Seized brake piston

[PaulC]

Evening all, after some adventure with regards to my front brake woes. I bought ant untested complete 400/4 caliper unit, when I picked up a replacemnt frontend.  I've tried various YouTube methods to get the piston out; greasegun etc. Could the actual tube be blocked I.e. where the banjo bolt screws in, as I'm getting fluid through the brake cables. For information: the cables, master cylinder, banjo bolts and bleed nipples are all new. The only thing I haven't tried is heat and the caliper is currently soaking in evaporust - until my patience returns 😀

Thanks in adavance Paul

[Johnwebley]

Is the nipple loose?

You could try bleeding the system,



Then using the master cylinder to pump out the piston.

Or have I got it wrong?

Sent from my SM-A750FN using Tapatalk

[PaulC]

Hi JW,

I primed the brake cable with fluid before fitting it to the caliper, then grasped brake lever but it wouldn't budge. So opened the bleed screw expecting a release of air but the lever still wouldn't budge!

Is the nipple loose?

You could try bleeding the system,



Then using the master cylinder to pump out the piston.

Or have I got it wrong?

Sent from my SM-A750FN using Tapatalk

[K2-K6]

They can get hellishly tight and need alot of effort to initiate moving, as you're finding.

When like that, probably only the hydraulic system will move it with the leverage needed.  The mastercylinder will generate into the hundreds psi wise.

You could try putting a spacer onto the piston and squeezing in a vice to see if you can crack the corrosion sealing it seized, then see if it'll pump out. Sounds counter intuitive, but once moved from fully stuck they'll usually get going.

[K2-K6]

Crossed over there 

If you can unbolt both caliper fitments,  then use thin wire to "winkle" around into the bores to see if you can clear anything obvious.

[McCabe-Thiele (Ted)]

They can get hellishly tight and need alot of effort to initiate moving, as you're finding.

When like that, probably only the hydraulic system will move it with the leverage needed.  The mastercylinder will generate into the hundreds psi wise.

You could try putting a spacer onto the piston and squeezing in a vice to see if you can crack the corrosion sealing it seized, then see if it'll pump out. Sounds counter intuitive, but once moved from fully stuck they'll usually get going.

The above suggested method has worked for me in the past - for stubborn ones in the past  I used an old MIni Clutch Master cylinder to pump the pistons out.

[PaulC]

They can get hellishly tight and need alot of effort to initiate moving, as you're finding.

When like that, probably only the hydraulic system will move it with the leverage needed.  The mastercylinder will generate into the hundreds psi wise.

You could try putting a spacer onto the piston and squeezing in a vice to see if you can crack the corrosion sealing it seized, then see if it'll pump out. Sounds counter intuitive, but once moved from fully stuck they'll usually get going.

Thanks K2 I'll have ago at that tomorrow. Would using heat help?

[K2-K6]

Heat almost certainly won't hinder it and may benefit, there's not much risk and I'd be inclined to heat the caliper in an oven rather than direct with heat scource.

There's essentially nothing inside them, just the piston and seal and they're pretty robust anyway.

[Bryanj]

Ive never had the grease gun fail, but then i do use the air one at work, also you can get a caliper complete with with mounting, bolts, adjuster and pads from amazon for about £66. Put cb 500 caliper into the amazon search but scroll down as there are several and prices vary a lot, if you leave out the bracket i saw one at £51

[PaulC]

Heat almost certainly won't hinder it and may benefit, there's not much risk and I'd be inclined to heat the caliper in an oven rather than direct with heat scource.

There's essentially nothing inside them, just the piston and seal and they're pretty robust anyway.

Best wait until the wife goes to work for that one 😉

[PaulC]

Ive never had the grease gun fail, but then i do use the air one at work, also you can get a caliper complete with with mounting, bolts, adjuster and pads from amazon for about £66. Put cb 500 caliper into the amazon search but scroll down as there are several and prices vary a lot, if you leave out the bracket i saw one at £51

Bryan, if all else fails that'll be my final option

Cheers

[PaulC]

This has never failed for me.

Get the caliper, turn it upside down, flat side down. Now get a 10mm drill and drill a bloody big hole in the dome section, get a 10mm bolt and just drive that bad boy piston right out of there. Now you say, that's left a big hole in my caliper but fear not intrepid adventurer the solution is at hand.

Get an old style sixpence and just braze that over the hole. In case it leaks then just braze a old style penny over that, if that leaks then I'm sorry but I can't help you, you're just crap at brazing.

This advice of course only works if you have a handy supply of old style currency, don't try this at home kids.

I had considered drilling and tapping the piston or trying to weld a bolt to it. Unfortunately I'm all out of old coins and my brazing is worse than my welding 😀

[Moorey]

     If you can't get it out with a good grease gun then I would think the oil ways in the caliper are solid and must be cleared first. A good
     high pressure grease gun should be able to do 1000bar which is far far higher than the pressure generated in a braking system.
     We used grease guns at the pit on hydraulic nuts and locked them off at just under 1000bar.

[PaulC]

     If you can't get it out with a good grease gun then I would think the oil ways in the caliper are solid and must be cleared first. A good
     high pressure grease gun should be able to do 1000bar which is far far higher than the pressure generated in a braking system.
     We used grease guns at the pit on hydraulic nuts and locked them off at just under 1000bar.

Moorey, that's exactly my thoughts, so I got the Dremel out with a fine bit and that sorted it.  Thanks everyone for your advice and comments. The caliper is now sat in evaporust overnight and I'll check it's condition tomorrow. I also drilled a small hole in the piston so I could free it with a drift, which worked a treat.

[PaulC]

This is the end result: