Bicycle Mechanics - disc brake issues...
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03-26-08, 02:05 PM
I have a set of shimano m-7565 disk brakes. I'm having a problem with my rear one. I bled them a few weeks ago, and they worked fine after that. But during my working on them my tool tray fell off my workstand.. and mineral oil got onto the Back of my rear pads the metal plate side... my front brake you can totally feel the friction of pad on disc the rear one doesn't feel like its really there. Might the oil have ruined my rear pads? it mean it works but not real good. Do I have to replace both my pads and my rotor or just my pads??? any help appreciated.http://www.pic4ever.com/images/17.gif
03-26-08, 07:42 PM
I wouldn't think the brake fluid would do that much damage...maybe it just left an oily film that's affecting the braking? I'd try cleaning the pads' friction surface and the rotor with a degreaser...
03-26-08, 07:51 PM
make sure the brake degreaser is a Brakleen or similar no-residue type, non-chlorinated.
03-26-08, 08:33 PM
sounds like the caliper needs a rebuild. O rings are leaking.
03-26-08, 08:34 PM
And if oil does get on the pad surface, it ruins them because they soak it up which contaminates the pad.
03-26-08, 08:39 PM
Brake cleaner for the rotor just in case and I'd suggest boiling the pads in water to remove any possible oil in the pad material. Boil the pads face up so the oil will float up as it leaves the friction material. If you notice any oil on the surface of the water after be sure to pour it off before removing the pads or it could soak right back in as they pass each other.
If it's still not gripping well then I suspect your caliper isn't sitting with the pads flush with the rotor surface. This means the pads are forced to flex the rotor before making full contact. And that's not good. You can often see this if you pull the lever aggresively while looking closely at the rotor. Any sign of flexing in either direction should be fixed by aligning the caliper with shims or having the brake mount spot machined. There's a kit that the better equipped shops can do this with and it aligns the mount to the axle to a very high degree. I had this issue on one frame and the spot machining did the trick.
If it USED to be good then it's far more likely oil on the pads you didin't notice or the caliper didn't remount the same as before.
03-26-08, 08:44 PM
yea, but the oil got on the pads somehow. Which probably mens his caliper is leaking. Or they got contaminated with chain lube or something.
03-26-08, 08:49 PM
He said he dumped his workstand shelf and the bottle of oil flung out and spilled on everything.
03-26-08, 09:04 PM
Oh my bad.
Replace pads if boiling them doesn't work.
03-26-08, 09:07 PM
Honestly, I would just clean the caliper well and replace the pads. I've tried the boiling and whatnot, and while it works better, it's still not as powerful as new. And just use rubbing alcohol to clean the rotor.
03-26-08, 10:48 PM
Well I'll try the boiling tonight with the added cleaning of the Rotor with some Brakekleen tomorrow night when I get off of work.
THanks for all your very helpful and insightful comments and suggestions. BikeForums is a great resource for all of us.
heres a pic of my ride.
03-26-08, 10:52 PM
I would love to replace the rotor and pads... but money is an issue right now... And plus throwing money at stuff sometimes isn't the best way...
and if any asks.... this was originally my XC race bike, I moved from Santa Rosa California to Portland oregon and haven't found any good trails close in. So unfortunately this is a very temporary Commuter. Thus the skinny ass tires and lights.
One guy commented What the hell did you build this for... and it wasn't commuting rest assured. This summer mt. hood single track is calling my name.
Thanks again Guys and Gals.
03-27-08, 11:54 AM
well unfortunately the boiling the pads and cleaniing the rotor with alcohol didnt' work. So I'm off to shop today or tomorrow to buy new pads. Darn.
03-27-08, 01:35 PM
There's bazillions of great trails all along the stretch between Portland and the Dalles. I've hiked a few of them when the wind wasn't high enough for sailboarding. It's a bit of a drive to hit the areas that are good but there's lot's of variety. You'll have knobbies back on that baby in no time.
Sorry the boiling didn't work for you. I've boiled out DOT brake fluid from pads with excellent results. Perhaps the mineral oil doesn't respond the same way.
I've also had less than great luck using alchohal to remove oil and grease. It's really not the right solvent for petrochemical based goops. You may want to still use some BrakeKleen and see if any more blackishness comes off in the rag.
I also prefer to use paper towels for such cleaning to avoid any oil that may be on the shop rags just migrating onto the metal. Remember that solvents like this don't neutralize the oils. They just thin them enough that you can wipe it away easier.
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