Brake Pads & Rotors

[truk4u]

Be sure to check on your pads and rotors, especially the front since they wear down the fastest. In the photo you can see the different size of the inside of the rotor as compared to the outside. The rotors should wear evenly and I probably have a sticking caliper causing the inside to do all the braking. You can see the inside pad at the very top and it's almost gone completely.

I think one of the problems is the calipers don't get greased properly and they miss the fitting.

8270

[Jon Wehrenberg]

A word of caution on greasing that vintage caliper. Too much grease may be worse than none.

There are two fittings inside behind the caliper where the slack adjuster rotates the shaft. I was told and believe if too much grease is applied it prevents the caliper from retracting and the brakes and drag. I give my calipers and the brake shoe pivot points on the drive axle very modest shots of grease. In fact my practice when greasing anything is to only shoot enough grease into any fitting to know grease has flowed. I suspect a lot of the problems folks may be having such as torn grease boots and uneven disc or pad wear may be from too much grease. Of couse not greasing or not enough is not good either.

BTW, this type caliper is not found on later model coaches. I do not know when the caliper style was changed.

[JIM CHALOUPKA]

Be sure to check on your pads and rotors, especially the front since they wear down the fastest. In the photo you can see the different size of the inside of the rotor as compared to the outside. The rotors should wear evenly and I probably have a sticking caliper causing the inside to do all the braking. You can see the inside pad at the very top and it's almost gone completely.

I think one of the problems is the calipers don't get greased properly and they miss the fittings. I just had mine serviced before I brought it home and when I got the front wheels off, one out of two zerks on each side on the calipers were missed and not greased.

8270

Wondering how many miles on those pads?

JIM

[truk4u]

Beats the hell out of me Jim.

[JIM CHALOUPKA]

Tom, I was really wondering the total coach miles and was assuming the pads were original, they do last a very long time and could well be.


A side remark on the pads is that I bought two sets of front pads last fall and found that the lining as supplied on the pair for one rotor was of unequal thickness. Both sets the same dimensions.

For reference one has lining 9/16" thick and the other of the set 7/8" thick.

JIM :)

[truk4u]

Jim,

The miles are 165K and they may be original. My understanding is the Rotor thickness should be equal on both sides. It appears I only have braking on one side for that wheel, the inner pad. The drivers side is the same, lots of wear on the inside, but the pad(s) are not worn as bad. The rotor on the drivers side is scored in one spot and I don't know if that was from a previous pad wearing down and gouging the rotor of if something got between the rotor and pad causing the scoring.

If I have to do the calipers, it's going to be painful.

[Jon Wehrenberg]

I don't see much that has to be done to calipers if they are not functioning properly. They are fully serviceable and if I had to pick one weak point in the design it is where they slide on the pins. That is an area that needs to be smooth, corrosion free, and not have excessive play. It is possible to rebush them if needed.

Other than that disassembly, a good cleaning and inspection for wear or damage on the worm gear should be all that is required to put them back in good shape. Jim is correct in that pad thicknesses vary from inside to outside. That may be due to the fact that as the brakes are applied the inner pad contacts the disc and then pulls the outer pad into contact with the disc. I think (but do not know for sure) what influences uneven wear is how well the caliper slides on the pins. If it slides freely brakes are applied evenly and release easily. If they are not sliding freely the two halves are not sharing equally in the pressure applied to the disc and the brakes will not release freely as intended.

Since Tom is replacing pads he will be pulling at least one pin. By doing that he will see how easily it slides and can determine if he has an issue. Based on what he finds will determine how far he goes in refreshing his brakes.

One thing I am guessing is that his rear caliper on the tag axle will show little or no wear, but that does not mean it should not be checked for the quality of operation.

[flyu2there]

Prepare for some pain! Need to find out of those rotors are WTL or if they can be turned....not to mention that they may be warped. After the wounds on your hands heal up a bit, take those calipers (without taking them apart and covering the inlets, to the bead blaster. Then a nice soak in stoddard solvent would be in order followed by disassembly and internal cleaning. There should be a kit available (o rings or seals) put them back together and install them with AN alodined hardware. Use a good high temp grease on your new (there cheap) jerks and as Jon mentioned not to much. A can of Kroil will come in handy as well, not WD-40. to allow all of those rusted bolts an nuts a chance to be removed....this step also cuts down on the healing time as there will be less hand trauma from the wrench flying off the bolt or nut. That's my 2 cents.......

