6

I have sintered pads and I'm trying as best as I can to diagnose a braking issue. I have Shimano XT M8000 callipers and the rear brake is being something of a pain.

If I leave the bike for about 4 days I lose almost all braking power. As I try and figure this out it would be good to know if there's anything distinct I can see or do to figure out whether ultimately the pads have been compromised.

This brake system uses mineral oil so I'd be looking for tell-tale signs of that or other lubricants. Is road grime a possibility too I wonder?

This issue is driving me crazy and I'm trying to find out if there are any leaks in the system through various methods.

Edit My issue seems to be akin to the one discussed on this thread. http://forums.mtbr.com/brake-time/xt-xtr-brakes-get-squeal-power-loss-after-sitting-idle-6-8-weeks-902792.html

My bike loses braking effectiveness when it sits idle. Quite an odd thing as I'd expect little to no pressure in the system to cause much leaking and surely something should be visible if it is leaking.

Edit 2 to document some fix attempts and diagnosis lines I've been down.

Firstly I manage to get power back by cleaning the pads with IPA and heating them with a gas flame as is mentioned in the comments below.

I've had the bike in the work stand and had a good look for any bubbles around the pots both with a brake bleed block in and with nothing (even pads) in. Bone dry.

I've wiped inside the calliper to see if anywhere is still damp to no avail.

I've visually checked the crimping around the hose and the banjo bolt but there's nothing that indicates build up from sticking to moisture.

Until today I was testing this with just one set of pads. Now there's a chance that my fixes are only good as a temporary measure whilst the bike is being used daily. After sitting maybe some of the contaminants are coming to the surface again. It could also be a build-up of silt from the ride along the canal towpath but I would have expected that to affect me overnight too and not after 3-4 days.

I took the pads out and let them dry for the whole work day one day this week and wiped them with a dry tissue and this did nothing to fix the symptoms.

I changed the rotors front and back although this only affects the rear brake.

I video'd the pots moving with no pads in just in case I could see something when Ina big screen. Not found anything so far. Might need to try it again with a bleed block in for resistance.

I'll add more if I think of anything else I've done.

  • 3
    IPA: India Pale Ale? – rclocher3 Nov 14 '16 at 16:30
  • 1
    Isopropyl alcohol – ojs Nov 14 '16 at 16:41
  • 3
    The beer doesn't last long enough to get near the bike. – Chris Nov 14 '16 at 16:42
  • 2
    When you say the brakes lose all power after 4 days, how do you get the power back? Do you just clean/ burn the pads or do something else? Are you cleaning the rotors also? Pads are cheap so try new ones. But I would suspect a leak or similar and something when you're removing/ installing the pads may account for the few days. – DWGKNZ Nov 14 '16 at 19:23
  • 3
    I often also resort to IPA when repairing bikes. Generally when the kids have run off with the 4mm and/or 5mm hex wrenches and I can't find one (I have 4 sets!). – DWGKNZ Nov 14 '16 at 19:24
1

I lost rear braking on by bike because mineral oil from the rear brake caliper got onto the brake pads. My symptom was a spongy brake handle response and reduced braking power. It seems that the caliper bolt lost a complete seal at the brass washer. I solved this by tightening the caliper bolt and sanding off contaminants from the problem pad and the opposite pad, for security.

I argue that braking is lost most often when air enters the brake lines and when brake fluid comes in contact with the pads. The remedy for the first is to bleed the brakes and to pinpoint the area of leakage. The remedy for the second is to stop the leak and replace or repair the pads.

Your situation may be similar to mine. But it could also be not.

  • 1
    Unfortunately I've had to do this all too often. Trying different pads in the hope that it's just contaminated pads rather than a leak. – Chris Nov 15 '16 at 20:59
  • Dirt is attracted to mineral oil, so if there is a leak, dirt that gathers from riding should accumulate on the path of oil leakage. My leak was obvious because dirt was all over the caliper brass washer seal. – Dan Z Nov 15 '16 at 21:00
  • I was looking for signs last night. All over check and it was bone dry with only dried mud splatters and brake dust. I couldn't see any accumulation around a leak. Banjo bolt is tight as is the bleed port. Nothing along the seam of the 2 parts of the calliper and the pots were bone dry. – Chris Nov 15 '16 at 21:09

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.