good run and did the specified procedure for burnishing new brake pads ( I did not put on new pads, this was with the existing maybe “glazed” pads.) Essentially doing a series of fairly rapid stops from 60mph with plenty of time for cooling in between. It was amazing the difference in stopping afterwards.“

Ideally, you don’t come to a complete stop under hard braking due to the uneven heating of the rotors or drums at the very end. We follow a burnish procedure outlined in FMVSS 121, 40 to 20 mph. I have seen braking distances decrease by as much as 50% after a burnish. It creates full contact and transfers some friction material to the drum/rotor.

[Roy]

You are right. It was not complete stops, rather slow downs to your cited speeds. Thanks for the correction.

[Dick]

HUH. Very interesting. In racing we call this bedding in brakes. Often we can buy pads and rotors that are already bedded. If not, we “bed the brake” on the track in an open session, then park on pit road until everything cools off (engine off, car in gear, foot off brake, after coasting to a stop; tough to do with a Prevost).

So the idea is to do this procedure but NOT come to a complete stop so the brakes have to be held. Keep moving, keep rolling. Will try it and report back.

A friend who is not a gearhead and not to mechanically inclined bought a Dodge van converted into a very basic RV. Probably a 3/4 ton, maybe a half ton. He told me he and wife went to Yellowstone last year. She was driving and came to a long, steep hill down a mountain that had a sign at the top something like “Steep Grade. Trucks use lower gear.” They didn’t think they were a truck and were afraid of damaging the engine in a low gear. So down the hill they went. She used the service brakes to keep from going too fast. Near the bottom of the hill the brake pedal went to the floor. Fortunately they found a place they could pull off and get stopped. No cell service at the bottom of the hill in the valley. So they sat. (I suspect they opened the hood and looked into the engine compartment, but don’t know for sure. Doesn’t everyone do that?). After a while “the pedal worked again”. So they went out of the park to a small town and found a car repair shop. Owner said this happens all the time with Yellowstone visitors. I think he said the bill was $1,100 or $2,100, can’t remember (was biting my tongue too hard). I asked if they replaced rotors, pads, calipers, and fluid. He wasn’t sure … “guy said he had to replace everything”. My friend was just baffled that the brakes could be ruined on a hill like that and end up with no pedal. I told him that if they had downshifted like the sign said and kept the RPMs below the yellow or red line they wouldn’t have ruined the engine and the brakes would have fine. I don’t know if the brakes were ruined and the car repair guy bambuzzled him or not. The van was older, probably had original brakes, probably not too much wrong with all new brakes in front.

I think there here is a good lesson in this tread for readers who are new to heavy vehicles and the technology and science of the breaking systems. It’s easy to overheat the brakes on our coaches if we’re not careful!