Front Brake caliper Piston Stuck??

[Steve 940]

Hi Mark,

I do have one of those trim removal sets, and that had a couple of pretty substantial plastic levers that I can use perhaps to lever it out, will see tomorrow if ATF/acetone has worked its magic.

I have looked at the various parts to rebuild calipers, and was going to see what the bores were like first before I buy all pistons and seals etc, as if they're shot then it'll be new calipers.

Cheers
Steve

[griston64]

Originally Posted by Steve 940

Hi Mark,

I do have one of those trim removal sets, and that had a couple of pretty substantial plastic levers that I can use perhaps to lever it out, will see tomorrow if ATF/acetone has worked its magic.

I have looked at the various parts to rebuild calipers, and was going to see what the bores were like first before I buy all pistons and seals etc, as if they're shot then it'll be new calipers.

Cheers
Steve

If they are really stuck the plastic will break before they come out. I found ( as Dave suggested ) if you push them in then lever up gently a few times to loosen it will be easier than just trying to lever out in one go. You want a fairly meaty headed flat screwdriver and make sure they are both the same length. Rest on an old slider pin to give you more leverage

[jasons]

try heating up the caliper body with a blow torch, I heat from behind/opposite side to piston, then as it cools and is just safe to touch try 10bar air pressure.

If the piston is far enough out to get some grips round it you can try twisting it.

So far one has never beat me.

Good luck

[Steve 940]

Hi Jason,

Many thanks for the suggestions, most appreciated, always good to have more options.

My large grips had indeed come into mind, but thought better to seek more experienced opinions from this forum. Weathers a bit grim today, but might get out to the garage to see if it will budge.

With the heat method, certainly something I hadn't thought of, obviously calipers are fairly used to heat, but I assume you just have to be a bit careful not to get it so hot that it melts the piston seal?

Glad to hear you haven't been beaten by one of these before, fingers crossed👍
Cheers
Steve

[Laird Scooby]

Originally Posted by Steve 940

Hi Jason,

Many thanks for the suggestions, most appreciated, always good to have more options.

My large grips had indeed come into mind, but thought better to seek more experienced opinions from this forum. Weathers a bit grim today, but might get out to the garage to see if it will budge.

With the heat method, certainly something I hadn't thought of, obviously calipers are fairly used to heat, but I assume you just have to be a bit careful not to get it so hot that it melts the piston seal?

Glad to hear you haven't been beaten by one of these before, fingers crossed👍
Cheers
Steve

As you'll no doubt be renewing the piston seal Steve, you could consider the existing one as sacrificial if it gets the piston out. Don't touch the melted/burned piston seal without disposable gloves though, once heated they release some nasty stuff, can't remember just now if it's poisonous or carcinogenic but either way you don't want it near you without protection!

[Steve 940]

Yay, success!!!

Dave's first suggestion of pressing in, worked first time👍👍

After pressing piston in a few mmm, tried my little 25 ltr 8 bar air compressor using the blow gun, with rubber protecting hose union threads, piston came out a dream.

Oh, top tip, I had taken precaution of using reducing thicknesses of scrap wood to protect the piston as I was aware it may come out with some force. Certainly did, you wouldn't want fingers in the way!!!!

Also just need to be a bit careful using this method, as the old fluid in the caliper did squirt out as I couldn't get a 100% air tight seal, perhaps make sure goggles on.

Piston looks in good shape, caliper now back in electrolysis tank to see what we've got. Not sure if saveable, as it did feel as though there was a slight ridge around 10mm up from the bottom of the bore, may be just general crud🤞

Any tips for removing the seal without damaging the caliper?? Also any tips on assessing caliper for wear etc once I get it out of the electrolysis tank?

Cheers
Steve

[Laird Scooby]

Originally Posted by Steve 940

Yay, success!!!

Dave's first suggestion of pressing in, worked first time👍👍

After pressing piston in a few mmm, tried my little 25 ltr 8 bar air compressor using the blow gun, with rubber protecting hose union threads, piston came out a dream.

Oh, top tip, I had taken precaution of using reducing thicknesses of scrap wood to protect the piston as I was aware it may come out with some force. Certainly did, you wouldn't want fingers in the way!!!!

Also just need to be a bit careful using this method, as the old fluid in the caliper did squirt out as I couldn't get a 100% air tight seal, perhaps make sure goggles on.

Piston looks in good shape, caliper now back in electrolysis tank to see what we've got. Not sure if saveable, as it did feel as though there was a slight ridge around 10mm up from the bottom of the bore, may be just general crud🤞

Any tips for removing the seal without damaging the caliper?? Also any tips on assessing caliper for wear etc once I get it out of the electrolysis tank?

