Overhauling brake calipers - Guide

[White Noise]

Thought that I would write a little something to share my experiences of brakes, in particular brake calipers. Having a couple of days free where my bike (ZX-7R) wasn’t ride able due to crash damage I decided that I should take a look at the brakes, in particular the front, as when a friend rode it he said they where a little on the spongy side. My initial plan was to follow Korn's guide on cleaning brakes in addition to bleeding them, and when I got back on the road see if they had got better, so started to clean them (in this case i used carb and clutch cleaner), and boy did they need them as the pistons where black and covered in a thick layer of brake dust! Cleaned the first 6 pot (piston) calliper with no problem with all the pistons moving freely in and out! Jobs a good’un. Then moved onto the second caliper, cleaned four of the pistons fine and found that one pair where stuck (Seized), I blocked the other four pistons from moving with a piece of wood between them and pumped the front brake, one of the stuck pistons began to move, however as it started to come out it was pulling out a dust seal! see picture 1

https://www.bikechatforums.com/download.php?id=30761
Picture 1: caliper - the problem

It may prove worthwhile to give a diagram to show the that what a caliper is made up of to understand whats going on, see diagram 1!

https://www.bikechatforums.com/files/piston_diagram.jpg
diagram 1: Diagram of caliper

I tried to get this piston back in but no luck by hand so I tried doing it with a G-clamp and wood to protect the caliper and the piston, in fact I tightened up the G-clamp so much it snapped (cheap clamp :LOL:)! So with that piston not budging it looked like the dust seal was toast so the caliper could do with an overhaul. I drain the brake fluid from the system with the aid of Davo and an interesting technique!
As I was draining the system I decided to go the whole hog and fit some braided lines, so they got put on order, Stickwheel’s guide gives you some damn good advice here!
With the calipers off and brake fluid drained from them, it was time to get to grips with them, now the first problem when overhaulling the calipers is to get the pistons out of their barrels. The problem here is that you have to find a way to get them out without damaging the outer bore of the piston as this will lead to it damaging the seals when you put the pistons back in there barrels. So DON’T be tempted to use mole grips unless you want headaches later on!
There are a few ways to get the pistons out, but it depends on what facilities that you have available to you. One way is use compressed air attached to the banjo bolt thread and blow, unfortunately the problem is that once that one or more pistons have been removed the air has loads of holes to escape from, hence reducing the pressure acting on the remaining pistons, this can overcome by making a jig to get pistons out one by one, see diagram 2 below.

https://www.bikechatforums.com/files/caliper_jig_179.jpg
diagram 2: diagram of jig

but another way, and in fact the way that I did it was that I found that my usual bike garage has a Motorbike Brake Piston Removing Tool, and they let me use it for free, the only problem is that you have to split the calipers which isn’t bad as long as you don’t loose the rubber seals between the caliper halves! see picture 2

https://www.bikechatforums.com/download.php?id=30762
picture 2: calipers split

Using the tool is easy and I had all 12 pistons out in ten minutes, such a time and pain in the arse saver! Only problem is it costs £90 so unless you are doing loads of calipers its time to find some else with one!
With all the pistons out you can have a good look at the state of the brake pistons oil and dust seals, when I did the same job on the rear caliper of my diversion the dust seals where ripped to shreds, with huge chunks missing! From the inspection of all the 12 dust seals there is only a small nick out of the one side of the rubber and the rest are fine, along with the oil seals, the nick isn’t going to cause too bigger problems so I can live with, but if you are in any doubt get new seals as they don’t cost that much and ask your self the question when am I next going to that the calipers apart? One thing that you have to be careful for when removing the seals it to try not to damage them so take care when you do it! With all the seals out take a look at the seal seats as these can become cogged with crap and corrosion and make the seal not sit properly, and hence not doing its job properly, so you need to get rid of this crud out of the seat. I found that a 3-4 mm allen key did this job well, by running the short head into the seat and scrapping off and the crap from the corners. Do this for the dust and oil seal seats on your calipers. Next take a good look at the pistons that you have taken out and check the outer bore for scuffs, dirt and anything that might damage to the seals, if you find anything that can’t be removed or the surface is corroded you have to replace the piston or it will act like a cheese grater on your seals. Give the piston a good clean both on the inside and out, you want to clean the inside as brake dust may have become deposited there and could cause embarrassing brake squeal after you reassemble the brakes.
Once done the caliper halves needs to be cleaned to get rid of the stuff you have scraped off. I did this in the kitchen sink while my housemates weren’t looking! :LOL:. Dry the halves off and let them dry completely, once dry and if you have got access to compressed air blow down the brake fluid channels to get rid of debris, blowing down them will also do the same job! So with the calipers and seals clean its time to refit every thing, see picture 4

https://www.bikechatforums.com/download.php?id=30764
picture 3: ready for reassembly (oil seals already fitted)

to reasseble sit the seals in there respective seats, if you have a modern bike/caliper be careful as the pistons maybe different diameters, hence different size seals so get them in the right place!
With the seals in place, do a last check that there is no debris in the barrels, if there is just use a cotton bud to clean it out, then with another cotton bud dipped in brake fluid lubricate the seals, then slide the right sized piston back into its barrel. Put the rubber seals between the calipers back into place and bolt the two halves back together at of course the right torque setting!

