Disc brakes & vibrations

[SatNavSaysStraightOn]

Quick question

I've got a 2nd hand mtb (via a cc member & the for sale forum) which has disc brakes and recently the rear brake has started to make some noises that are not dirt related. The front brake behaves normally and this is not something I have had with my old mtbs with disc brakes.

It's not the noise that concerns me, more the vibrations coming up through the seat which without putting too finer a point on it out do any vibrator I have every had.

Is there are problem or can I just go on 'enjoying' them?

 

[lpretro1]

Are the brakes hydraulic or cable type disk brakes and what make/model? You need to have a look at what is going on. If you squeeze the brake lever can you see the rotor deflecting at all? Are both pistons moving out and going back smoothly and equally? If the rotor is deflecting then the brake needs re-centreing, If that looks ok then take the pads out and have a look at them - do they look glazed, have they got anything trapped in them? Is there plenty of meat on the pads or are you down to the metal? Has the pad return spring got jammed?
Vibration suggests the brake is possibly 'juddering' under load which may indicate some contamination on pads - they may be grabbing and releasing in quick succession ? Cable disks can be a little prone to glazing.
I'd not ride it until you ascertain the problem as you could cause damage

 

[SatNavSaysStraightOn]

Are the brakes hydraulic or cable type disk brakes and what make/model? You need to have a look at what is going on. If you squeeze the brake lever can you see the rotor deflecting at all? Are both pistons moving out and going back smoothly and equally? If the rotor is deflecting then the brake needs re-centreing, If that looks ok then take the pads out and have a look at them - do they look glazed, have they got anything trapped in them? Is there plenty of meat on the pads or are you down to the metal? Has the pad return spring got jammed?
Vibration suggests the brake is possibly 'juddering' under load which may indicate some contamination on pads - they may be grabbing and releasing in quick succession ? Cable disks can be a little prone to glazing.
I'd not ride it until you ascertain the problem as you could cause damage

thanks - will have a look - I tend not to use the rear brake (I know) because I have a bad left hand and the grip is questionable in my left hand as it is and I am so used to only being able to really brake with the right hand (front brake)... anyhow - will check out what you say tomorrow. Is it obvious how the pads come out to check them?
(I have 2 other bikes so no major issues wrt to safety, I can easily use those whilst I sort this one out!)

OK - the brakes are:
Front Brake: Shimano BR-M505 hydraulic disc brake, dual piston, 160mm rotor
Rear Brake: Shimano BR-M505 hydraulic disc brake, dual piston, 160mm rotor

It is this bike http://www.evanscycles.com/products...m_medium=Awin&utm_campaign=Affiliate#features

 

[Arch]

Once you've worked out the problem, can you tell us how to replicate it?

 

[lpretro1]

The fact that you are not using the brake much would indicate the 'glazed' pads problem.Checkout the disk rotor deflection first. If you then need to remove check pads then remove wheel and then there is a split pin holding the pads in which you will need to pull out. Once you get that out pads should pull out dead easy. Take care not to put your fingers on the pad material as this can contaminate them. If they are glazed then get a piece of fine sandpaper/emery and buff the glaze off. Refit and then recentre brake and try them out. Worthwhile cleaning the disk rotor with IPA or proprietary disk brake cleaner as well in case anything has got on there and check rotor for true. If in doubt fit new pads and try it.
Check also that disk rotor bolts are tight

 

[SatNavSaysStraightOn]

OK - photos...

front pads

rear pads...

Am I correct in guessing that the left hand rear pad is going to need replacing?
does anyone have any ideas on the wear pattern please? Remember I have not had this bike from new - only for about 8 weeks or so.
thanks

 

[ianrauk]

Plenty of life left in those pads.
But looking at the wear, the callipers are off center which may be the reason for the vibration.

 

[Sara_H]

Quick question

I've got a 2nd hand mtb (via a cc member & the for sale forum) which has disc brakes and recently the rear brake has started to make some noises that are not dirt related. The front brake behaves normally and this is not something I have had with my old mtbs with disc brakes.

It's not the noise that concerns me, more the vibrations coming up through the seat which without putting too finer a point on it out do any vibrator I have every had.

Is there are problem or can I just go on 'enjoying' them?

Can I borrow your bike please

 

[Cubist]

As Ian says, there's plenty of life left in them. They need changing at 0.5mm, unless the whole setup becomes spongy.

The uneven wear will be down to caliper poistioning. It's a simple fix though with Deores. Stand the bike upright and slacken the caliper mounting bolts so that the caliper moves sideways easily, then simply apply the brake. Get Stuart to hold the brake on, and do up the caliper bolts to finger tight, then a quarter turn alternating between the two screws until the bolt is nipped up firm but not massively torqued. Release the lever and check the wheel spins freely without binding at any point on the rotor. Job done.

 

[byegad]

Once you've worked out the problem, can you tell us how to replicate it?

Tut! Tut! Tut!



Mmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm!

 

[SatNavSaysStraightOn]

Can I borrow your bike please

you'll have to visit it. tis interesting though... have to stand up from time to time to get away from them!

 

[SatNavSaysStraightOn]

Plenty of life left in those pads.
But looking at the wear, the callipers are off center which may be the reason for the vibration.

As Ian says, there's plenty of life left in them. They need changing at 0.5mm, unless the whole setup becomes spongy.

The uneven wear will be down to caliper poistioning. It's a simple fix though with Deores. Stand the bike upright and slacken the caliper mounting bolts so that the caliper moves sideways easily, then simply apply the brake. Get Stuart to hold the brake on, and do up the caliper bolts to finger tight, then a quarter turn alternating between the two screws until the bolt is nipped up firm but not massively torqued. Release the lever and check the wheel spins freely without binding at any point on the rotor. Job done.

thank you. reassuring. will try to sort the positioning at the weekend when I actually have another half who can hold the brakes on for me!
@Cubist - tis a little bit cleaner than when you last saw it still getting those vibrations though (had them at the weekend as well...! now you know the real reason I am so slow going downhills....!)

 

[Cubist]

thank you. reassuring. will try to sort the positioning at the weekend when I actually have another half who can hold the brakes on for me!
@Cubist - tis a little bit cleaner than when you last saw it still getting those vibrations though (had them at the weekend as well...! now you know the real reason I am so slow going downhills....!)

Explains the flushed look perhaps! Took me hours to get all the mud off everything. The kids pointed out I had panda eyes! Great fun though.

 

[Rohloff_Brompton_Rider]

Is the rotor bent? Or the mounting bolt holes worn?

Looking at the wear pattern, I'd say you probably have sticking piston guides or if it has two pistons a sticking piston.

 

[mrandmrspoves]

P

Can I borrow your bike please

Perv! :-)