Caliper refurb, request for advice

[stevie_b]

I'm currently removing my front J-spec calipers for a refurb. I'm a bit stuck though and I'm looking for quick advice. I've split the calipers in two, and currently trying to push the pistons out whilst the hydraulic lines are still connected. On both sides, one of the pistons is stuck in the "in" position or thereabouts, whilst the other piston is very much "out" (and both the out ones' seals are weeping brake fluid).

 

I've tried pushing the "out" ones back in with a g-clamp, but they're not budging. Shall I just remove the brake line and try to extract the stuck pistons once the calipers are off the car? Id so how do I do that?

 

I need to put the car away in an hour max before the sunlight goes, hence the urgency.

Edited December 23, 2012 by stevie_b (see edit history)

[Porky1978]

Have you undone the reservoir cap to allow the fluid to drain back?

[stevie_b]

Yes, I'd undone the reservoir cap. I've now taken the calipers off, so hopefully I'll be able to get those pistons out!

 

I read about some pliers here, so they might come in useful.

http://www.mkivsupra.net/vbb/showthread.php?26573-Brake-caliper-disassembly

[stevie_b]

I've only a fraction of a litre (guess 100ml) from the brake lines as I took both front calipers off. Is this normal? I thought the brake system had a 1.5 litre capacity, and the reservoir was fairly full before I started. There's still a bit of fluid in the reservoir, but I don't understand what's holding it in the system.

 

Any ideas?

[Scooter]

On the fronts one piston is in line with where the brake line fits, if (sods law says it isn't) it's this piston that is currently stuck then you can put something thin but strong, bolt/nail etc down the hole onto the back of the piston and then using a vice/g-clamp/car jack etc to force that bolt in to the restrained caliper section and hence force the piston out.

 

Also check this out if you haven't already seen it.........

 

http://www.mkivsupra.net/vbb/showthread.php?64963-Urgent-Caliper-Help&highlight=caliper

[stevie_b]

Thanks Scooter. One of the calipers has the stuck piston that's in line with the brake line fitting, but the other caliper isn't. I'll give it a go one that one.

[Dnk]

If you can't get the pistons out using the cars hydraulic system and you have

a piston that's properly seized.

 

Carefully hold the caliper in a vice and using caliper pliers or even pipe grips with

some 120 grit emery cloth wrapped round the top end of the piston and try to rotate

the piston back and fourth.

 

If they won't move doing this remove the outer seal, sit the caliper flat on a bench

with the pistons facing up and soak them in penetrating fluid around the piston and

leave for a few hours then re try the above, on the single piston rear you can try compressed

air but on the fronts you need both pistons in the caliper and hold the free one in place with

a g clamp.

 

Edited

 

As Chris says be careful using the compressed air route.

 

I used this on the 4 piston UK type calipers and had a piece

of wood in between the pistons so none of them could come

out completely.

Keep your fingers out the way

Edited December 25, 2012 by Dnk (see edit history)

[Chris Wilson]

BE VERY CAREFUL using compressed air, when a piston comes out with compressed air it's like a missile, or can break fingers. Because the air is compressed.... Fluid doesn't compress and is much safer. You should have wedged the moving pistons to stop them coming out so far as to pass the seal. Hindsight ehh?

[stevie_b]

An update: thanks to Scooter's advice in this thread (also mentioned by Digsy in an old thread) I managed to extract one of the stuck pistons.

 

The other piston (the one that's not in line with the hydraulic feed hole) is still stuck. I have three choices:

1) buy some caliper piston pliers, and hope I can get enough grip/force on them to budge the piston. e.g. http://www.diytools.co.uk/sealey-vs1806-motorcycle-brake-piston-removal-pliers.html

Disadvantage: might not get enough force on it.

2) buy a push-back tool to try to get the free piston back in its cylinder. Disadvantage: might not be able to push it in.

3) Refurb the free piston including replacing the rubber seal, refit the piston, connect it up to the car hydraulics, bleed, chock the free piston with wood blocks to force the stuck piston out. Disadv: might need to refurb the free piston twice (new seals) if I contaminate it with crud/rust when I finally extract the stuck one.

 

I'm pretty sure both pistons on this caliper were moving OK 4 or 5 months ago, so I don't think the stuck one is seized for good.

 

Any suggestions?

[Dnk]

Why don't you try what i suggested and use some small

pipe grips and see if the piston will rotate.

 

I've used this method on the 4 piston calipers and if you wrap

some emery cloth round the top end of the piston it wont harm

them as your not on the outer diameter where the inner seal works.

 

Failing that.

 

The piston that's come out should push back into its cylinder with

just the pressure you can apply with your hands.

 

Just pop the inner seal out and get the piston, piston bore and seal clean,

pop the seal back in its groove then just push the piston back into the

piston bore.

