Disc brake not smooth anymore, vinration whenbraking

jozi

Noticed last week that my rear disc has started to vibrate or something, maybe not the right term to describe it. It feels as if I can feel the groves on the disc through the pads when I brake as well as there being a noise, both of which weren't there when I got the bike a few weeks ago. Braking performance seems to be as good as it was since I got the bike, no problems stopping.

I get a squeal as well from time to time with this wet weather, bit of copper grease on the disc solve this?

Gavin

jozi wrote: »

Noticed last week that my rear disc has started to vibrate or something, maybe not the right term to describe it. It feels as if I can feel the groves on the disc through the pads when I brake as well as there being a noise, both of which weren't there when I got the bike a few weeks ago. Braking performance seems to be as good as it was since I got the bike, no problems stopping.

Could just be the brake pads wearing in.

I get a squeal as well from time to time with this wet weather, bit of copper grease on the disc solve this?

Yeah it will stop the squealing, but won't actually be much use in stopping the bike any more. Grease lubricates, reducing friction. Which unfortunately is how brakes work.

jozi

I never really understood the idea of copper grease, thinking grease would as you say lubricate them.

Would it take this long to ped the pads in? I've at least a few hrs a week of cycling.

sean_d

You put copper slip on the piston/pad interface (the back of the pad) to reduce vibrations - not very common in cycling, think its something that carried over from cars/motorbikes. The ramifications for an errant drop of grease are quite big.

Is there enough braking material left on the pad? Sounds like it could be worn through. Otherwise, check for any rogue pieces of stone or grit in there, and generally give it a good clean.

jozi

I litter only have the bike about 3 weeks so I can't see it being worn pads, couldn't be that soon?

The disc looks fine, a little bit of brake dust on it but the contact area looks clean. I'll pop the wheel of this evening and take the pads out and see what they are like.

The strange thing is that it's not always noticable. I've a feeling that when it's wet it's fine and once dry i can notice it and even then sometime it doesn't do anything abnormal.

Greyspoke

Check that all the bolts holding the disc on the hub are tight (don't overtighten them though - just make sure one isn't loose). Make sure the disc is still running true - if its taken a knock it could have a bit of a wobble in it. Although the bike and brake pads are new, many brake systems come with relatively soft resin pads which give good braking but wear out quickly especially in wet and muddy conditions. It's quite possible that you've already worn them down to the metal backing.

jozi

I had a quick check of the disc to see if it was lose but really need to do it properly and not at the side of the road. I have no way of tightening them if they are lose, they are hex bolts :rolleyes:

The caliper seems well tightened on to it's fixing. I'll check the pads later. Am I beter of taking the caliper of or the wheel to get at the pads?

Greyspoke

Fixing bolts may not be hex bolts - they're often torx bolts which require a special key. Chances are they're not loose anyway. As for removing the pads, just take the wheel off - it should be reasonably apparent how to remove the pads - usually a slim bolt through the caliper and a spring clip holding them in place

jozi

Yeah your right they are torx and they don't appear to be lose.

Took the wheel out and the pads. There's about 2-3mm left on both pads. I can't get the disc centred in the caliper now. I've tried to centre it a good few times but it keeps rubbing on the pads. There seems to be something sticking out somewhere cause I can hear it rub, similar to what I could fel when braking.

I'll drop into the bike show in the morn unless someone in DIT Bolton st wants to have a quick look tomorrow?

jozi

Brought it into Cycleways last week. As much as I tried to explain to the guy I couldn't get him to understand what I was experiencing. He just kept telling me that the calliper was binding, which I already knew because I couldn't get it centred properly.

Took it out to Halford in Blanch and explained the problem to the guy there, told he to take it for a spin. He reckoned the pads didnt bed in right and told me to sand them down a little and see does it make a difference. He wouldn't get looking at the bike so said I'd give it ago.

Didn't make a difference It took me about 2 goes to get the front calliper centred (had the wheel of). Spend ages trying to get the rear one right but can't manage it. While sitting next to the bike with the wheel spinning I noticed the disc was of centre.

Looking from the side you can see the disc edge move in/out (towards it's centre) by the calliper. So I suspect the disc moving in/out is causing the vibrations.

I'm guessing it should be covered under warranty but in the case it isn't how much is a new disc (pads are about 15 I think)?

Single Malt

A mtb disc is never 100% straight. It cannot be, as it is punched out of sheet steel. The disc being straight or not has no impact on vibrations. The pads themselves, or the design of the frame disc mount have bigger impact on vibrations.

Some frames are prone to them due to the angle the forces are transferred to the frame. This causes resonance in the frame, hence a squealing and vibrations that can be felt through the frame. Sometimes its just that the natural vibrations of a certain disc brake hit a resonance frequency of a frame. This is the most common reason for excessive vibrations, and new pads of a different brand should fix this, as they will vibrate at a different frequency.

wotdef

To center the caliper loosen the bolts that give sideways movement, pull brake lever making sure caliper moves to a central position and gently at first tighten bolts. To straighten disc use an adjustable spanner. Have a look at bikeradar.com in the tech links

jozi

I realise that the squealing is caused by vibrations, but those vibrations can't be felt or at least not like that. My front disc squeals a little but I can't feel them. There's no squealing from the rear, only the vibrations.

It's more as if one of the spokes from the disc come in contact with the pad or calliper. I'm not sure how to explain it properly but put it this way, if I was driving my car and all of a sudden there was a pulsing when I brake I would be concerned, obviously something is wrong al of a sudden and this is what happened here. The brakes were fine, a little squealing and then all of a sudden there's this vibrations (maybe pulsing is a better word for it) and noise coming from the rear when I brake. The brakes work fine from what I can tell it's just not very confidence inspiring.