Couple of disk brake questions

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Bodhbh

Guru
Possibly silly question, hope so, and therefore has a simple answer...

Got around to some well overdue maintanance last night, which included changing the rear disc brake pads on my MTB (old rockhopper with Shimano Deore M525 hydraulic brakes, bought the standard Shimano M525/M475 pads). Only 2nd time I've done it, bit fiddly, but get the pads in. Only problem they're about as thicks as 2 doorsteps compared to the previous, worn old pads and once installed between the pistons impossible to fit the disc back between them, in fact there's no dead space there period. I did not compress the lever while the wheel was out - so, question is any trick to open up the pads a little?

(changed the front pads not so long ago, and while they might have required opening a bit with by twisting a screwdriver between the pad mount, and a bit of a inital disc rubbing there certainly was some space there).

Other question: to sidestep the issue (was like 1am at this point and off on the bike for the weekend after straight work today) I swapped the rear brakes for a pair off another bike - they work, although very spongy and seem poorly aligned, ie one pad fair distance from disc, other rubbing. This a question of 'bedding' or really need to get some shims to fix the calipers in the right spot.
 

bonj2

Guest
push the pistons back in, if necessary with thepads out. When the pistons areright back in the cylinders, putthe pads in, then with the rotor between the pads, ram a little thin sliver of plastic (the vacuum-pack type packet the brake pads come in is ideal) between the rotor and the pad, on either side. Then pump the brake a bit, then takethe plastic out. the pads should have then centred with a little bitof breathhing space so the rotor doesn't rub.
 

Steve Austin

The Marmalade Kid
Location
Mlehworld
what bonj said is sort of right, but you shouldn't ever touch the pistons with anything that could score/scratch/dent them. Easiest way is to get a large screwdriver and put it between the pads and twist it slightly.you need to do this slowly and gently. this will compress the pistons slightly. Better to do this with the old pads in before you remove them. you may need to remove the reservoir cover if you have excess fluid in the system.
To centre them. undo the bolts on the caliper, the ones holding it to the frame/forks. squeeze the lever, and hold it to the bar with a friendly assistant or elastic band and tighten bolts.New pads quite often rub a bit.
 
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