Cheers
Steve

If you use a cotton polishing drum in a drill and some Halfords rubbing compound on it, you can polish and remove the ridge in the piston bore. From everything that's gone so far, i'd suggest the ridge is simply dirt that has formed round the forward edge of the seal and until you moved the piston in there wasn't enough momentum behind the piston when trying to eject it with compressed air.

https://www.halfords.com/motoring/pa...in%20a%20jiffy.

I believe (although not 100% sure) it's what is known as a "diminishing abrasive" - in other words it starts off coarse and as it's used, the particles reduce in size so the longer it's used, the finer the finish. Obviously there's a point where it's removed enough plating that if any more is removed there will be no plating but you'll have achieved a near-mirror finish long before then unless corrosion has pitted the piston and/or caliper bore.

Don't forget to wash any excess compound out once done, any remaining abrasive will wreak havoc with new seals!

I normally use acetone or IPA as both are good degreasers/cleaners/solvents.

I'd add the piston to the electrolysis tank as well, it probably didn't get much first time round unless you deliberately added a wire link to the piston so it became an electrode. You may be pleasantly surprised at the result of adding the piston!

Also don't forget to bake the caliper and piston in the oven for an hour or so to aid removal of the hydrogen from them to avoid hydrogen embrittlement. Most things you can get away with and just let them naturally degas before painting with no long term effects from the hydrogen but with suspension, brake and steering components, i'd definitely give them an hour or so at ~100C to help get the hydrogen out quickly.

Once it's all clean and dry with any remaining dirt removed, you can assess the condition and go from there.

[Steve 940]

Cheers Dave,

Yes I'll just have to wait to see how they come out of the de-rusting, the piston is in as well as the caliper.

Very good point about the oven, I had read about need to degas after electrolysis, particularly on a critical item such as brakes.

Might need to do this job when SWMBO is out!!!!😀

Cheers
Steve

[Steve 940]

Caliper Refurb Latest Update

Hi, been a little distracted from this project over the last couple of weeks with other gather more pressing 940 'issues', the joys of older Volvoing just keep giving

Managed to get calipers all apart but stainless clip in the man caliper body was seriously corroded in place on both.

First go with electrolysis was a rather Heath Robinson affair with a 10 litre plastic paint tub with various scrap pieces of re-bar, odd bits of steel scrap as anodes spaced around the edge, all wired together in series to positive. Wired caliper to negative and suspended in solution on a wooden stick, making sure not touching the anodes.

Worked ok after a day or so, but looking online, the process seems only to work on line of sight to anodes. The amount and depth of rubbish on the calipers caused a rethink on set up.

Requisitioned an old plastic rubbish bin much larger to allow both to be done at once, friendly word with BIL and hey presto, around a 3'x3' piece of new steel in my paws. Basic redesign was to cut steel so it went around the inside of the bin, with a steel disc welded onto bottom, this gives much more surface area I think to get the electrolysis to work better.

Simple to connect up and disconnect as needed, as before, the anodes kept moving and difficult to keep clean.

After two more days, with removing calipers every 8 hours or so to scrape off the crud, pulled them out, and clean as a proverbial whistle.

Both caliper bores have a slight surface blemish you can see, but cannot feel any ridges, only thing I can think is that the pistons were sticking and not coming out of the calipers straight. Pistons are basically scrap, as quite heavy pitting.

After pulling out of final dip, immediately went into the oven at 120 for 2 hours to try to prevent flash rust and remove hydrogen embrittlement problems hopefully. Almost perfect finish, and as Dave had suggested a polish of the bores with cotton drum pad with very fine metal polish, has cleaned them up a treat.

Just got to decide what finish now to put on the calipers, and rebuild with the Bigredd rebuild kit that includes new pistons. Any idea what factory finish was?? I would assume a grey type of plating similar to nickel plating?? Obviously will need to be high temperature paint.

Really pleased how they have turned out, only downside is the time it takes, keeping turning items around so anodes can 'see' all the surfaces.

Oh, make sure the better half is out whilst they're in the oven 😀😀

Cheers
Steve

[Laird Scooby]

I think (but may be wrong) the original finish was a yellow passivate over the basic caliper Steve. What you could do is copper plate it then nickel plate it but ensure you mask the bores as i believe they're chrome.

Quick method of cleaning the sacrificial anode(s) is to fit a piece of scrap steel in what would normally be the workpiece position (cathode) and then reverse the polarity so the sacrificial anodes become the workpiece and the "new" bit of scrap steel becomes the sacrificial anode.
This will clean and restore the real sacrificial anodes but make the "new" bit of scrap filthy which can be wire brushed off.

As for the "line of sight" principle, while that's mostly true, surrounding the workpiece with anodes as you've done or turning it occasionally helps get all the nooks and crannies. I keep thinking about using an old washer pump to move the fluid around but haven't got round to that yet.

If you want a bit more info on a quick and easy way to get the chemicals (i use that term very loosely!) to copper and nickel plate, just say.