Brake piston removal (after someone has bodged it)?

[armalites]

I've used air to free pistons loads of times, yes they can go with a bang but a piece of wood and a rag to cover and it will be fine, I'm generally more concerned about the fluid inside going everywhere.

Sorry guys but I am amused by people saying 120psi air will split pistons when a brake system is running 10 times that pressure, 120psi doesn't suddenly become 10000psi because it's in a brake caliper.

Not sure air is going to work if someone has been at it, I refurbed a set of 110 rear calipers recently that looked like they'd been washed up on a beach and air would not touch them and that is the first time I've ever had that happen.

I bought some grease nipple with the correct thread and used a grease gun, popped then out no problem but they went bang even with the grease.

When doing them with I find you soemtime have to work them in and out a few time, so give them some air, if they move but stop then pull the seal back and put some lube in and clean away any loose rust. Then push them back in a little and repeat, if they move then air will normally get them.

If using air then a blow tool with a rubber nozzle is very good as you can get a good seal.

All this get more tricky when you have more than one piston, sometimes you have to pop one piston clean it up and put it back and clamp it. If you use the a piece of wood of the right size you can get the pistons to the point where you can get a pair of grips on them.

 

[frank horton]

air prob won't shift it.......def grease gun route is the way to go...........after the heat what will the chrome be like...?..then there's the paint finish...........hardley worth the effort when ur life is at risk when back on the road.........
just get a rebuilt 1 if u can.......sorry
Frank

 

[Phil_D]

Grease gun every time

 

[arthur]

I've done ZILLIONS of caliper pistons of all sorts, use air, heat (only enough to soften rubber dust and oil seals), grease whatever, I also use, a brake caliper piston removal tool, they work great if the caliper is one in that you can gain access to it, stuck mono block bike calipers is another matter, I'd not recommend the vise grip style tool for alloy pistons or drilled and vented titanium nitride coated titanium pistons neither haha Oh and a loose rag can catch flying caliper pistons

 

[Alan Reynolds]

Do burnt seals contain a rather nasty substance that is quite harmful to your health if it touches your skin?

 

[8ob]

Do burnt seals contain a rather nasty substance that is quite harmful to your health if it touches your skin?

Apparently more toxic than a marriage, also applies to rubber that’s gone grungy.

Bob

 

[RonA]

I’m not sure why you would want to use air to free the stuck piston, apart from the danger of the thing flying off it all directions once free, the hydraulic system on the car/motorcycle exerts a far higher pressure using a fluid that is virtually incompressible & will only drip out once the piston finally comes free.
When I was working, our boilers were only ever hydrauliced to test them, wouldn’t ever dream of using air pressure, even if had sufficient pressure available.
RonA

 

[julianf]

what is the vehicle?

 

[mangocrazy]

I recently had to free up a pair of RD350LC calipers that had sat for best part of 25 years with old fluid in. Air wouldn't touch them. The only way I could get the pistons out of the calipers was by using a grease gun with an adapter made from braided hose with the correct size banjo to bolt to the calipers. That shifted the little bu99ers. Getting the grease out of the calipers afterwards was a game, but I couldn't have done it any other way. They were in a right state, but cleaned up to as new once they'd been vapour blasted and powder coated. The pistons were scrap, though. Had to get new ones.

 

[Justme]

Compressed air at 150psi is no where near the pressure in a hydraulic brake system, you'll never cause a caliper piston to split with air pressure. I've used a portapower pump to remove caliper pistons before and they will reach 10,000psi.

150 psi is hardly going to move a stuck piston if you cant get it out whilst its on the car using the brakes.

Plus the stored energy in 150psi of air is far greater than high pressure put not compressed fluid.

Thats why air cylinders are tested virtually full of water & very little compressed air.

Nothing to expand if it goes wrong.

 

[armalites]

I’m not sure why you would want to use air to free the stuck piston, apart from the danger of the thing flying off it all directions once free, the hydraulic system on the car/motorcycle exerts a far higher pressure using a fluid that is virtually incompressible & will only drip out once the piston finally comes free.
When I was working, our boilers were only ever hydrauliced to test them, wouldn’t ever dream of using air pressure, even if had sufficient pressure available.
RonA

If you are refurbing a calliper then you need to get the pistons out, if they not seized then a quick controlled blast of air get them out probably 95% of times. There is a big difference in pressure testing something and moving a sticky object. Dive cylinders are hydro tested but they are filled to 3000PSI and we are talking about 100-120 PSI in a tiny little space it's not an atom bomb! Sure you need to use common sense, blocks of wood and cover them up.

A fizzy drinks bottle will take 120PSI.

 

[zx9]

Lots of fun in one of them, fond memories.

 

[julianf]

Right - if im to re-assemble it, (its in two halves at present) ill also need to resolve the fact that the bleed nipple has been snapped off, and half of it remains screwed in.

Wonder if a stud extractor would work - ive never (as in not even once) had any luck with stud extractors in the past!

 

[zx9]

Right - if im to re-assemble it, (its in two halves at present) ill also need to resolve the fact that the bleed nipple has been snapped off, and half of it remains screwed in.

Wonder if a stud extractor would work - ive never (as in not even once) had any luck with stud extractors in the past!

I know they are only small, is it broken too far down to weld a nut to?

 

[steviec_lj]

Right - if im to re-assemble it, (its in two halves at present) ill also need to resolve the fact that the bleed nipple has been snapped off, and half of it remains screwed in.

Wonder if a stud extractor would work - ive never (as in not even once) had any luck with stud extractors in the past!

Can you weld a nut to the top of what's left? Only had to do it once previously myself..

Edit.. Beaten to it by zx9

 

[The_Yellow_Ardvark]

Wonder if a stud extractor would work - ive never (as in not even once) had any luck with stud extractors in the past!

Left hand drill bit.

 

[armalites]

Right - if im to re-assemble it, (its in two halves at present) ill also need to resolve the fact that the bleed nipple has been snapped off, and half of it remains screwed in.

Wonder if a stud extractor would work - ive never (as in not even once) had any luck with stud extractors in the past!

I guess there is much swearing to come yet

 

[The_Yellow_Ardvark]

I guess there is much swearing to come yet

You are far away and may not hear it.
I am near by and I can.

 

[DaveB]

Do burnt seals contain a rather nasty substance that is quite harmful to your health if it touches your skin?

Many seals are no longer rubber in the pure sense but a modern synthetic elastomer.
Some of these can decompose when heated and form hydrofluoric acid.
The easiest treatment for human flesh exposed to hydrofluoric acid is removal, with prejudice !

Forgot about the grease gun trick.

If the caliper is split and you can get a new piston then a lathe is probably your friend.

 

[mangocrazy]

Unless I'm mistaken, the caliper on that bike doesn't split. It's not like modern Brembos, two machined halves joined by allen bolts; it's a crappy floating caliper design with just the one piston. In which case, a grease gun is your only real friend. Once it's out you can use a lathe to knock up a replacement stainless piston, but that's about it.