Brake Problem - piston stuck?

Hi
I'm not very confident in working on the brakes, but after my MOT the mechanic said that my front brakes were sticking (I had noticed this earlier in the week) and I should take the calipers off and give them a clean/service etc, I used the haynes manual to do this and found it wasn't that bad apart from when it said to push the pistons back in, only one would move, and when pumping the brake that one again was the only one to move. This seemed to be the case with both calipers? I am not sure what to do with them, I have ordered some red rubber grease as reading on here that is a good lubricant to use on the pistons themselves, but I don't know if they're broken or not?

Any advice on this would be very useful, I can normally pick things up quickly but I don't want to make any mistakes when it comes to safety.

Cheers

Originally Posted by CDMG

Hi
I'm not very confident in working on the brakes, but after my MOT the mechanic said that my front brakes were sticking (I had noticed this earlier in the week) and I should take the calipers off and give them a clean/service etc, I used the haynes manual to do this and found it wasn't that bad apart from when it said to push the pistons back in, only one would move, and when pumping the brake that one again was the only one to move. This seemed to be the case with both calipers? I am not sure what to do with them, I have ordered some red rubber grease as reading on here that is a good lubricant to use on the pistons themselves, but I don't know if they're broken or not?

Any advice on this would be very useful, I can normally pick things up quickly but I don't want to make any mistakes when it comes to safety.

Cheers

sounds to me like you need a caliper strip and clean,and new seals and dust covers if they have them

Any easy test is to swap the seals on the piston which is working with the one that isn't. If the non-working piston starts working after the swap, then the seals were the problem and new ones needed.

Assuming you've cleaned out any debris and gunk from underneath the seals, make sure they're installed facing the right direction (might be wrong on this but I think the OEM seal has a bevelled edge to ensure one directional fluid flow). Lubricate the seals first. You should be able to push them in by hand, although it should be a tight fit.

[yorkie_chris]

Originally Posted by Runako

Any easy test is to swap the seals on the piston which is working with the one that isn't. If the non-working piston starts working after the swap, then the seals were the problem and new ones needed.

Assuming you've cleaned out any debris and gunk from underneath the seals, make sure they're installed facing the right direction (might be wrong on this but I think the OEM seal has a bevelled edge to ensure one directional fluid flow). Lubricate the seals first. You should be able to push them in by hand, although it should be a tight fit.

With respect, that's a ridiculous way to do it. And yes you are.

Take them out, clean the crap from the seal grooves refit them with some red rubber grease in the grooves, smeared on the seals, and on the flanks of the piston and reassemble.


The pistons will always "work", the reason this sticky one isn't coming out is because the non-sticky one is moving with less fluid pressure.

Seals don't tend to go faulty unless they've been contaminated with oils. So swapping them around is a bit of a waste. The problem in 99% of cases is corroded crap and salt in the bottom of the dust seal groove.

There's your answer then.

Obviously a good idea to clean the grooves & seals (I mentioned that so got something right). Also meant swapping just to quickly diagnose, not to refit. I guess there are better ways to check seal condition. Or just replace as the manual suggests. T'was really a diagnosis suggestion, not a solution. Was unsure about bevel but heard some designs have them, so good to know for sure.

Thanks for the replies, Sounds right though there was a lot of gunk in the caliper spent a while with a tooth brush and brake cleaner and still struggled to budge some of it. How do i go about taking the pistons out? I'm not sure if I have the right tools to do it - what would i need?

[yorkie_chris]

Pump them out with the hydraulics. Wedge the free moving piston with something against the other side of the caliper to restrain it... then pump the stuck one out a few mm. Then restrain that one.

You move each piston a few mm at a time until one pops loose.


Obviously this will release all the fluid so you'll have to bleed them up afterwards.

Originally Posted by yorkie_chris

Pump them out with the hydraulics. Wedge the free moving piston with something against the other side of the caliper to restrain it... then pump the stuck one out a few mm. Then restrain that one.

You move each piston a few mm at a time until one pops loose.


Obviously this will release all the fluid so you'll have to bleed them up afterwards.

once ones loose will the other one come out easily? do you have any tips on bleeding the brakes as I've not done that before either I'm pretty much a beginner on brakes.
Also are these sufficient for the seals? or are there better quality ones from more reputable sites?
Cheers
http://www.ebay.co.uk/itm/Front-Brak...item20c5afc7ad

[yorkie_chris]

No. You need to edge them out at the same time if you can see what I mean.
I do it with a G clamp and swap the clamp between pistons depending which ones moves easiest.


If you mess it up you end up with one piston removed (and hence no fluid pressure) and the other one stuck fast.

So you need to go slow, take your time pumping them out, get them both even and do it 1mm at a time if you like!

If you do them 1mm at a time, then when the first piston pops out you will be able to remove the other piston with your fingers. Don't be tempted to use pliers, mole grips etc on them as you'll knacker them.


You'll also need to check the pistons for pits and corrosion. If in doubt bring it over here or to someone else who knows what they're doing

Originally Posted by yorkie_chris

No. You need to edge them out at the same time if you can see what I mean.
I do it with a G clamp and swap the clamp between pistons depending which ones moves easiest.


If you mess it up you end up with one piston removed (and hence no fluid pressure) and the other one stuck fast.

So you need to go slow, take your time pumping them out, get them both even and do it 1mm at a time if you like!

If you do them 1mm at a time, then when the first piston pops out you will be able to remove the other piston with your fingers. Don't be tempted to use pliers, mole grips etc on them as you'll knacker them.


You'll also need to check the pistons for pits and corrosion. If in doubt bring it over here or to someone else who knows what they're doing

Most of my tools and my toolbox are in Chester at the moment and I'm in Salford so I only have some common socket sizes and a ratchet and a set of allen keys i picked up from Tesco.

I think on this sort of job I'm best having guidance as It potentially could be quite dangerous if i mess it up. But I don't know whether to have a go on my own or not first as if i get it wrong the bike is stationary until I fix it :/