Disc Brake

Can't say I've ever had the problem with my bike disks, but since the theory at work is largely the same as automotive brakes, here's my .02:

Is the pad material the same as the old ones? Have you tried automotive brake cleaner? I asume the surface area of the pads is the same, but if not that could be a cause. Also, if they are hydraulic, are they bled 100% propperly? (You should be able to feel it if they're not)

If all these check out OK, then I would try this: Lightly scuff up your disks on both sides with the same 220 sand paper. Then install the pads as normal, and make several stops at perhaps 10-30 second intervals, gradually increasing the braking force each time untill you come almost to a panic-stop level. This gradually put heat into the system without building up excess, and allow the pads to bed with the rotors. Essientally the same as bedding pads on a car, just modified to work with bike components / forces.

Make sure that your hydraulic fluid is not leaking onto the pad.

What I do: blow torch, or if the girly is out shopping, the hotplate in the kitchen.

Do wait for it all to cool back down again before attempting to reassemble.

rdl520 said:

I have disc brakes. The brakes got contaminated with oil and I thoroughly cleaned the rotor with alcohol and replaced the pads the pads with new ones. They still slip.🙁

alcohol is a polar solvent and not really suitable for removal of oil. you need a non-polar solvent like petroleum ether (white spirit). pour some in a paint tray and leave them to soak for an hour or so. remove and dry with a heat gun.

as another poster suggested make you you aren't bleeding oil still.

--brett

Thanks to all who have posted.

The OEM brakes are cable. We did use automotive disc brake cleaner on the rotor first.

Someone advised that this was to be expected of cable brakes and hydraulic brakes would solve the problems. Does anyone have experiance adding aftermarket hydraulic disc brakes?

Of course hydraulic brakes would perform better than mechanical in a static head-to-head comparison, but that's not your problem. It sounds to me like you have had a sudden drop in performance compared to a previous period on the same set of brakes. I have mechanical disk brakes and I've never noticed a drop off in performance. ( I don't really maintain them either, to be honest.)

My original conclusion still stands: Since you've eliminated the cleaner and I'm going to assumeme the surface area is the same, I would put it down to pad material and break-in. Clean the old pads REALLY well with automotive brake cleaner, and re-install them. If you really can't get them clean, then try burnishing the rotors and bedding the new pads to them as I described above.

If you didn't have any problems with the performance of your mech. disks prior to this problem, then I woulden't bother going up to hydraulic unless your doing some serious DH or something. They're not cheap, they're harder to maintain, and they get brake fade if they get too hot. (Then you'll really have a problem stopping, lol)

Threaded is spot on, blow torch the rotors. Or replace the them. They don't work with any oil on them, at all, unless you want to ride hard for a few hundred kms to burn off the oil anyway.

There is no readon why cable discs won't stop well, but hydraulics are more powerful.

Remember, it ain't the pads, its the rotors (but you did the right thing replacing the pads, just hope they now haven't got oil on them otherwise it'll take a fair few kms to wear off)