Viewing 13 posts - 1 through 13 (of 13 total)
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    • #3687
      MyPrevost
      Keymaster

      Be sure to check your pads and rotors, especially the front ones, as they tend to wear down the fastest. In the photo, you can see that the inside of the rotor is worn differently compared to the outside. Rotors should wear evenly, so a sticking caliper might be causing the inside to do most of the braking. The inside pad at the very top is almost worn out completely.

      One issue could be that the calipers aren’t getting greased properly, and the fitting might be missed.

      #3689
      MyPrevost
      Keymaster

      A word of caution on greasing vintage calipers: applying too much grease can be worse than applying none.

      There are two fittings behind the caliper where the slack adjuster rotates the shaft. If too much grease is applied, it can prevent the caliper from retracting properly, causing the brakes to drag. I give my calipers and brake shoe pivot points on the drive axle only modest amounts of grease. My practice is to only apply enough grease to ensure that it flows through the fitting. Excessive grease can lead to issues like torn grease boots and uneven disc or pad wear, although insufficient grease is also problematic.

      This type of caliper is not used on later model coaches, and I’m not sure when the style was changed.

      #3690
      MyPrevost
      Keymaster

      Be sure to check your pads and rotors, especially the front ones, as they tend to wear down the fastest. In the photo, you can see that the inside of the rotor is worn differently compared to the outside. Rotors should wear evenly, so a sticking caliper might be causing the inside to do most of the braking. The inside pad at the very top is almost worn out completely.

      One issue could be that the calipers aren’t getting greased properly, and the fitting might be missed.

      Wondering how many miles on those pads?

      JIM

      #3691
      MyPrevost
      Keymaster

      Beats the hell out of me Jim.

      #3692
      MyPrevost
      Keymaster

      Tom, I was curious about the total mileage on the coach and assumed the pads might be original, as they do last a long time.

      Just a side note: when I bought two sets of front pads last fall, I discovered that the lining thickness on one set was uneven. Both sets had the same dimensions, but one had lining that was 9/16″ thick, while the other was 7/8″ thick.

      Jim

      #3693
      MyPrevost
      Keymaster

      Jim,

      With 165K miles, the pads could indeed be original. The rotor thickness should ideally be even on both sides, so the uneven wear you’re seeing might suggest a caliper issue, like sticking. If you’re only getting braking on one side of the wheel, that could definitely be a sign of a problem with the caliper.

      The scoring on the driver’s side rotor could be from previous pad wear or possibly debris getting between the rotor and pad.

      If you end up having to replace or rebuild the calipers, I know it can be quite a job. Good luck with it!

       

      #3694
      MyPrevost
      Keymaster

      I don’t see much that needs to be done to calipers if they’re not functioning properly. They’re fully serviceable, and the main weak point in the design is where they slide on the pins. That area needs to be smooth, corrosion-free, and not have excessive play. Rebushing them is possible if needed.

      Typically, a disassembly, thorough cleaning, and inspection for wear or damage on the worm gear should be enough to get them back in good shape. Jim is right that pad thickness can vary from inside to outside. This might be because as the brakes are applied, the inner pad contacts the disc first, which then pulls the outer pad into contact. Uneven wear can often be attributed to how well the caliper slides on the pins. When the caliper slides freely, the brakes apply and release evenly. If it doesn’t slide freely, the pressure on the disc isn’t distributed evenly, and the brakes won’t release properly.

      Since Tom is replacing the pads, he’ll need to pull at least one pin. This will let him see how easily it slides and help him determine if there’s an issue. Based on what he finds, he can decide how far to go in refreshing his brakes.

      It’s also worth checking the rear caliper on the tag axle, even if it shows little wear, to ensure it’s operating properly.

      #3695
      MyPrevost
      Keymaster

      Prepare for some pain! First, find out if those rotors are WTL (Wet Turnable) or if they can be turned. They might also be warped. After your hands heal a bit, take the calipers (without disassembling them and covering the inlets) to a bead blaster. Soak them in Stoddard solvent, then disassemble and clean them internally. There should be a kit available with o-rings or seals to reassemble them. Install them with alodined hardware and use high-temp grease on your new (they’re cheap) jerks.