https://www.bikechatforums.com/download.php?id=30763
Picture 4: caliper - reassembled

Replace the brake pads remembering to use copper slip where they touch the pistons. Reconnect the brake lines and attach the caliper back on the bike, then you can go through and bleed the system with new fluid in the usual way, hopefully after all of that this will provide better braking with the new fluid, a good clean and braided lines if you have fitted them.
This is merely a guide to how I did the job and not a definitive answer on how to do the job, the basics are pretty much the same with all calipers but people will have different methods of removing the pistons, if people could provide there methods that would be great as people have different circumstances to work in.
Anything you think that I have missed or doing something wrong let me know
when i get the bike back on the road next week i will let you know how the brakes feel
WN

Disclaimer: I am not responsible for anything that happens to you if you follow this guide
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Wing Commander White Noise - SE Clique
Riding Tip #86: See God, then back off a bit: Problem is i haven't seen god yet, just a close up of tarmac on revett straight

[Lee_367]

Good guide, Going to clean my calipers up tomorrow, what cleaning stuff is the best?
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[Slinn84]

good guide

just out of interest, you say you snapped a g-clamp when trying to push a piston back in, i had this problem with my rear caliper, one piston pushed in fine but the other would not budge for love nor money

so took it off and just about to overhaul the caliper when i pressed the piston, it slid back in perfectly. seems the back pressure from the old shi@#y fluid was too much but draining the fluid released the pressure and they went back in easily

i have also overhauled my front calipers and found that the easiest way to get the pistons out is to loosen the banjo bolt and use the brake lever to push them all out. you get covered in excess fluid but a few carefully placed towels sorted that out

[White Noise]

[Major_Grooves]

Okay, anyone got any other bright ideas for how to get a brake piston out

I don't have compressed air, or a jog or a piston removing kit. I've tried pliers with protection on the piston but it won't budge.

[kat250]

What kind of caliper is it what i have done is get say a strip of metal. If you have pressure in the system pump the lever until piston pushes against metal hold piston in place and keep working the lever. other piston should come out enough to get hold of it.
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in the famous word of jimmy pop "would you F*ck me for blow"
In the words of banditshigh "would you blow me to f*ck"

[Major_Grooves]

It's a Nissin from a CB500.

The calipers are off the bike. I did what you suggested to get the first one out (2 pistons), but can't get the remaining one out. It's not particuarly jammed as I can use a G clamp to move it back in, but it won't come out of the caliper at all.

[kat250]

What ive done is a set of pliers and cloth on it and tried to twist and pull. But i have seen me screw it up and realy score the pistons. Just a case of realy trying to pull it out.
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in the famous word of jimmy pop "would you F*ck me for blow"
In the words of banditshigh "would you blow me to f*ck"

[Kickstart]

[Major_Grooves]

[element]

[Kickstart]

Hi

Given the pressure that the master cylinder takes when braking I think I would rather the master cylinder fail when pumping a piston out rather than when I am actually braking.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[cliff]

[sickpup]

[White Noise]

[stinkwheel]

Just remember to keep out of the way (put it in a cardboard box) a lump of metal propelled out by 120psi of air pressure will hurt if it hits you.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[White Noise]

[Major_Grooves]

[loply]

I get the pistons out on my calipers by spraying compressed air into the bleed nipple, they pop out in about half a second, really quicky and easy.

If you dont have an air compressor though, then I dont know how you could do it.
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Yamaha SZR660 Caution to the wind, the throttle pinned!

[Major_Grooves]

[White Noise]

[Major_Grooves]

[Davo]

I think White Noise had it clamped in a way that the other piston was almost out but was in far enough for a seal to still be there.

[loply]

The really obvious solution here is to just do them one at a time

Spray the compressed air, when one pops out, clean it. Put it back in, and clamp it there. More compressed air, whichever one pops out, clean that one. Repeat for each piston.

I think thats how I did it, anyway.
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Yamaha SZR660 Caution to the wind, the throttle pinned!

[White Noise]