Rim brakes and alloy rims

Discussion in 'General Questions' started by Happy Valley, Jun 8, 2009.

  1. Happy Valley

    Happy Valley Active Member

    There is a condition known as galling on alloy rims when use and heat cause the alloy material to gather and then embed into the rim brake pad material.

    I've had this happen to two different MBs so far this year but never had it happen on bicycles before. These are decent brake pads, well up from the wear line. If you don't catch it early the embedded metal chips in the pads will seriously cut into a rim to near ruinous condition. I'm trying sanding the rim brake surface out with ascending grits of emery paper and finish with an automotive body work scotchbrite pad.

    Wondering if anyone else has had to deal with this? I'm thinking it's from the higher MB braking speeds.

  2. mlcorson

    mlcorson Member

    Hello Happy:
    On my bike, I see some galling from the pad depositing material onto the rim, but not the other way around. Would you please share some pictures of this?
  3. Happy Valley

    Happy Valley Active Member

    Hey Mike
    I'm between cameras so can't do a pic just now, and I sanded the rims out pretty much.

    This seems to happen on one side of a rim. It happened on one bike with cantilevers and one with linear pull V brakes. These are both decent quality double wall rims and kind of why it tics me off. I notice the aftermath which looks like snags in the metal and scratched grooving trailing away in the direction of wheel rotation.

    One day I was walking one of the bikes from the garage and I applied the brakes down a little slope and heard a scratching sound so I unhooked the brake arms and looked at the pads. I dug out bits of alloy embedded in the pad material but went ahead and swapped out new pads.

    I was just curious if anyone else was having this happen?
  4. Warner

    Warner Member

    My rim brakes squeak LIKE CRAZY. I had a guy in a car yell out to me last night "Nice Brakes" when I was coming to a stop. They ARE incredibly annoying...so I couldn't disagree. I'm not sure how to quiet them though....any ideas? I'd LOVE to have disc brakes, but I'm not sure what's involved in converting to them....anyone know?

    Thanks and sorry for the thread hijack,

  5. Happy Valley

    Happy Valley Active Member

    Hey Warner
    Squealing in rim brakes is usually caused from the pads not having proper toe-in adjustment.

    You can remedy this with an overall adjustment, make sure each pad is where you want it on the circumference of the rim. Then, slightly angle in by about 1/16'" the leading edge of the each pad, or the toe, to touch the rim first.

    Doing this is also a good time to inspect the pads, clean them if they are grungy with a little alcohol or if they show glazing clean them up with a little fine grit sandpaper.
  6. SirJakesus

    SirJakesus Guest

    Sometimes squealing is caused by just cheap brakes. If you adjust them a million times, a million different ways and change out the pads to high quality ones and you still get squeal its time to get new brakes. This is fairly common with low quality dept store brakes but I've never had the issue with decent rim brakes except for wet weather.

    As far as the galling issue, I've never experienced this problem but I'll be sure to look out for it in the future. My wheels with rim brakes definitely show wear but I've never had a problem with the rim being compromised by it.
  7. sparky

    sparky Active Member

    It seems like my rim has a tad bit of wear.

    Just thought I'd mention how JemmaUK said her kevlar brake pads (Clark's VCR) easily tore thru her rims.
  8. Happy Valley

    Happy Valley Active Member

    Yes Sparky, that's a lesson I learned on replacing disc brakes on my car. The high end, hard wearing pads wore the rotors very fast so that I ended up replacing rotors every time I did a brake job. The cheaper pads wore quicker but were easier on the rotors so I could get much longer life from the rotors. Pads were cheaper than rotors.