You can use a smear of brake fluid to make this easier

Edited January 1, 2013 by Dnk (see edit history)

[stevie_b]

Thanks Dnk,

 

I tried to wiggle the piston out with a variety of tools: rubber strap wrench, nylon strap wrench (oil filter removal tool, basically), mole grips, plumber's adjustable spanner (pipe grips). The strap wrenches just slipped on the piston. The mole grips and plumber's spanner started to score the surface of the piston, despite using some 120 grit sandpaper as a protective barrier. It's only scored the tapered tip of the piston, as that's the only part that's peeking out from the caliper, but I didn't want to continue and knacker the surface.

 

Having read your post though I guess the tapered tip doesn't matter too much. It's the cylindrical body that needs to be kept free from scratches. How much did you scratch your piston tips by using pipe grips?

[Chris Wilson]

You may have top sacrifice the piston to get it out unless you pop the other one back and hydraulic it out. You are not being anything like brutal enough to get a tight one out. If it's REALLY tight the only way is hydraulics. You might lever it out with two big pry bars under the lip for the dust bot, or at least get it moving. Spraying with penetrating oil and using heat may help, but if you get it hot enough to do much good the piston seal will be fried, so you no longer have the option to hydraulic it out. Who ever said refurbing calipers was easy. Not me!!!

Edited January 2, 2013 by Chris Wilson (see edit history)

[Dnk]

The ones i have done rotated and then eased out without damaging the pistons.

 

If yours wont budge then i'd be inclined to pop the other piston back in and

bolt it back onto the car, bleed the caliper up but retain the free piston so it

can't come out and hopefully the stuck one will pop out.

[stevie_b]

I think I'll try to get it out using the car's hydraulics or compressed air.

 

Dnk, you mentioned I should clean the piston and its bore before putting it back in. The free piston hasn't actually fully popped out, it's just loose at the limit of its travel. The dust boot is still in place and hasn't perished or popped off as far as I can see. I presume that means the cleaning is unnecessary as no dirt should have entered the caliper.

 

You also said I should pop the inner seal out. I guess this also isn't necessary if the free-moving piston hasn't left its bore?

[Chris Wilson]

DO NOT use compressed air. You'll need a thousand PSI or more if it's stuck, and 1000 PSI + of air behind the piston, once it moves, is like a grenade. You'll hurt yourself, damage something nearby, or have the Old Bill round. Oh, you ARE the Old Bill, scrub that

[Dnk]

I think I'll try to get it out using the car's hydraulics or compressed air.

 

Dnk, you mentioned I should clean the piston and its bore before putting it back in. The free piston hasn't actually fully popped out, it's just loose at the limit of its travel. The dust boot is still in place and hasn't perished or popped off as far as I can see. I presume that means the cleaning is unnecessary as no dirt should have entered the caliper.

 

You also said I should pop the inner seal out. I guess this also isn't necessary if the free-moving piston hasn't left its bore?

 

If the free piston hasn't come out the inner seal then just push it back in and then

stop it from coming out.

 

If its bolted back on the car you can use a piece of wood to wedge

between the disc and free piston to keep it from coming out

before the one that's stuck.

 

I've used the compressed air route but had the caliper in a vice with wood

between the pistons only allowing them to move say 5 mm and not just

firing out into space and bringing down passing aircraft

 

This was only because i didn't have a car to bolt them onto or i would

have used the cars braking system as this is safer and easier.

Edited January 2, 2013 by Dnk (see edit history)

[stevie_b]

Understood, thank you guys.

[stevie_b]

I have another question, about greasing the moving parts. I'm confused about the need for grease.

 

Is (red rubber) grease necessary? Surely the dust boots on the pistons will keep the piston walls clean, and the brake fluid will lubricate them too. I can't see why grease on the pistons is necessary. I've heard that some people use grease to lubricate the surface between the piston head and the metal plate that the pistons push against (the one that backs onto the brake pads). I know those two surfaces shouldn't really be moving relative to each other, but I can see that the braking forces might cause them to shift a little bit, and some grease would help them settle into their relative positions when the pistons retract into their bores.

 

Can I use red rubber grease on the slider pins? They're the parts where I can see I *do* need to apply grease, because they have a tendency to stop sliding after a few years.

[Chris Wilson]

Red rubber grease is to help the pistons slide into the new seals, and should NOYT be used on the sliders, you need a high temp moly grease on those, I use Neo racing CV joint grease, designed for CV joints inside inboard rear discs, where the joint gets stinking hot. Ideal for brake sliders, but it's expensive unless you need it for its proper purpose, too. Back of pad to pistons use copper grease, or nothing. With anti squeal shims fitted you don't need anything there. I would use red rubber greae on the pistons myself, but you can just lubricate the seals and pistons with clean new brake fluid, the key word is clean. Everything inside the caliper must be spotless.