Mini Hydraulic liquid press

[Cookiemonster...]

Sorry if the title doesn’t make sense. I have a seized piston on a rear brake calliper and putting it back on the bike and pressing on the rear brake pedal isn’t an option. But the a fluid braking system makes use of he principle of hydraulics and force/pressure.
I have never heard of such a thing but I cannot see why something similar hand held cannot exist where you connect to the caliper and with some fluid press on the device lever to push the small piston in the device (like a master cylinder).
People have even put up YouTube videos with grease guns so almost there ! But grease is a pain to clean and I need liquid instead.
Any ideas?

No. Mole grips and brake cleaner have led nowhere sadly.

[MarJay]

Or... buy a second hand master cylinder for pennies. You can get brand new chinese pitbike ones for a few quid.
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British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.

[G]

Errr... As per Marjay - it's called a brake lever?
Readily available for not much at all.
Designed specifically to push a brake piston out!

[Cookiemonster...]

What a clever suggestion lads thank you!
G I think I can just bypass the brake lever and just pump the master cyclinder manually.
One thing though. I will obviously need to get the brake hose too and connect the master cylinder to caliper.
Are all brake hoses banjo bolts the same standard size for either end so it doesn’t matter what master cylinder nor what hose I get?

[MarJay]

[Cookiemonster...]

Yeah I've got the hose for the bike it came from so no issues, sorry for that pointless question.

I've been putting this off for so long because I really hate brake fluid and mess. Currently the whole master cylinder, hose and caliper system is totally dry and drained of its brake fluid.
If I could use water for now as the fluid to get the system out- no gloves, no special area, no toxic liquid substance especially right now in the dark and cold outside- it would be so so much easier.
I could get started and get over the excuses, but can I do it with water then drain the system then fill with brake fluid tomorrow morning when setting up on the bike tomorrow morning. Or will that wreak havoc on the system if there's a little bit of water in it and it mixes with the brake fluid tomorrow? (unless there's a way to completely dry it out even the inside of the hose which I can't get into because of the eyelets on both ends and not actual access.)

[Kawasaki Jimbo]

Slide hammer piston removal kit.

[Cookiemonster...]

damn, another clever idea- this piston is dead anyway, what do I have to lose luckily I have something like that but I didn't think of it.

[virus]

If you dont understand that brake master cylinders are brake master cylinders, nor understand that putting water in a brake system at any time is a bad idea then I suggest you dont work on brake systems.

top tip, google the word 'hygroscopic'.
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own: 81 xs1100g...
owned: 85 rat CG (sold), 91 GS500e (stolen), 84 gsx400f (scrapped), 81 z250 (siezed, siezed, scrapped), 83 cb250rs (sold), 84 gpz750r ratfighter (killed) 84gpz400 (sold), '80 cb650 ratfighter (wrote off) 95gsx6/12f ratfighter (killed) 91 xj900 (sold)
stinkwheel Well I just had my hands up a pigs fanny. Which makes your concerns pale into insignificance.

[bladerunner]

yup don't use water!!! and if you have left the system dry for any length of time then I'd be worried the seals in the system may dry out and become damaged anyhow.
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Current bikes...cbr929, KDX200's, Rd125lc mk2, RGV250's

[bikenut]

You can use water, hot water, but not how you suggest.

Refit caliper and hose to bike. The hose will allow the caliper to reach a bucket of very hot water I am sure.

With the system containing fluid being pumped, with the caliper placed in the very hot water and expanding like mad, pump away and watch the piston move. If its possible, pump the piston right out.

Then, removed from water and dry all wetted components within 5 minutes. You could dry off and then cover with fluid, then examine and go from there.

Then you can examine the piston ( corroded and deeply pitted no doubt ) and caliper bore. The area between the hydraulic seal and outer dust boot will be corroded and also pitted no doubt, the probable cause of the piston sticking badly and "siezing".

I assume the caliper has just one piston ??

If it has 2 or more, same principle but do not let the other pistons come out at all. Use g clamp or similar to keep them in place.

"Excersize" one piston at a time, pump out as much as you dare, lube and g clamp back in, repeat until piston is "free", Repeat with all the others. When all pistons are free, strip down. Give your self the time to do all pistons in the same "session", do not leave wetted with water and come back to it a week later!!!!!!!!

post some pics......do you have a compressor?
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nuts about bikes

[Robby]

To answer the original question, if the rear master cylinder can't be used then just connect it up to the front brake and pump it out there. It helps to pour some brake fluid into the caliper before putting in the banjo bolt, takes less time to bleed the air up the line then.

Otherwise, as it looks like you have now realised, the best thing to pump out a brake piston is the existing brake system. If the caliper is so seized that it can't be pumped out, buy another caliper.

