rear brake pad not gripping properly

[Toby_2009]

Hi,

I have a Giant boulder MTB which has Disks. I have noticed that the read brake isnt gripping very well atall, I have adjusted the cable (loosened nut, pulled some through and tightened again) and the pads are jamming hard on but the diks not being gripped very well.

I think there is a change that WD40 vapour might have got on to it (whilst spraying gears) but if this is the case then it will only be a tiny, tiny amount so could it really have that bigger an effect? I have tried using white spirit to clean off any WD40 and its helped a tiny bit (I think) any thing else I can do?

Any thing else that could be the problem

Please help guys,

Cheers,

Toby

 

[Mr Pig]

It's not very likely to be the WD40. Even if you did get some on the disk, although it would make the brakes slip it would burn off. Well, enough of it would to return most of the braking performance. To check try a long decent holding the back brake on slightly to make sure you bake any oil on there.

Are the pads worn? Is the lever that pulls them on at the end of its travel?

And you shouldn't be using WD40 on the gears anyway! ;0) Use proper chain oil on the chain, the gears don't need anything.

Or white spirit on the disks. What you want for those is IPA (Isopropyl alcohol). You can get it from ebay or Maplins but any local printers will probably fill a bottle for you for nothing.

 

[Toby_2009]

It's not very likely to be the WD40. Even if you did get some on the disk, although it would make the brakes slip it would burn off. Well, enough of it would to return most of the braking performance. To check try a long decent holding the back brake on slightly to make sure you bake any oil on there.

Are the pads worn? Is the lever that pulls them on at the end of its travel?

And you shouldn't be using WD40 on the gears anyway! ;0) Use proper chain oil on the chain, the gears don't need anything.

Or white spirit on the disks. What you want for those is IPA (Isopropyl alcohol). You can get it from ebay or Maplins but any local printers will probably fill a bottle for you for nothing.

so ive dont it all wrong

I was told on another forum (shooting not cycling) that the WD40 had perished the rubber in the pads and that i need to get them replaced.

I have only have the bike 3 months and its probably only done 400ish miles so i wouldnt have thought they worn out

and no leavers arent at the end of their reach

 

[Mr Pig]

I was told on another forum that the WD40 had perished the rubber in the pads

Rubber? There is no rubber in disk brake pads. They're like the brake pads on cars, they're made of a very hard material. Rubber would melt!

Getting oil on them isn't good as there is no satisfactory way to remove but, while it will effect the braking, they'll still work.

Try turning the wheel with it off the ground. Pull the brake and turn it again. If you can see the pads move onto the disk and feel them drag on it, even if it's just a little, try the burning the oil off trick.

Failing that the brakes might need adjusted. On most mechanical disk brakes only the pad on one side moves. Take a look at yours and see if that's the case.

What happens is that the pad on one side sits very close to the disk and does not move. When you pull the brakes the pad on the other side moves in and pushes on the disk. Because the disk is quite thin the force bends it over to touch the fixed pad and the disk is clamped between the two pads.

As the pads wear down the disk has to bend over further. It will only happily bend so far though so eventually it gets hard for the moving pad to push it over to the fixed pad. To get around this problem the brakes are fitted with an adjuster to move the fixed pad closer to the disk.

Take a look and see if you can find a screw that moves the fixed pad. If you can then move the fixed pad over until it's just clearing the disk and no more, you're talking the thickness of a piece of paper here, not a millimeter. It's better that the pad touches the disk slightly than is too far away.

See how that goes :0)

 

[The Rookie]

I would second the piggy, and add that with discs you can see through the caliper (usually) at what is happening, if you can see daylight between the disc and pad its wrongly adjusted.

My Vuelta calipers have an adjuster on both static and fixed pad to get the responce nice and sharp!

Simon

 

[littledan77]

I found what Mr pig said to be exactly the problem I had with my disc brakes.

Possibly re-aligning the entire brake housing from step 1 to step n is the best bet (that's what I did). That will align the static pad the best and then fine adjustments can be made with the adjuster disc to get the best response.