Seized front brake piston - any tips on how to get out?

I'm rebuilding my front brakes, and have found the piston to be seized in the caliper - no wonder it wasn't braking!! I don't have compressed air in my little garage, so am wondering if anyone has any tips on how to free the piston. TIA.

 

If you are going to replace the seals [which i suggest] give it a good spray with [out here] wd40 or rpg or some type of lubricant and rust anti sieze and let it soak abit , that stuff in the tin , then give it a cupla light "taps" with a device , maybe a hammer , the piston that is , and if can take to to a servo and give it a blow with air too at a last resort , gradually it will unfreeze , just do not mark the surface of where it slides in or out , good hammering .

 

Or i just thought , is put it back together , and leave the caliper off the disk thats froze and bleed brakes and use the brake lever to force it out or at least move it....

 

I will be replacing the seals. I found that it didn't have one of them, perhaps that's why it is seized. I put some rust freeing stuff in there, I'll let it soak overnight and take it to my friend's place where there's an air compressor.

 

I had the same problem, and the only way to get it out was what Hoonz suggested. Hook the brake line from the master cylinder back up to the frozen caliper and pump the brake lever a few times. The piston will pop right out. You may have to add some fluid to the reservoir. It was a little messy, but the only thing that worked for me.

 

Depends on the position it's stuck in. If it is not fully in then you can use a g-clamp and some blocks of wood to avoid damage to squeze it in before using the MC to pump it out.

Once its frred up it will come out easier and put less stress on the MC.

Another option that I have used(depends on thread sizes/fitting etc.) is to screw a grease gun hose in place of the brake line and use greare to pump it out.

 

Could you use some of the nice penatrating oils out there? I have a few cans of stuff I use for removing rusted bolts. As you are rebuilding it afterwards I don't see the harm in using it and it is more effective (I find) at freeing things up than wd40.

Also cover the area with shop towels so that if it does pop out it doesn't get damaged falling or flying... usually I'd stuff rags between the holder and the piston - it can come out then but it can't fly anywhere.

 

Sorry guys, but IMHO using WD40 or penetrating oil is what is dangerous. If you don't get out all the residue, you can be in for a world of hurt as you change the hydraulic properties of the brake fluid and one day find that you can't stop or you press on the brake and it locks up on you. I have seen this way too often and think you are gambling with your bikes and your lives.

If you can't get a piston out by hooking the brake line back up and pumping it out and you don't have compressed air, I would take it to a local shop and have them do it. Yes, it will cost you some money, but better safe than sorry in my opinion.

 

Man, that was a stubborn piston!! Finally got it out with compressed air AND heat applied carefully to the caliper. Didn't want to budge with just compressed air. I'm thinking of putting stainless line on, and was wondering about eliminating the junction fitting that's on the fork mid-point, and just going from the master reservoir straight to the caliper with a hose clamp where the junction used to be. Any thoughts about that??

 

As long as you watch the routing of the cable, you should be fine!

 

There is no need to maintain the splitter log, it's just one more place to leak. I got rid of mine.

 

Thanks, that's what I figure. I'm going to get some stainless line made up when I get my new superbike bars on and see if that improves the braking over stock. Well, any braking would be an improvement over the total lack of braking that the bike had when I bought it!! I discovered that the front brake was seized when I unloaded the bike from my van!

 

I'll guarantee it!

 

A bit late on this thread but another way to remove the piston is to drill a hole though the middle of it, being careful not to drill into the caliper of course. Then tap threads into the hole you have drilled, and turn a bolt into it. It will come out like it's buttered.
Naturally you need a new piston after this so it's really a way of salvaging a caliper.
Jim

 

Whilst i am going to replace the fork seals [LH side leaking] i had a look too.

LH side caliper stuck , RH side ok , so i do both , out here there is a kit [a piston and seals].

This was easy fortunatly, remove the lower lines [if you have antidive] and use the shorter brake line bolt and fill the calipers with brake fluid [if you have removed them to look] and fit the lines , bleed a bit , then just keep using the brake and refilling master cylinder until the pistons are nearly across to the other side [no pads in of course] , if one is moving more than the other put in a wedge [i used a socket bar] between the piston and caliper so it jams that one and moves the other until they move evenly out....

stuck side seals were all mushy and soft even though no leaks , rust on the piston..

 

Also me no mention to reassemble using certified brake rubber grease too and if not confident on reassembly one could dissmantle / clean / get new parts and then take to a workshop to get the dudes to assemble .

Remember its your brakes and sometimes a horn wont help

 

Finally got em , posting if there is a interest.

even came with rubber grease , day all together now , a gentle constant push and they [caliper pistons] slid in easy...., assemble forks tomorrow..

 

Forks on and all worky ok so far [no engine in yet , hopefully next week , pushed da bike against the wall here in the kitchen and tryd da up and down then with brakes and sure did work as no move down at all , engine weight will effect that] , but i wanted to add this , on assembling the brake lines the lower short ones to the antidive were full of crud [soft and hard] in the area of the banjo bolts , in the valley of the fitting and also after putting on 3 power zoom spectarkles the lower bolt had deposits in there too , so after all these years a good check about is suggested...

 

Hi I'm having the same problem with piston stuck in . iv clamped the one to get the other out and then the other one is stuck in. If I use the brake fluid to push them out they meet in the middle and cannot get them out. Am i missing something here.
thanks Paul
tried pliers to pull out , not working.

 

If i understand what you meen is that you want both out together? , still you just keep using the brake lever and juggle each one and the wedge size until they look like to pop out [nearly right to the other side].


if day already moving they have to keep going to pop out...