As for water, whilst you can technically use it, it means stripping and cleaning the whole system afterwards to get it dry, then flushing through with brake fluid, then doing another brake fluid change after a week or so. Use brake fluid and buy some gloves. The Ed China tigergrip gloves are surprisingly good, they last all day.

[Cookiemonster...]

Reverse bleeding fail.
I was reading stuff about people pumping brake fluid starting at the caliper up to the master cylinder and the fluid reservoir using a syringe- because it is so much quicker apparently .

All I see is total mess and brake fluid everywhere.
If the bleed nipple was closed then obviously nothing was going through so I kept it open slightly and pushed the syringe but then there was a resistance no fluid was going through any further past the banjo at the caliper. So I opened the banjo bolt slighty and pushed the syringe again- fluid squirted out from the under the washer at the banjo bolt.

I then turned the banjo ring (is this the correct name?) over so that the neck coming from the banjo ring was going down so it could flow down. Did the same as the above with the neck going down instead of up (was going up in the previous paragraph). No luck.


What am I supposed to do? Why won't the fluid just flow up past the banjo bolt up the hose? What could be going wrong?

[Robby]

Reverse bleeding can be messy. I don't bother.

Put it all together and tighten up everything that needs to be tightened up. Take the lid off the master cylinder and top it up with brake fluid.

Make tea.

Sit there, drinking tea, pumping the brake level, for 5 minutes. Vary your strokes. Air will bubble up into the master cylinder, this is bleeding out the air. This is the easiest and cleanest way of bleeding brakes, but not the fastest. The lever will gradually firm up.

There will still be a tiny air pocket under the bleed nipple on the caliper, but it is tiny and can probably be left alone for the purposes of this experiment. All you're looking to do is pump out the piston anyway.

[Cookiemonster...]

Pre filling the caliper with fluid to the top flush with where the banjo ring would sit and pre filling the master cylinder to the top flush with where the ring on the other end would sit as well as filling the resevoir makes the amount of air so tiny- don't know where I saw that advice about a year ago but it's worked miraculously ever since as well as now.

However getting fluid back into the system with no air still didn't work. Piston still seized. So I drained the system again
And resorted to grease gun. Worked beautifully. Need to jet wash grease out now and get new piston after the abuse it's received. It's ok the whole caliper is getting rebuilt so the water is fine at this point.
Yes I know what hygroscopic means already and that brake fluid is that exactly. That's why I asked if it would be ok if I got rid of the water.

At one point I even tried dremeling a notch and hitting with flathead to shimmy it around and out. I'll edit and post some pics in a bit.

I don't want to spend much money on a single piston but a rear piston set costs 20 quid. A brake disc piston is just a cylinder with an open top after all- is there a resourceful way I can get the exact size and get something that will do the job for like a fiver?

[kramdra]

What the shitting fuck are you doing?!?!?

A used rear calliper and master assembly, with hose and good piston and as-new pads, can be under 30 quid delivered. This is what I'd suggest. What bike is it?

A master cylinder makes a shit hydraulic pump for piston removal, the displacement volume is too low combined with the non-valved ports, prevent building pressure on multiple stokes. No good for tokico 6 pots..

https://www.ebay.co.uk/itm/273630490371 This would do it, but expensive.

[Pete.]

If the whole system is being flushed and cleaned there's no harm in using water, most people don;t realise how far they are injection it into their system when they get turn the jetwash on their bike but cooking oil will do just as well to pump out a stuck piston and it's cheap, easy to get and totally non-harmful.

2/10 for trashing the piston must try harder
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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

[Cookiemonster...]

Yes the piston was total butchery wasnt it?
2/10 is a bit too generous rating imo.

The piston was so stuck a perfectly bled system with brake fluid was doing nothing. Plus it was dead anyway from past attempts I just thought fuck it.

[Cookiemonster...]

[kramdra]

[Cookiemonster...]

[kramdra]

Yes. This could remove any stuck piston, or blow the calliper apart if it cant.

[Cookiemonster...]

All the cheap ones seem to be sold out everywhere now cheapest I can find is roughly £100. Not that I need it right now- just seems like a useful tool if can be found cheap.

[bikenut]

So your moaning about the price fluid and of a piston, you know you will need new seals also.

How is the tiny recouperating port in the master cylinder, blocked????

Think about a master cylinder kit also, or a new one sometimes makes more sense and economy.

I hope the e bay caliper is servicable ???

You now know what is meant by a "liquid lever".

When you hit the cart in front cos your brakes don't work, just make sure its not a red mondeo will you please !!!
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nuts about bikes