Brake caliper piston; renewal

[ginge191]

Reading around removing the piston and people have removed them whilst they've been on the car which is all well and good. I'm looking at removing the pistons when off the vehicle?

Has anyone got any tips to getting the piston out?

ALSO has anyone got any tips to refitting the piston as all i ever here is it's a pain in the ass...

I'm planning and in the middle of writing a caliper refurb guide - sliders etc are fine

[Toms306]

Air pressure with some sort of foot/hand pump through the hose should push the piston out. Obviously with the bleed nipple closed.

[ginge191]

Air pressure with some sort of foot/hand pump through the hose should push the piston out.  Obviously with the bleed nipple closed.

sounds dumb... but how am i sealing the pump into the 'brake inlet' - surely it won't seal to build up enough pressure as the ID of the brake inlet is larger than the OD of the pump nozzle?

[Toms306]

The right size nozzle would be an advantage lol, if not, some tape around a smaller one should work, you wont need tonnes of pressure.

[Connor]

Workshop compressor, air blower, job jobbed

[ginge191]

Workshop compressor, air blower, job jobbed

Asshole

Cheers Tom, will have have a play around once i know whether or not to change the seals...

[pug306driver]

I presume front caliper pistons??

if they are seized solid ( difficult to imagine on a car with servo ) or very stiff, do not disconnect the hydraulics yet.

use the hydraulics to your advantage...............peel back the boot ( piston boot or gaiter ) and lub piston with brake fluid, then with an assistant pumping the brakes ( with caliper swung off the disc etc ) and with good communication, pump out the piston as far as you dare without it coming out completely ( so that you still have hydraulics to help you ) ....they using a g clamp and wood to protect the caliper and piston, gently force the piston back in ( excersising the piston) .

if very stiff use a heat gun (hot air ) to help.  sometimes I place the caliper assembly in a bucket of boiling water ( kettle full ) to heat caliper and piston as a whole and then excerside the piston.  once free, pop the piston out and disconnect the hydraulics.  the "land " between the caliper hydraulic seal and the outer gaiter usually corrodes, as well as the piston, to make the piston very stiff and not self release ( piston pulled back due to hydraulic seal acting as a spring ( seal deforms when piston is pushed out via the fluid and then un deforms back to original shape, taking the piston back with it ) .

use red rubber grease for reassembly of the piston and hydraulic seals etc.  piston should be a thumb pressure to push back in with the m/cylinder cap off..........

rears  are a bit more involved as the pistons need to be wound back in so need to turn or rotate.

remove the bleed nipples on the bench with the seals removed as heat can be applied...........do not shear them off!!!

when clean and painted ( golden opportunity here ) reassemble, fit and bleed.

deal with one side at a time, and make a "brake union blocking device" to block the metal pipe union or complete fluid loss,one that screws into the union on the metal pipe.........else total fluid loss and system will need total bleeding ( other bleed nipple problems etc )

[ginge191]

I presume front caliper pistons??

if they are seized solid ( difficult to imagine on a car with servo ) or very stiff, do not disconnect the hydraulics yet.

use the hydraulics to your advantage...............peel back the boot ( piston boot or gaiter ) and lub piston with brake fluid, then with an assistant pumping the brakes ( with caliper swung off the disc etc ) and with good communication, pump out the piston as far as you dare without it coming out completely ( so that you still have hydraulics to help you ) ....they using a g clamp and wood to protect the caliper and piston, gently force the piston back in ( excersising the piston) .

if very stiff use a heat gun (hot air ) to help.  sometimes I place the caliper assembly in a bucket of boiling water ( kettle full ) to heat caliper and piston as a whole and then excerside the piston.  once free, pop the piston out and disconnect the hydraulics.  the "land " between the caliper hydraulic seal and the outer gaiter usually corrodes, as well as the piston, to make the piston very stiff and not self release ( piston pulled back due to hydraulic seal acting as a spring ( seal deforms when piston is pushed out via the fluid and then un deforms back to original shape, taking the piston back with it ) .

use red rubber grease for reassembly of the piston and hydraulic seals etc.  piston should be a thumb pressure to push back in with the m/cylinder cap off..........

rears  are a bit more involved as the pistons need to be wound back in so need to turn or rotate.

remove the bleed nipples on the bench with the seals removed as heat can be applied...........do not shear them off!!!

Yes it's the front calipers.

The calipers are already off the vehicle and compressed. Bought them online. The sliders came out freely and the cm of the piston protruding went back in fine; so they're not seized.

I'll have a think as to whether i'll refurb the pistons or not.. as the new piston kits aren't that cheap.

Thanks for the information!

[pug306driver]

picks of pistons, any pitting or corrosion etc??

since they are free, codge an air pump but watch fingers as trapped by a piston bloody hurts so I'm told!!!

very embarrassing walking into casualty with a caliper hanging off your finger with a squiffffff jammed piston etc.....

