Announcement

Collapse
No announcement yet.

Brake discs

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Brake discs

    I checked the disc run-out on my '89 Mini (12-inch wheels) and got a maximum variation on the dial indicator of 0.28 mm. Haynes says the maximum should be 0.15 mm and the Rover manual says 0.05 mm. Am I interpreting run-out correctly? What is the fix? The rotors only have 2,000 miles on them. I sanded the rotors and pads as suggested in the October meeting, but am still getting some shuddering with heavy braking.

  • #2
    Yes that is a lot of runout. They need to be cut down on a lath to straighten.
    "remember, in this country, they drive on the wrong side of the road"
    64 Austin Countryman-???
    '60's Austin mini truck - the chicken truck
    '60 Morris Van - Marvan
    '55 Chevy wagon- the heavy Chevy

    Comment


    • #3
      The question is, why did they warp so soon?

      Don

      Comment


      • #4
        how do you know if the disc is warped or not sitting true on the hub flange? I didn't check the run-out when I installed them.

        Comment


        • #5
          How did you check the run out???.
          "remember, in this country, they drive on the wrong side of the road"
          64 Austin Countryman-???
          '60's Austin mini truck - the chicken truck
          '60 Morris Van - Marvan
          '55 Chevy wagon- the heavy Chevy

          Comment


          • #6
            Is the disc new? It may not have been fully seated when assembled. Theses need further inspection in my opinion.
            "remember, in this country, they drive on the wrong side of the road"
            64 Austin Countryman-???
            '60's Austin mini truck - the chicken truck
            '60 Morris Van - Marvan
            '55 Chevy wagon- the heavy Chevy

            Comment


            • #7
              I mounted a dial gauge on the caliper and with the point near the outer edge of the rotor noted the maximum change in the gauge as I rotated the rotor 360-degrees.

              Comment


              • #8
                As long as everything is still torqued down. That should work. Move the dial indicator inboard, close to the nut. Check run out there to make sure the wheel bearing and axle shaft are running true. If theses were new disc on an old drive flange. Them may have not seated fully when put together. They may need to come back apart to verify correct assembly.
                Wish I had my shop up and running! Hard to diagnose through the wed site.
                "remember, in this country, they drive on the wrong side of the road"
                64 Austin Countryman-???
                '60's Austin mini truck - the chicken truck
                '60 Morris Van - Marvan
                '55 Chevy wagon- the heavy Chevy

                Comment


                • #9
                  The max run-out in my manuals is 0.15mm which is about 0.006". You are seeing a little less than double that or about 0.011" (0.28mm). 0.05mm would be about 0.002" which seems really small for brakes. Volvos and Chevy pickups are 0.004" (0.10mm) for comparison.



                  As you probably know I don't generally believe in discs warping. Even if it's true it's so rare it is the least likely result.


                  I think your measure set up is good. It isolates you from movement in the ball joints but not the wheel bearings (and I'm not sure there's a way to do that). Try finding the highest and the lowest points and mark them. If they're opposite each other on the disc it's likely the problem is in the mounting on the drive flange or the drive flange itself. Do this several times to make sure the high and low points don't move around. Shake the disc really hard between measurements (nothing wrong with hitting it with a rubber hammer).


                  Please report the results. Thank you.


                  Kelley
                  If you can afford the car, you can afford the manual...

                  Comment


                  • #10
                    Yes the max and min points are 180 degrees opposite each other. With the dial gauge I have I couldn't accurately get near the hub to check there. I had Tru-Line do a wheel alignment less than 1,500 miles ago. If there were issues with the hubs would't these have shown up then? (they noted "Light brake warpage" at the time) Next step disassemble and try again?
                    Thanks for your help.

                    Comment


                    • #11
                      When you remove the discs check that the holes don't have a burr raised on the inside and that the drive flanges don't have a burr on the outer portion of the threaded holes. I'm assuming these are 8.4" brakes and I'm assuming that I remember how they go together. You can use a large drill bid to deburr the holes if you don't have a large countersink.


                      Kelley
                      If you can afford the car, you can afford the manual...

                      Comment


                      • #12
                        Took hubs apart again, no burrs seen. ran bit in hole countersinks, ground surfaces with flat stone and cleaned with Dremel wire wheel. After reassembly right hub now 0.008", better than 0.010" but still out of spec. Left hub worse, now 0.018". I took the hub/rotor off again and reinstalled it on a different rotation on the drive shaft, exactly the same result. For some reason the right drive shaft stayed fixed when I removed the hub. The left one was loose and could be slid in and out. I don't think this is significant but just wanted to note it. Something else to try?

                        Comment


                        • #13
                          Minispares says the wheel bearing can spin and wear a very machined groove in the drive flange. My flange definitely has machined grooves in the flange. Time for new flanges? and what else?

                          Comment


                          • #14
                            I've seen this a few times and usually the first sign is loose or loosening wheel bearings, the driveshaft retaining nut becomes loose. The drive flanges will need to be replaced if the groove is very deep. If you can just barely feel the groove or if a fingernail can just grab the groove edge it should be ok. The bad ones I've seen have been pretty deep, less than the thickness of a dime but not by much.



                            Buy the better drive flanges, EN24T steel, if I recall correctly. You will also need to inspect and possibly change the wheel bearings and inspect the hub they mount in.


                            Kelley
                            If you can afford the car, you can afford the manual...

                            Comment


                            • #15
                              Back at it. Before I go any further i just want to confirm that the drive shaft can be loose and able to move in and out in the swivel hub after the driving flange is removed. It is loose on the left wheel but wasn't when I removed the right flange.

                              Comment

                              Working...
                              X