      As Jon mentioned, don’t over-grease. A can of Kroil will be useful for rusted bolts and nuts, as it’s better than WD-40. This will help with removing rusted parts and reduce hand trauma from wrench slips. That’s my two cents…

      #3696
      MyPrevost
      Keymaster

      To pull the pins, use a slide hammer after loosening the retaining cross bolt nut. Once loosened, the cross bolt will push in slightly to release the brake pin, making removal possible. Failure to do this properly can damage the assembly. The pins are hard-chromed for wear and corrosion resistance, so clean them with Scotch-Brite before replacing. If there’s excessive wear, the removable bushings in the calipers may need replacing. Renew the O-rings on the pins before reassembly; they can be found generically at a good supply house.

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

      The photo shows the slide hammer attached to the pin. Be gentle when hammering. Ensure the caliper is supported and retained before pin removal, as it holds the heavy caliper in place.

      JIM

      #3697
      MyPrevost
      Keymaster

      When I pulled my pins, I had the slide hammer ready, anticipating a problem. However, I was pleased to find that my pins slid freely and were still highly polished and in good shape. I don’t anticipate Tom will have an issue.

      When my rotors (discs) need replacing (when they are at or near the minimum thickness), I will tackle the calipers as John describes. In the meantime, I’m just keeping an eye out for signs of uneven wear, cracks in the discs, or warping. So far, so good.

      #3698
      MyPrevost
      Keymaster

      Tom,

      I’m not surprised that the inner pad and rotor wear faster than the outer ones. Given the mass hanging off the caliper slide pins, it makes sense that the inner components would experience more wear. Under light braking, the inner pad is pushed against the rotor more easily, while the outer pad has to contend with the additional weight of the caliper, chamber, and brackets. This explains the uneven wear.

      It’s definitely an improvement over dirt and water-cooled drum brakes!

      #3699
      MyPrevost
      Keymaster

      I hope this helps with brake caliper lubrication. For Prevosts made before 1998, which had Meritor brake calipers on the steer and tag axles, there are three designs based on the year: Pre-1985, 1985 to 1991, and 1991 to 1998. These calipers included pressure relief valves at the grease fittings. Meritor recommends lubricating the internal actuating components 2 to 4 times during the life of the lining, or every six months. Here’s how to do it:

      1. Adjust the Brakes: Turn the adjusting nut on the automatic slack adjuster to move the inboard lining against the rotor (tighten the brakes).

      2. Plug the Pressure Relief Valve: Hold a finger over the poppet to plug the valve. For calipers with grease fittings on the caliper and camshaft cap, first apply grease to the caliper fitting, then to the camshaft cap.

      3. Apply Grease: Pump grease through the caliper fitting until it flows out of the camshaft cap.

      4. Remove the Pressure Relief Valve: Take out the valve and turn the slack adjusting nut in the opposite direction to fully retract the caliper piston, forcing excess grease through the pressure relief hole.

      5. Reinstall the Pressure Relief Valve: Put the valve back and adjust the brakes as per the brake adjustment procedures.

      Note: This process removes excess grease from the caliper. Failing to do so can lead to brake drag and reduced lining life.

      Most brake issues are due to lack of lubrication or use. While I haven’t seen failures from over-lubrication or incorrect lubrication, many issues arise from inadequate lubrication or infrequent use.

      I hope this clarifies things!

      #3700
      MyPrevost
      Keymaster

      Michael has more specific information for calipers of my coach’s vintage, but I feel compelled to point out one thing. Manufacturers of automatic slack adjusters generally advise against manual adjustments. Service bulletins for coaches of my vintage (1996 chassis) clearly state that only professionals should handle adjustments.

      That said, when I replace pads or brake chambers, or perform any work requiring brake adjustments, I do adjust them myself, despite the service instructions. If you follow Mike’s suggestions, ensure you understand how to properly loosen and tighten the automatic slack adjusters, which are the only type used with disc brakes.

      As an alternative to the recommended 6-month intervals, I’ve found success by giving each zerk fitting inboard of the slack adjusters a shot of grease. I use a commercial grease gun from a 120-pound drum, applying just enough grease to hear the noise of the gun, which indicates the fitting is properly lubricated. This also applies to the drum brake shoe pivot points.

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