Disk brake trouble

Icyseanfitz

hey guys i just installed a new set of avid elixer 5's onto my bike and the rear one is rubbing really badly (as in when i try to spin it it just wont spin at all without a bit of pressure behind it), its rubbing on the left facing from the back, its also rubbing the mount (already badly scratched from it), im at my wits end with it as ive tried realigning it countless times by loosening the cps bolts (the ones facing upwards correct?) and holding the brake firmly while tightening the bolts again,
any ideas lads?

studiorat

The disk is rubbing the mount? Does it need a spacer for the caliper? What size are the rotors?

You should try gently prying the pads apart with a screw-driver. Sometimes the brakes close up if they are pulled when not on a rotor. I've found with some disk brakes you need a a couple of washers or shims on the rotors to move them also. Particularly with Hope ones I've had in the past.

Would these sort out the problem? http://www.chainreactioncycles.com/Models.aspx?ModelID=356

Icyseanfitz

il throw some pictures up, hopefully they will help somewhat







i dont think the caliper is too high or low i think its just not aligned properly with the rotor and the lossen hold lever and tighten just isnt doing it for me

Gavin

Those pictures are woeful. You'll need to get some washers and use them to align the caliper correctly

Icyseanfitz

best i could do with my crappy phone so ive to buy something to align the brakes even though they are brand new? wouldnt new washers only serve to increase the height of the calipers? height is grand its that the rotor is rubbing on the left side constantly

Tommyadams

Yeah just need shim(s) for correct spacing, had the same problem with my juicys though im only guessing as i can't really see on the pics.

Icyseanfitz

again wouldnt that only serve to increase the height of the caliper?

langdang

If the disk is rubbing off the mount then shims aren't gonna help are they?
You can shim a disk out further from the hub, or shim a mount in closer to the hub, but both of these actions will only make it worse if I'm understanding the original post correctly?

Check your pads are installed correctly, and push them back fully in their bores and try again!

EDIT - did you already have disk brakes on the rear and these are just an upgrade? (If you already had disk brakes and they weren't rubbing then your frame is ok and it must be the new setup)
Did you re-use existing mounts, or did you get new ones? There isn't a washer between the frame and the mount already is there?

Icyseanfitz

langdang wrote: »

If the disk is rubbing off the mount then shims aren't gonna help are they?
You can shim a disk out further from the hub, or shim a mount in closer to the hub, but both of these actions will only make it worse if I'm understanding the original post correctly?

Check your pads are installed correctly, and push them back fully in their bores and try again!

exactly the rotor is rubbing the left hand side of the caliper (pads and mount) so moving the rotor out or mount in will make it worse, any idea whats the best way to push back the pistons?

Icyseanfitz

i had juicy three's before this and they certainly where not rubbing as much if at all, and everything is brand new with these elixer 5's

langdang

Icyseanfitz wrote: »

i had juicy three's before this, and everything is brand new with these elixer 5's

TRy using the mounts from the old disks unless you've sold em or the new disks are a different diameter. (They should be the same but maybe there's a difference)
My brakes (Hayes) came with a little plastic rectangle with wedged ends to force in between the pads to push back the pistons. A large flat blade screwdriver would do I suppose. Google it I'd say - I've never used anything except that tool I have( also doubles as a thing to block up the brakes if you have a wheel removed so you can't accidentally apply the brake and push the pads together.

Icyseanfitz

i will go about doing all of the above i take it to push the pistons back the caliper has to be loose right? how much force do they take to push back? i really dont want to screw these brakes up as ive no bleed kit at the moment

langdang

On my Hayes brakes you don't need to release anything, just be gentle.
You have the manual ya?
http://www.sram.com/_media/techdocs/95-5015-016-000.pdf
Have a look at the section on pad replacement.

But pads being off doesn't explain the disk rubbing on the mount...
Is your axle properly aligned?
Are you sure there isn't a washer between the frame and the mount?

gman2k

It looks like an IS fit frame, and you have a post mount caliper attached to an adaptor.
(from the bad photos that's what I'm guessing)

Q1. What brand of adaptor are you using?
IMHO, Shimano adaptors are the only ones worth buying.
Q2. Does the adaptor size equate to your rotor size? I.E. in general you would fit a PM to IS 160mm adaptor in your instance - again if I'm guessing correctly.

If the rotor is rubbing against the adaptor, then you have installed it incorrectly, there should be no major need to use shims between frame mounts and the adaptor if you have a Post mount caliper, as you can straighten it out at caliper more easily.
It is possible you have put the adaptor on backwards.

Icyseanfitz

guy over on epicmtb just asked about having a washer as well guess what i .... i have em on both front an back they came on the screws with the brake so i assumed that they should go on but clearly they shouldnt, the wheel is at least spinning now although i still have a little rubbing but il sort that out with all the great suggestions here, thanks a million guys ye are life savers

studiorat

Oh dude!! Scratches!! Yeuch!!

Icyseanfitz

studiorat wrote: »

Oh dude!! Scratches!! Yeuch!!

il spray paint it black and it will be all good as new that or il just take the mount from my juicy three and bobs your uncle lovely looking bike (although having a mtb with no scratches doesnt seem like a very common thing), speaking of which il be putting the beauty up in the image topic shortly as soon as i learn how to take a halfway decent picture with this damn phone

AstraMonti

Sorry to hijack your thread, but do your brakes feel soft? I got the same a week ago but even after the bleeding they are very very soft. I mean the lever almost touch the handlebars and I 've got no clue what's wrong.

cdaly_

Bleed them some more.

A disc brake uses a wobble (runout) in the disc to push the pads back a bit when released. If there's too much runout, the pads will move back too far needing more lever movement. If you pump the brake levers (with the wheel stopped) they should come hard after a bit. If they don't then there's still air in the system.

PS. I'm not sure how bike brake bleeding is done but I suspect a gravity bleed will not be enough to get air out. You're better off using a one-person bleed kit.

thehangtenguy

Guys, bleeding the calliper correctly on the Avid system is important.
With the bleed kit, if used correctly, you remove air from the system and create a vacuum so the calliper pistons open fully on release of the lever. The system is not designed so run out in the disk opens the pads.