Diagnosing source of contamination leak- Mtbr.com
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  1. #1
    mtbr member
    Join Date
    Mar 2019

    Diagnosing source of contamination leak


    I bought a pair of used SRAM Level TLM brakes and they came with sticky lever pistons. Then I received a warranty replacement set by SRAM and it was mounted for a few days without issues. The rear lever is a bit more spongy and sometimes returns a bit slower, but probably due to routing of the hose, nothing too serious.

    In the middle of a 50km ride through mud, rain, nasty gravel, grass and sleet I heard a horrible squeal going downhill with reduced friction on my front brake. It quickly disappeared, but reappeared again on my way back home in the rain.

    Upon closer inspection, the front rotor had just a little bit of black, oily residue. The stock organic pads where worse. On the backside of the aluminium, a dry circle from the pistons is visible. It is not mere dirt which can be removed. Is this a sign for a slow leak from the caliper pistons or normal? In the caliper body I could see how a bit of paint is missing around the piston in the direction of the braking force which leaves me to believe it is the corrosive DOT fluid. When I inspected the rear one for reference, which does not show troublesome behaviour, I could see the same features. Are these normal symptoms? Do I have to send those warrantied brakes back again? Or is it the contamination from oily puddles, storage in the basement, the front hub or the fork? How can I tell for sure where it comes from as I am not quite convinced about the caliper leak.

  2. #2
    mtbr member
    Reputation: clintj's Avatar
    Join Date
    Nov 2018
    Black filth on the rotors and pads is usually brake dust. Mud, dirt, and just rubbing against the rotors in use grinds down the pads and the ground up material gets deposited on those parts. A quick wipe with a clean, dry, oil free rag will tidy them up.

    Sent from my Pixel 2 using Tapatalk

  3. #3
    mtbr member
    Join Date
    Mar 2019
    You are right about that. I think my mistake to assume it was a leak came from my previous experience with Tektro leaks where I had massive squeal and then always could see an oily film. Whereas here I got squeaky brakes due to mud and rain and overpanicked a bit and mistook the black residue for oil. Even if the piston seals have a leak and this is the reason why some of the paint is chipped off, then it is very, very negligible.

  4. #4
    since 4/10/2009
    Reputation: Harold's Avatar
    Join Date
    Dec 2003
    pretty much any brake is going to make noise under poor conditions like that.

    I did a ride a couple of days ago where I had 15 major stream crossings in about 15mi. Probably half of them were deep enough that I had to get off and walk across. And the streams run hard enough that there were few stones to step across. Needless to say, my bike got wet. And the brakes got loud. I never really got much of an opportunity to drag the brakes for long enough to let them heat up and quiet down, either. Well, I did, but that was early in the ride before all the stream crossings.

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