Front brake anchored on

[Fred3606]

Hello,
A month ago or so I was changing brake pads. Front seemed fine so I didn't replace. After putting it back together the brakes were spongy so I bled them. They went sponges once more a bit later so I bled them again. They were fine for a few weeks, then after leaving the bike for the weekend I have found the front brake anchored on and hard! I cannot move the front wheel.
I didn't notice it being sticky before. What should I do next?
Any help is appreciated, thanks
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[Itchy]

Dirt got into the pistol seals and therefore prevent the smooth in and out movement of the brake pistons. Therefore the brake pressure pushes the pistons and the pads out squeezing the disc.

But when the pressure is removed they can't move back in to allow free movement of the brake disc and wheel attached to it.


You need to clean your brake pistons.

This means taking the brake calliper off the forks.

Then either:

Pumping the brake lever so the pistons pop out.

Or pumping the brake lever so the pistons come out enough so you can clean the pistons where dirt is preventing pistons from retracting.

The job isn't difficult but increases with difficulty the more brake pistons there are per calliper.

A sliding brake system with two pistons per brake disc is easy and you need no special tools as you can simply use the brake pressure to push out the pistons.

Piston removal tools make the job much much easier.

It will leak brake fluid which is corrosive once you pop the pistons so wear eye protection.

Once the pistons are out you need to clean them and replace the seals (YMMV as I've put them back in more than a few times). You need to remove any burrs which may tear the seals (I used a plastic ruler and finger nails as it's softer than the steel the pistons are made from).

Then push the pistons back in. Others like to fill the calliper with brake fluid then push the piston back in with thumbs.

Then you need to bleed the system to get the air out.
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Spain 2008France 2007Big one 2009 We all die. The goal isn't to live forever, the goal is to create something that will. In the end, your life will flash before your eyes. Make sure it is worth watching.

[natefz6]

My pads seemed to be jammed the other day but I think that it was just the result of some slight rust binding the pad to the disc after a particularly salty shitty ride.

It took a good yank to get it free but once released they have been fine and the wheel spins freely.

Maybe totally unrealated to your problem
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"no I didn't steal it that's just the way I ride"

[AndyCF]

Another cause for this is a dodgy brake hose.

They can collapse internally so they almost act as a 'one way valve' , this means the pressure goes on but does not appear to come off again.

After a bit of time (usually) however it will release again...

[Fisty]

Have you over filled the reservoir?
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Quietly and consistently taking the piss.
TL1000R | Hayabusa | ZXR400 | TL1000S | Bandit 400 V
Fatter and faster than Fret

[kgm]

I'd go with itchy's assessment. Possibly worsened by rust on the pads/disks

[Fred3606]

Thanks for all the responses,
I didn't actually add any brake fluid when bleeding and the level looks about right, so I don't think the reservoir is overfilled.
I've just tried to move the front wheel and with a bit of effort it moves. I tried poking the pad back and the wheel moved a little more freely but after pumping the brake leaver it gripped on once more.
My plan is to remove the calliper over the weekend, pop out the piston and try to clean it.
Can anyone suggest any amendments, extra checks? Also, what will I need? I am assuming it will drain the system, will 300ml of brake fluid be enough? Do I need a special grease for the piston.
By the way it's a 07 varadero 125
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[Pete.]

Blocked return port in the master cylinder. It's a tiny drilling you can see in the floor of the reservoir sometimes covered by a little metal clip to stop the oil squirting out. When you let go of the lever it allows excess oil to flow back to prevent heat from using the brakes building up pressure. If this port is blocked you go for a ride then the brakes start dragging until suddenly they are on solid.

Can also be a sticky lever or master cylinder piston causing the plunger to not fully retract, especially if it's been ridden through winter.
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a.k.a 'Geri'

132.9mph off and walked away. Gear is good, gear is good, gear is very very good

[wots]

I had this happen to me, but it was not the brake system at all, it was in fact my cheap chinese lever jamming. Have you got anything like this? Most likely one of the above suggestions, but worth checking.
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Currently: Yamaha DT 125 LC2,Repsol Fireblade, and Bumblebee MSX 125

[Fred3606]

Ok, interresting. How could I check these. I am assuming that I could just poke the return port.
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[Pete.]

[Fred3606]

Right, taken me a while to have a look due to the rain.
Took the brake caliper off and started to pop the Pistons out.
It's a two piston system and I managed to move the Pistons down low together and one of them popped out but I cannot get the other out by hand. Should I just use some pliers to get it out or could i damage the surface.
It seems the Pistons are fairly corroded around the rim could this be the cause? Could I just clean them, sand them down to the metal and with a bit of red grease pop them back in?
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[Fred3606]

more pics
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[Itchy]

Try clean them up using a piece of plastic or anything softer than the steel of the piston. You want to get it looking similar to the closed end of the piston. Do not use sand paper, do not use a screw driver as you may scratch the piston or cause burrs. Use something soft to clean it and use brake fluid to clean it. The worst that stuff will be is rust but most likely it's road salt.


If you got one piston out then to get the other one you can do one of two things.

1 Clean up the piston that is currently out and change the seals. Then pop it back in so it is flush with the calliper body. Make sure you also clean the grooves the seals sit in too.

You then need to bleed the system completely and HOLD in the cleaned piston so the brake fluid pressure can only act on the other piston.

When you hold it in the pressure will be applied at the point of least resistance the piston you're not holding in and it will pop.

Then clean that one out the same as before then pop it back in and re-bleed the system.

2 Buy a brake piston remover kit. #1 is obviously cheaper but more time consuming as you have to bleed the system twice.
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Spain 2008France 2007Big one 2009 We all die. The goal isn't to live forever, the goal is to create something that will. In the end, your life will flash before your eyes. Make sure it is worth watching.

[Rogerborg]

Definitely do not just just wrap a load of rag around the stuck piston, clamp some grips on the very top edge of it, get it turning to unstick it and then have it out in seconds. Even though if you do slightly mark it, it'll be in the area above the fluid seal even with the piston pushed fully in.

I've certainly never done that rather than fanny about for ages, and if I had, I would have died three times and not been able to tell the tale.
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[Kickstart]

Hi

Not 100% looking at the pics, but that looks like pretty severe corrosion on the piston you have out.

Air line is the easiest way to get the piston out, but watch out for high speed flying pistons.

Failing that carefully use pliers wrapped in something to pull the piston out (rubber cut from a old inner tube for example). But get it wrong you will trash the pistons (quite easily).

All the best

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

[pompousporcup...]

i purchased this once upon a time. 9/10 times it has got the piston out

https://www.demon-tweeks.co.uk/Product.do?method=view&n=678&p=344552&d=124&c=4&l=2&utm_source=Google&utm_medium=Base&utm_campaign=Hand%20Tools&gclid=Cj0KEQjwhpnGBRDKpY-My9rdutABEiQAWNcslEmeR-XDbMca8CxA5E-_UW-Fhs6BNoJLs7Wh71cCAjIaAiub8P8HAQ

[Commuter_Tim]

[wots]

[Fred3606]

Sorry this is a bit late, forgot

Thanks to everyone for your assistance

In the end I bought some red grease and brake fluid on the interbob, popped out Pistons (used pliers for the second one).
For those who guessed it was just gritty salty stuff so I scratched it off with a credit card and cleaned it out. Works brilliantly now
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