Do I have a leak in my brake system? - NCRS Discussion Boards

Do I have a leak in my brake system?

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  • Larry T.
    Expired
    • May 15, 2007
    • 404

    Do I have a leak in my brake system?

    About four months ago I installed a set of four rebuilt stainless sleeved, o-ring sealed calipers from Lonestar on my car. I refilled with DOT 5 silicone brake fluid, bled everything and it has worked great. Doing my normal follow up on the brake job I decided to check my non power brake master cylinder to be sure I was not losing any fluid. To my surprise the level showed 3/4 to 1" lower than where I had filled it to.

    I checked all of the fittings, bleeders, brake lines, etc., I even pulled the master cylinder and pulled the boot on the back just to be sure it was not leaking out of the back. I can find no evidence of a leak at all. Is it possible that it was a matter of small air bubbles in the DOT 5 having worked their way out of the fluid, or am I missing the leak? It never felt spongy to me. If it is leaking from one of the pistons I assume I would see some visual evidence. The brakes feel as good as ever.
  • Joe L.
    Beyond Control Poster
    • February 1, 1988
    • 43211

    #2
    Re: Do I have a leak in my brake system?

    Originally posted by Larry Tape (47364)
    About four months ago I installed a set of four rebuilt stainless sleeved, o-ring sealed calipers from Lonestar on my car. I refilled with DOT 5 silicone brake fluid, bled everything and it has worked great. Doing my normal follow up on the brake job I decided to check my non power brake master cylinder to be sure I was not losing any fluid. To my surprise the level showed 3/4 to 1" lower than where I had filled it to.

    I checked all of the fittings, bleeders, brake lines, etc., I even pulled the master cylinder and pulled the boot on the back just to be sure it was not leaking out of the back. I can find no evidence of a leak at all. Is it possible that it was a matter of small air bubbles in the DOT 5 having worked their way out of the fluid, or am I missing the leak? It never felt spongy to me. If it is leaking from one of the pistons I assume I would see some visual evidence. The brakes feel as good as ever.
    Larry------


    If there's a leak, it will usually be quite obvious, especially with silicone-based fluid which is not as volatile as glycol-ester-based fluid. I'd refill the master cylinder to the correct level and then check it again later.
    In Appreciation of John Hinckley

    Comment

    • Kenneth T.
      Very Frequent User
      • March 23, 2008
      • 631

      #3
      Re: Do I have a leak in my brake system?

      Larry,

      I have found that air bubbles can cling to the nooks and crannies of the cast caliper,and creep out later. I used to tap them with a rubber mallet when bleeding to chase them out.

      If you have a firm pedal and no apparent leaks or seepage, just be vigilant...check the level again several times, but it should be stable at this time.

      Ken

      Comment

      • Edward J.
        Extremely Frequent Poster
        • September 15, 2008
        • 6940

        #4
        Re: Do I have a leak in my brake system?

        Larry, I have seen the master cylinder cap gasket leak fluid down the rear of the master.Also take a look at the inner part of the wheels to see if theres any fluid dripping on the wheels as the car sits over night or for a few days.
        New England chapter member, 63 Convert. 327/340- Chapter/Regional/national Top Flight, 72 coupe- chapter and regional Top Flight.

        Comment

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