[Jonny81191]

Workshop compressor, air blower, job jobbed

Asshole

Cheers Tom, will have have a play around once i know whether or not to change the seals...

Why does that make him an asshole? Just go down the local garage and ask them nicely, might cost you a few quid or some beers.

[welshpug]

be very careful with compressed air, theres far more force behind it because it compresses so much, better to use hydraulic force if at all possible, then you won't have a projectile.

an m10 bleed nipple screwed into the fluid port gives a good way to connect a hose, obviously not fully home as it may seal.

tbh, if you really have to ask should you really be writing a guide?!

saying that, just pin this topic as it now has the info you need :p

[ginge191]

tbh, if you really have to ask should you really be writing a guide?!

Why do you say this? The technical aspects; ie replacing seals and the understanding of how to refurbish the caliper isn't the issue, it's removing and replacing the main piston? And whether anyone had any tips on this?

I wrote up a 'how to' changing front struts to coil-overs/spring change, never did that before, and in my opinion had been repped and commended a few times.

It was more to help others as the community often provides "how to" threads, seeing as this hadn't been covered I thought i'd take it upon myself to help out. BUT not to worry, im sure someone who has refurbed calipers and has no questions or queries (and likely no want to post a 'how to') will be able to continue to answer the questions in the future

[nominous]

A few ideas...

This might not work for the pugs it wouldn't have worked for the passat I was working on at the weekend either, but I'll get to that.
For the hondas the brake line is banjo'd to the calliper.
So if replacing a piston it's put a drift through the hole and push the piston out.

For the passat I used large pliers on the piston, held the calliper and wiggled it out.

Elsewise if/when that doesn't work, I have a small length of brake line rubber hosed to an old tyre valve with the rubber scraped off it.
Thus can be applied to a foot pump even to push the piston out the calliper. I have a compressor, but I've done it with a 12V mini tyre inflater previously.

[pug306driver]

So if replacing a piston it's put a drift through the hole and push the piston out??????????????

make a special tool, which grips the inside of the caliper piston, the volume of coffee if the piston was a mug, if you get my meaning.....the void inside the piston ( weigh saving etc ) but all caliper pistons will not have this..........

an inside out pair of pliers so your queezing of the pliers causes the "jaws" to expand outwards, thus gripping the "inside" of the caliper piston.  A turn and pull technique.........

will find a pic for those still confused!

do not grip the caliper piston on the outside as this will cause chrome plating damage.....defo do not grip the "hydraulic seal area" unless you are fitting new pistons ( you will have to after buggering the mirror finish seal surface ).......

brakes are safety critical, as you all know.

the fronts are easy but the rears......are much more involved.........

[nominous]

So if replacing a piston it's put a drift through the hole and push the piston out??????????????

As I said, works for the hondas as the hole is exposed to allow it and has a banjo connection. But my passat cannot do that as the hole for the hose is at an angle and a tiny orifice.
Did this many times before I made the tyre inflater thingy.
Incidently the back side of the pistons are often not coated and it's difficult for something to rust when immersed in brake fluid.

do not grip the caliper piston on the outside as this will cause chrome plating damage

The bit not protected by the rubber boot which 9/10 will have rusted ?
I wouldn't worry too much. And then if removing the piston which is found to be ok, I'd tape off the rest of it then wire brush and paint the tip to protect it.


FYI, a new piston for the passat was 9quid delivered from ebay. Faffing around servicing a piston, not worth it IMHO. Buy new piston and seal kit.
A job I've been putting off for ages, when I finally got to it the piston so pitted that the brake fluid was leaking around it, but the seals were intact.

[pug306driver]

i stand corrected....and theres me thinking brake fluid was hygoscopic!

did not the pitted piston damage ( score and/or indent ) the hydraulic seal surface or face??

[nominous]

Weirdly no. The seal was not ripped or damaged. Replaced any way, but the pitting was severe so I'm guessing it was enough that it was passing around it. Anyway, OT.

yeah, it is hygoscopic. But if you've got brake fluid full of water then you have other problems
NB: I said difficult, not impossible...

[306Dan]

For when I'm refurbing I have a selection of old brake flexi's so I can screw them on then apply air down them, most of the time they come out into a rag no probs but sometimes you get ones that turn into a missile so be careful. I usually hold the caliper down to a bench so the piston can't escape and have a few rags in there so it doesn't damage itself.

[ginge191]

Some really handy tips there, thanks! i was probably going to replace the piston also. The old ones are fairly rusty externally, and for peace of mind, i think i'll replace the seals and piston. They come as a kit anyway.

[pug306driver]

Some really handy tips there, thanks! i was probably going to replace the piston also. The old ones are fairly rusty externally, and for peace of mind, i think i'll replace the seals and piston. They come as a kit anyway.

pics pics pics..........