Brake noise

[gmcbuffalo]

On my 91 XL chassis I get a loud bang if a hit them hard like in a panic stop. Only on the right side. I have had it checked by Prevost ML and by Southern Oregon Diesel and both told me no problems. But why the noise and the feeling something is breaking looose?
GregM

[Jon Wehrenberg]

Greg,

Did they check your bushings? When you are making a hard stop the steer and tag axles are trying to rotate and move rearward. The only thing that keeps them from doing that is the radius rods that position the axles. Unless bushings have been changed sometime during the life of the coach they may be allowing movement that would otherwise be snubbed.

I think the same could be true of the drive axle, but in that case the axle cradle is supported at each end with air bags.

[Joe Cannarozzi]

Greg is it on the steer axle? Do you have a 4 shock front end?

[dreamchasers]

I can equate to the loud bang noise when applying moderate breaking pressure. When I owned an American Eagle, built on a Spartan chassis, I had loud banging noise and a sharp pull to the right occur when I applied the brakes with moderate pressure. The banging was coming from the right front brake assembly. After many months of in and out of various shops, with all saying 'no problem', I took the coach to the
Spartan factory in Michigan. With a breif description of the problem, these guys went right to the problem and in quick order it was repaired.

The problem centered around the 'S' cam that extends into the brake housing and activates the brakes when twisted by the braking air chambers. The 'S' cam rides on two rollers attached to each brake shoe. When the brakes are applied, the shaft connected to the 'S' cam twists because of brake air chambers, thus twisting the 'S' cam and pushing out on the brake shoes. The brake shoes came in contact with the brake drum, thus slowing the vehicle. The issue was the rollers on the end of the brake shoes that rode on the 'S' cam were seized from non or low usage. When the brakes were applied the rollers would skip on the 'S' cam instead of rolling and applying smooth braking pressure.


To resolve the problem, Spartan removed the brake shoes, freed up the seizes rollers on the end of the brake shoes. They lubricated all with a light coating of 'never seize' and all was well. It took a half dozen attempted repairs at shops all over Fort Worth of failed repairs for me to drive to Michigan for factory repairs.

I hope someone that is familiar with the Prevost braking system jumps in to help, because the experience I am relating is with the Spartan chassis braking system.

Hope this helps.

Hector

[Joe Cannarozzi]

Good post Hector I too have been experiancing that and never tore that corner down to that point. It has been bugging the hell out of me.

It only happens when I stab the brake pedal, usually when jocking around.

I also noticed on our 40 my front air bags are much taller than those Prevo sent us for Warrens 40. I have been experiancing breaking eyelets off the shock ends. I am now thinking the front air bags will raise the front end in level-low further than the shocks will extend.

Again great post Hector:)

[dreamchasers]

Joe,

Thanks for the comment.

Hector

[gmcbuffalo]

Thanks guy for the input. I will check the bushing or should I say replace them because I am sure they are originals. Yes, the problem is on the steer axle and I only have one shock on each wheel. I notice that there is holes for a second. Should I be adding a second shock to each side. Hector I will check the rollers for free movement.
Thanks
Greg

[Jon Wehrenberg]

Greg,

At one time the second set of shocks were added. As I recall it was to deal with converted coaches that had excessive weight on the front end that were experiencing rebound when going over bumps. If you have not had any bottoming of the suspension when going over bumps or undulations in the road I suspect you will not need that second set.

I think Hector's opinion of the problem may be on target and the simplest and fastest way to confirm that is to lube up the rollers and the S cam and go try a hard stop. They are likely to be easily accessed just by turning the front wheels fully left or right and using a mirror to see them.

[dalej]

Greg, if you have a smooth ride while driving thru dips and crossing bridges you don't need to add the other two shocks. They are only needed if your bus has a front weight heavier then the two shocks can handle. It you can think of what a bus would ride like without shocks, you wouldn't stop moving after hitting a dip, the bus would be going up and down almost all the time.

