rear brake rubbing noise?

if you have your bike on its centre stand and you rotate the rear wheel by hand , can you hear and feel the rear brake pads rubbing lightly on the disc? not binding but rubbing.

constant by the way - disc isnt warped

birdseye said:

if you have your bike on its centre stand and you rotate the rear wheel by hand , can you hear and feel the rear brake pads rubbing lightly on the disc? not binding but rubbing.

constant by the way - disc isnt warped

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Unlike drum brakes there are no return springs on disc pads so a slight rubbing might no be anything to worry about. I'm 1000 miles away and can't see or experience the rubbing! Check to see what happens when you apply & release the rear brake. Is the rubbing worse? Does the wheel bind slightly before changing to just the rubbing?

Taking the pads out and checking that the pistons move freely and that the sliding faces are free from crap then reassembling with a little high melting point grease can't do any harm. Unless of course you are one of those people that should not be allowed spanners in the first place.

And your disc is warped, only very slightly I grant you but all discs are. It's called run out and you will find a tolerance figure in a good workshop manual. This run out is one of the ways the pads are pushed back from the disc after braking.

I suspect you have nothing to worry about anyway but as I say checking should not do any harm.

John

High ferrous content discs can make a noise until the oxide layer is rubbed off. But the rear brakes on most bikes are more prone to sticking pistons than front brakes.

I had noise from my back brake and suspected it was getting warm though the final drive does warms it with normal use. I had cleaned the pads last summer and it was better, but a friend recently used the bike and commented the brake felt wooden.

Last week, I stripped the caliper and put in new seals. It wasn't badly stuck, but there's now no disc noise and the brake feels a lot better. I posted a how thread sometime last week.

The pads on disc brakes hardly move. Its small enough movement for the square section piston seals to act as return springs. Eventually pad wear allows the piston to slip through the seal but most of the time the seal flexes rather than sliding. Any debris between the pair of seals can cause the pistons to stick.

I have had problems with sticking rear pads on 4 bikes in the last couple of years including, today, my 7k july 13 GSA. It becomes aggravated as the pad wears and the piston is more extended. this problem is all over the forums for all bikes and is due to the seals becoming swollen or crap/ corrosion in the seal grooves. I paid last year to have the dealer do a caliper strip on an Pan st1300 still under warranty and with notably tricky linked ABS system but have cured the other three myself. I have found that with the caliper off and pads out if you simply cycle the pistons from fully in to fully out several times ( you may need to use a G clamp to assist at first) you can feel the pistons easing up and by the end they slide in with very reasonable manual force after using the pedal to extend them. This procedure isn't nearly as thorough as removing the pistons, cleaning the grooves , replacing the seals, re bleeding etc but it is an awful lot less hassle. I think the extended motion of the piston lubricates the o ring and shifts the crud. Putting red grease on the extended piston also helps free things up. The satisfying part of this procedure is that you can actually feel the difference while the caliper is still connected up. Anyway I just add this for people who don't want to go the whole hog in stripping the caliper or paying a dealer to do so. Maybe give it a try.

Actually that sounds normal to me.

flatdog said:

Actually that sounds normal to me.

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Yeah I agree that when the caliper is working as it should you can push the pistons back in using thumb pressure. But when they have been sticking they are very hard to push back the first few times ( hence use the g clamp) but gradually become easier until they are slippy as a slippy thing. Be interested in views on this -but empirically it has worked three times in a row on different bikes.

I did this with my back brake last summer but it was never really right. A full overhaul sorted it. I used new seals (£18 a set) but the old seals looked fine. It just needed a good strip and clean.

Next job is to do the fronts - stitch in time, etc. But they come as a set with pistons at £60 a side, so I'll strip and check before ordering parts. If it simply needs a clean there should be no need to fit new parts.