C2 Rear Run-out measurment - NCRS Discussion Boards

C2 Rear Run-out measurment

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  • Dan Pepper

    C2 Rear Run-out measurment

    Oh Wise Ones...

    Following the advice of the Forum's best and brightest (and I mean that with utmost sincerity), I've been working to rid the sponge from my 66's brake system. The advice was to bench bleed the MC, and check the run out on all 4 rotors.

    I removed the J50 MC, and proceeded to bench bleed it. I think this may fix the problem since the first compression of the MC piston produced a burble instead of a squirt. Now both ports produce a good squirt - the front port a noticeably larger volume squirt than the rear, but I figure that's the way it is by design (right?).

    Now onto run-out. I set-up a dial indicator to check the front rotors; these checked-out at between .004 - .007. Pretty close to spec. Here's the rub; on checking the rear, I was having a hard time getting an accurate reading. The effort required to turn the wheels (yes, it was in neutral) made the needle wander quite a bit. Furthermore, the U-joints would bind just a bit, causing the axel to raise/lower a few thousands, thereby throwing the dial way off. I put a jack under the spring to load the suspension a bit, but the erroneous movement was still noticeable. How should I set-up the car to get an accurate measurement?

    As always, thanks for the education.
  • Gene M.
    Extremely Frequent Poster
    • April 1, 1985
    • 4232

    #2
    Re: C2 Rear Run-out measurment

    you need to support the spindle up so the u-joints don't bind and you can turn the disc. Try securing the dial indicator to the spindle trail arm. keep the spindle bearing clearance (couple thou) biased (in or out)so you don't read this in the disc runout.

    Comment

    • Dan Pepper

      #3
      Re: C2 Rear Run-out measurment

      Of couse, makes perfect sense. My dial indicator doesn't have mounting pariphinalia, so I had it clapmed in a vise mounted on a short section of 6x12 wood beam. Althought it was very stationary, it didn't "go with the flow" when binding occured. I'll find a way to mount the indicator to the unit.

      Also, thanks for the reminder RE the spec'd couple thou play.

      Thanks, Gene.

      Comment

      • John H.
        Beyond Control Poster
        • December 1, 1997
        • 16513

        #4
        Re: C2 Rear Run-out measurment

        Dan -

        A magnetic base is really handy for measurements like this - Harbor Freight has pretty inexpensive ones; not Starrett stuff, but a magnet is a magnet

        Comment

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