Our bus has 4 shocks on the front and I'm going to remove two of them now after 10 years and see if I get a better ride. My front weighs in at 12,800, road ready, i.e. full of fuel and water.

[Joe Cannarozzi]

I am going to pull the brake drum remove the return springs on the shoes and back off the slack adjuster.

That way all tension on that s-cam is gone and I can grab it and see if I can shake it around.

[Jon Wehrenberg]

Joe, If the slack adjusters and the rod going to the S cam have been lubed that is likely rotating freely and probably doesn't have much wear.

But the rollers on the end of the shoes riding on the S cam are dry as is the S cam. If they aren't rolling freely, either in the end of the shoes or on the cam that is the area most likely to be the culprit. At least that's the way I read Hector's post.

[gmcbuffalo]

Not being setup to remove wheels at the house I hope I can get to them b y turning the wheels L and R.

I have bottomed out once or twice. My front axle is heavier than I like with both the generator and 8 4D's and three 3000 Watt inverter in the second bay across. I'll watch it on our next trip.
Thanks GregM

[dalej]

Greg,

What does you steer axle weigh? I have put on 100,000+ on our bus and have never bottomed out. Did you have less then normal pressure in the air bags? I can't imagine your bus hitting bottom. I would think that would pop the air bags.

[gmcbuffalo]

Question how do you check the air pressure in the bags? I am close to 14K on the front axle.
GregM

[Jon Wehrenberg]

While it is possible to check air bag pressure by adding a bunch of fittings and an air pressure gauge none of us has any ability to influence or alter the air bag inflation pressures.

The ride height valves are a mechanical device which admits air or exhausts air from the air bags depending on the position of the lever arm. When the ride height valve lever arm is positioned so air will flow into the air bag the increase in air pressure inside the air bag raises the coach body until the arm is in the neutral position. At that location air neither enters or exhausts from the air bag.

Our ride heights are determined solely by the amount of air pressure in each air bag, but only to the extent that the pressure increases or decreases the height of the air bag to move the arm to the neutral position.

At one time in the early 90s some converters were exceeding the Prevost front axle weight limits, and as a result the air bags that were installed were not large enough to raise the front of the bus. Remember that the bus is raised by the air pressure inside the air bag, and to increase the lifting ability the air bag needs an increase in diameter. More surface area equals more lift at the same pressure. As a result Prevost retro fitted some coaches with larger air bags.

This has nothing to do with brake noise.

[gmcbuffalo]

DaleJ
Did you remove on set of shocks and if so did it change the ride?
GregM

[dalej]

Greg,

No, I haven't done anything to the bus, It's been sitting since October. I will pull two shocks off the front and add the enviro-cool filter to the cooling system before we leave the end of January. I will let you know how it rides.

[Yankee802]

Joe, gmc, did you guys check the rollers? Any updates to this? I just experienced this when doing my montly run, had to stop hard for a light that changed sooner than expected, kinda freaked me out. I would love to know if it's this or not.

Geoff

[Jon Wehrenberg]

It probably is. An actively driven vehicle is constantly exercising the rollers that ride on the "S" cam. That keeps the roller and the "axle" for the roller free of corrosion and binding. There are no bearings in there, nor is there any provision for lubing beyond what Hector described. When you hit the brakes hard after periods of inactivity I think the bang is the result of exactly what Hector described. On a front axle, turning the wheel gives limited access to the "S" cam and the pair of rollers riding on them. You likely need a small mirror and something to reach into the rollers. The quick, but not necessarily good way to lube them might be to give a shot of oil to the roller axles, but at best it is a bandaid. The whole assembly of parts needs to be wire brushed clean and lubed as described. If you want a quick answer, daub some grease on the rollers and "S" cam so they slide. The roller will not turn, which it should, but the bang should go away for a while. That is NOT a fix.

[gmcbuffalo]

Doesn't look like we are going to make our trip South to warm weather. So the bus is under it's cover. Too cold here in Oregon to crawl around under it outside.
GregM