XBR front brake

[guest288]

When I've pumped the lever, the pistons move out, but one at a time. I think they should move out together so that the brake pad moves onto the disc level but this is not happening.

has the piston seal gone? Its hard to tell, but I don't think any fluid has leaked- the caliper is in bits, but i needed to force the pistons out so I put it all back together.

Any ideas on the wonky pistons?

[andy230]

hi dave,

sounds like you'll be stripping the whole caliper and replaciing the seals...     I think one of them is sticking, probably corrosion behind the seal/s is causing the piston to stick...  they should be pretty free.

Tho I am duff with brakes!  Someone may correct me if I'm wrong

a

[SteveC#222]

It might be worth doing a full rebuild, it's an easy job.  You can get stainless brake pistons at about £15ish a pot from Wemoto along with the seals.  Worth fitting a stainless brake hose too if you haven't already.

[dogman]

Hi dave,Dont want to teach anyone to suck eggs  but it may help you or someone else, place a single brake pad in the caliper,pump out the pistons till they touch the pad,remove pad and then the pistons should pull out,watch for loads of fluid as you do. Carefully prize out the seals,the first one is a dust seal the second is the brake seal.you can usually re use them unless they are ripped or swollen. Take a wire coathanger and cut with a pair of pliers,this cut end is the exact size to scrape the crap out of the grooves. look for corrosion,it will be a white powder type substance.this stuff builds up behind the seals and forces them in on the piston. when clean reassemble using new/old seals, clean pistons or replace with stainless.you will notice that the pistons will push in quite easily with your thumbs. Dont forget to grease the sliders on the caliper.I would reccommend a braided hose as it makes a major improvement in braking. Hope this helps,Wal

[guest288]

Thanks for the info- the seals appear ok- I've been told that one pot comes out slightly before the other one as part of the gradual braking effect. When both pots are out thats the full braking capacity reached?

[Steve H]

Is this an apposed piston caliper or does it have two pistons on one side, one larger than the other ?

[guest288]

Both the pistons are on the same side, although they are both the same side...

[guest7]

Yep, same side and same size.

You forgot to add that they are made of congealed Satan jiz. So says the man who has had to replace corroded pistons at virtually every pad change 

GC

[Steve H]

If they are the same size then the comment about one piston coming out earlier than the other is to create a more 'gradual' brake is misleading. The reason why comes out earlier is because one has slightly less crud behind the seal friction so it requires less pressure to move it.  If they had been different sizes then I would have expected one to more before the other.