brake pistons out of line

Dear LB community,

Need some advice regarding brake caliper. I changed my brake pads over the weekend and unfortunately the interior brake pad (facing away from the bike) was completely worn on both brakes. No surprise then that two pistons from one side were extended more than the other.

I think, I should buy new brake discs and change the brake calipers entirely (the discs have over 14k on them, so why not). Is that the right thing to do or is there something i could try to fix the calipers?

if it’s the right thing, how the hell do I go about changing the brake calipers? What parts do I buy? I am asking this because I am not sure that the pistons themselves are enough to change. This is what i am currently looking at:

No you don’t need to change the calipers as long as the pistons are moving freely.

put the old pads in, shove a spanner between them and force the pistons back into the caliper. You should unscrew the lid of the master cylinder to let the fluid back up the pipe. 

clean the calipers first before pushing the pistons back 

I use one of these ,they are not expensive 


Sounds like you need to give them a good clean (toothbrush and brake cleaner only).

I seem to remember (could be wrong - it’s been a while) An advice I was given his to put some copper grease on the pistons before pushing back in.

I remember it was a bitch to do and Matt always had to give me some help. We never had to unscrew the m/c lid.

You’ll need a socket to hold the two in place while you push the others. Never use anything sharp as you can scratch the piston.

However Wise’s tool looks like a good one… I wish I had it when I was doing them!

Do not ever use copper grease on caliper internals, a smear on the back of the pads is fine, a smear on the mounting bolt threads is fine, on the calliper internals it is a no, no, no, do not do it. If you’re in any doubt when it comes to brakes consult a qualified professional. Brakes is critical!

Other than replacing the pads and If you’re competent to proceed you should:-

Callipers - If one piston is recessed deeper into the calliper than others its probably seized or partially seized the remedy is to clean and inspect the pistons, note the pistons are fragile handle them with care and keep any hard or sharp tools away from them. Take a close look and you will see a line of grime where the pistons have extended, clean that line of grime off with a bucket of soapy water and an old tooth brush. Once clean give them a goodly spray of brake cleaner, inspect for signs of wear or damage and then and they should slide in and out easily. It’s not necessary to remove the reservoir lid but is good practice because it releases the back pressure making the pistons easier to slide and eliminates the need for the use of special tools or makeshift socket arrangements. Note if the pistons cannot be depressed by hand there is something wrong somewhere, besides if your doing a proper job you’ll need to remove the lid to inspect the brake fluid. Take care not to extend the pistons beyond the seals, once the pistons are moving freely, assuming the seals aren’t leaking any brake fluid and there is no damage or wear, there should be no need for any further servicing of the callipers.

Discs - 14k miles is nothing in terms of normal wear and tear. Inspect the discs for any excessive wear, warping or scoring. Measure the disc thickness and compare to manufacturers specification. Only replace if there are physical signs of wear or damage.

Brake fluid - Bleed off some fluid at the calliper, this is where you need the reservoir cap off, if the fluid drained out is not a similar colour to the fresh fluid going in then flush the brake fluid by bleeding it through from the reservoir to the caliper until fresh fluid appears.

Veru helpful advice. I have no clue how I could rotate the pistons to clean the hard to reach sides. Also, I would struggle to push them down with my hands alone I had to use a wood clamp (rubber ends) to push the pistons in place. Only brake cleaner was used to clean, or rather, what I was able to clean.

Are you saying I should bleed the brake fluid from the caliper directly?How do I know I bled it sufficiently? I could just play it safe and change the fluid all over, it’s been 14 months since I have done so.

You use a 90 degree angled tool that opens when you squeeze (don’t know technical term). It’s the one that has two little points circlips.

Stick it inside piston, squeeze to open until tool grips inside of piston and you can then rotate piston. Sounds easier than it is though and again, Matt at omc had to help me multiple times

As NT says, when playing with brakes, best to leave it to a professional. I had one looking out for me when I did mine.

You use a 90 degree angled tool that opens when you squeeze (don't know technical term).

I used sth like this in those days… Again, seems like there’s always something else out there to make the job a bit easier

Are the clamps soft enough not to damage the piston? I can’t tell from the pictures

I got no idea…NNever used them but logic dictates if circlip pliers are ok, these will be too. Just don’t touch the outer surface of the piston. 

However I’ll say it again. Best to have someone nearby that knows what they’re doing or can fix any fuck up. The last thing you need is screwing something up on the brakes that you only discover at 70mph…

[quote] I used sth like this in those days... Again, seems like there's always something else out there to make the job a bit easier --- Serrisan [/quote]

Are the clamps soft enough not to damage the piston? I can’t tell from the pictures

CBR500R commuter
generally if the material that's clamping is softer it wont damage the harder face 

a little thig I do before cleaning the calipers is to pump the pistons out a little so you can see the clean edge area of the piston


If any tools used are used inside the piston any pitting or scoring left behind will be of no consequence, do not use any tooling to grip the outside of the piston. With the reservoir cap removed and the pistons extended by gentle applying brake pressure you should be able to rotate the pistons by hand. The trick here is to slowly extend the pistons until you see clean shiny piston behind the ring of grime being careful not to fully eject the piston. I’ve rarely come across a calliper piston that wouldn’t rotate and the ones I’ve had problems with I’ve used angled nose pliers to grip the inside of the piston, once you get a little movement they will rotate easy. The problem is always that the ring of grime is fouling against the dust seal, the most likely cause for this is that in the past some monkey boy has pushed the dirty pistons back using brute force and ignorance forcing the ring of grime past the dust seal. This is why the pistons need to be cleaned when replacing the pads, force that ring of grime past the dust seal and you’re guaranteed a seized or partially seized piston waiting to happen. Note the seizing is always between the ring of grime and the dust seal or worse the fluid seal.

Bleeding the brakes - Many manufacturers recommend to completely drain the brake system and then re-fill it from empty. I recommend to drain and re-fill in one operation by flushing, bleed the system at the calliper bleed nipple, keeping an eye on the fluid level and topping up the reservoir with fresh fluid as you bleed off the old fluid. When fresh clean fluid flows out the bleed nipple the job is complete.

So I spent a few hours yesterday working on the brakes. Following NT’s advice I thoroughly cleaned all 8 pistons to the point that 7 of them were moving freely when applying brakes and I could push them back in using my fingers. Huge difference in performance. 

This weekend i will have to change the brake fluid and probably release the stubborn piston and see what can be done there. Any guidance on removing a piston, cleaning and re-inserting it? or do I have to get a new one altogether?

clamp the two free moving opposing pistion s in place with a lump of wood and then just try to pump out the stuck one 

I usually use a grease gun to pump mine out if I get a stuck piston 

Providing you and any previous fettlers have taken care in the cleaning process it is very unlikely you’d need to replace a calliper piston. Keep at it, as above a piece of wood to hold the free pistons in and gently pump the brake to extend the stubborn one. Once extended carefully clean it as before. The only reason for the piston to seize is that the ring of grime gets past the dust seal which then prevents it from extending. Hopefully its not been left for so long that the dust seal fails, if that is the case you’ll have to drain the system, remove the pistons and fit new seals. At the point of replacing the seals some would recommend new pistons too but if they are not damaged there really should be no need.

I held all pistons in place to push out the stuck one. I extended it as far as I’m comfortable with without risking dislodging it. This is why I am prepared to change all the fluid and clean the piston deep down. Just need to figure out how to do this