[JIM CHALOUPKA]

To pull the pins use a slide hammer after loosening the retaining cross bolt nut (after loosening, the cross bolt is pushed in slightly, to release off the brake pin, to enable brake pin removal. failure to release will damage the assembly). The pins are hard chromed for wear and corrosion resistance. Clean them with scotch-brite before replacing. The removable bushings in the calipers may be replaced if there is excessive wear. There are O-rings on the pins and can/should be renewed before assembly. They can be found generically at a good supply house.

Note: This is only one style of caliper used by Prevost.

The photo shows the slide hammer attached to pin. Be gentle in hammering. Be sure to have the caliper supported/retained before pin removal as they are what holds the heavy caliper in place.

JIM:)

[Jon Wehrenberg]

When I pulled my pins I anticipated a problem and had the slide hammer sitting next to me.

After loosening the keeper I was very pleased to find my pins slid freely and were still highly polished and in good shape. I don't anticipate Tom is going to have an issue.

When my rotors (discs) are going to be replaced (when they are at or near the minimum thickness) I will attack the callipers as John describes but in the meantime I'm just watching for signs of uneven wear, cracks in the discs or warping. So far, so good.

[LNDYCHT]

Tom,
I am not surprised that that the inner pad and rotor half wear faster than the outer, when you think of the mass that hangs off the caliper slide pins. It makes sense to me that the inners would wear faster. Under light braking the inner pad is easily forced against the rotor but the force that it takes the outer pad to move also includes the weight of caliper, chamber and brackets.............. well, it makes sense to me.

Its got to be a lot better than then dirt and water cooled drum brakes:)

[MICHAEL BELL]

I hope I can help with the lubrication of brake calipers. On Prevosts manufactured before 1998 they had Meritor brake calipers installed on the steer and tag axles. There are 3 different designs of calipers depending on the year which is Pre 1985, 1985 to 1991 and 1991 to 1998. These calipers had pressure relief valves installed by the grease fittings. Meritor recommends lubrication of the internal actuating components 2 to 4 times during the life of the lining or every six months. These are the steps to lubrication:
1} Turn the adjusting nut on the automatic slack adjuster to move the inboard lining against the rotor (basically tighten the brakes)
2} Plug the pressure relief valve by holding a finger over the poppet (for calipers with grease fittings in the caliper and the camshaft cap, first apply grease to the caliper fitting than the camshaft cap.
3} Apply grease through the grease fitting in the caliper until grease flows out of the camshaft cap.
4} Remove the pressure relief valve from the caliper. Turn the slack adjusting nut in the opposite direction to fully retract the caliper piston and force excessive grease through the pressure relief hole.
5} Install the pressure relief valve and adjust the brakes per brake adjustment procedures.
Note: This procedure forces excessive grease from the caliper. If this is not done than the brakes can drag and reduce the life of the lining.

Most brake problems stem from the lack of lubrication and or use of the vehicle. I personally have never seen any failures from over or not greasing correctly, but have seen many failures as a result of lack of lubrication and or use.
I hope this sheds some light

[Jon Wehrenberg]

Michael certainly has more specific information than I do regarding the proper lube of the calipers of coaches of my vintage. However I feel compelled to point out one thing. Manufacturers of automatic slack adjusters do not want folks adjusting them. All service bulletins on the automatic slack adjusters for coaches of my vintage (1996 chassis) make it abundantly clear we mere mortals do not possess the skills or ability to adjust them and therefore must not.

Having said that I will say that when I replace pads or brake chambers or do any work that requires loosening or tightening the brakes I will adjust them in total defiance of the service instructions. My point is that if you do as Mike suggests make sure you do understand how to loosen and tighten the automatic slack adjusters which are the only kind used with disc brakes.

As an alternative to 6 month service intervals I have had success with lubing the two zerk fittings inboard of the slack adjusters on my disc brakes by giving each fitting a shot of grease. I have a commercial gun pumping grease from a 120 pound drum and I get a noise when the gun gets a shot of grease and that is the limit of what is applied to my fittings every time I lube the coach. The same applies to the drum brake shoe pivot points.