disc brake adjustments - puzzled!

[montage]

I have never used disc brakes before, and I am doing up a full sus mtb with these fitted.

I had to replace the rear wheel axel of this bike - so this could be the problem... but I shall explain:

The "braking pads" (not sure of the technical name for these) rub on the brake disc - well to be more specific the right hand pad rubs against the disc brake... The reason for this being that the "block" the brake pads are held in is too far too the left - so I am looking for a way to move the "block" right slightly.

This could be a problem with my rear wheel alignment/spacers on the axel which has moved my bake wheel slightly to the right.... though adjusting this could be complicated due to limitations of spacers on the axel etc.

 

[arallsopp]

What's the model? Avid7s have big red rings that you can use to move the pads in / out. IIRC, they shouldn't centre on the disc anyway, but I can't remember which way they should favour. Perhaps just loosen off the cable a bit and see if that cures things.

The Shimanos on my other bike are also adjustable, so I'd be surprised if yours weren't.

When perfectly adjusted for me, mine 'ting' in the rain.

 

[Cubist]

It depends on the make of the brakes. For example, Hayes have two mounting bolts which hold the caliper to the fork leg or frame mount on the calipers. If you loosen them once the wheel is in place the whole caliper can move freely left or right. All you need to do is loosen the bolts, hold the brake on at the lever, and tighten the bolts up. This centres the brakes to the rotor.

 

[byegad]

Spacer washers are used to position the caliper. If the new axle has moved the whole wheel only a mm or two to the side then that would cause your problem try dismounting the caliper and fitting with different washers to shim it correctly.

 

[montage]

I will look into these comment, thanks!

And the everything is sram 3.0 as far as I can remember - so cheapo stuff I believe

 

[Globalti]

Aim to get the disc parallel to the centre seam joining the two caliper halves, if there is a seam.

You can bend the disc as well to get it running true.

 

[montage]

Ohhhhh so the disk is adjusted not the "block" or brake pads (technical names for these? ) ..... I shall look at this.

 

[RedBike]

No, you adjust the brake caliper.
Assuming there isn't a slot /groove to allow you to adjust the calipers position you fine-tune the calipers position by using washers / shims.

 

[Globalti]

What I should have written was: "Aim to get the centre seam joining the two caliper halves, if there is a seam, parallel to the disc".

 

[02GF74]

the position of the hub is adjustable to some degree on the spindle but usually this should be the same across different brands.

the caliper can be adjusted using shims - very thin washers - but this allows adjustment in 1 direction only. and yse, it is acceptable to have differnt number/thickness of washers on each bolt. this is due to tolerance in the different manufacturers frames and calicpers, and hubs too I guess.

posting photo would be best for more advice.

 

[bonj2]

montage,

a) the term for what you are calling the "block" is the 'caliper'

this may only apply if it's a hydraulic brake, but here goes:

There should be two bolts that bolt the caliper post mount adapter on to the frame, and two bolts that hold the actual caliper itself onto the post mount adapter (sometimes called the caliper positioning bolts or 'CPS bolts').
These two latter bolts adjust the caliper positioning - as the hole in the caliper for them to go through is like an elongated hole, so when they're loosened the caliper can move side to side before being tightened.
Try the following procedure for caliper positioning:
* make sure the wheel is on correctly in the dropouts and the QR is done up.
* loosen the caliper positioning bolts (but make sure the caliper is pushed flush up against the post mount adapter).
* pump the lever a few times, then pull it on hard - this should move the caliper into its optimal position
* tighten the caliper positioning bolts. (you might need a helper to hold the lever on while you do this.) The step of pushing it flush against the PM adapter is important so that this step doesn't cause it to move up and down the bolts in the process of tightening, and thus possibly also move laterally, which you don't want.

It may still drag a little bit after this but as long as it is not causing the wheel to actually slow down much it doesn't matter. i.e. spin it and if it stops within one revolution it's too much, if it carries on spinning but you can hear a bit of a 'shoosh' noise where it's touching slightly it's probably ok - use your judgement. You can also true the rotor with an adjustable spanner if you notice that it's out.

 

[02GF74]

montage,


There should be two bolts that bolt the caliper post mount adapter on to the frame, and two bolts that hold the actual caliper itself onto the post mount adapter

interesting, my calipers (shimano and magura) have lugs thaqt bolt directly to the forks and frame at the rear. I have noticed that the shimanos on sale and indeed a lot of other brakes seemto know be of the type as you describe thus requiring a bracket.

 

[bonj2]

interesting, my calipers (shimano and magura) have lugs thaqt bolt directly to the forks and frame at the rear. I have noticed that the shimanos on sale and indeed a lot of other brakes seemto know be of the type as you describe thus requiring a bracket.

they must be old school direct post mount then, could be that you've got manitou forks?
most frame and forks now are IS mount, which means the bolts go parallel to the axle of the wheel.
Most calipers are post mount, and the adapter serves as a convenient way of enabling the CPS bolts to be engineered into the system. Some calipers are direct IS mount - hopes used to be, but newer hope calipers are post mount. The old ones required a variable amount of washers to be inserted to make the adjustment instead.

 

[montage]

Just been out and sorted them out... thanks for all the help

I guess I need new "pads" as the brakes are crap though!

 

[arallsopp]

Possibly a little late to say this, but you mustn't touch the braking surfaces as any kind of residue left there will ruin performance. I've spent the last 300 miles burning off the oil from an affectionate mishandling by my wife. Petrol seems to clean the disc pretty well.