Front calipers sticking

[Derskine 11]

Just finally finished overhauling my brakes, the rear brakes are perfect, oh how I wish my car had the drums on the front :thumbdown:

Anyway, my car has m16 calipers fitted to the front, they work fine except that when the pedal isnt applied they still grip the disc.

Do I need to centralise them? How do I do this?

Thanks,

[richard 2509 0]

Just finally finished overhauling my brakes, the rear brakes are perfect, oh how I wish my car had the drums on the front :thumbdown:

Anyway, my car has m16 calipers fitted to the front, they work fine except that when the pedal isnt applied they still grip the disc.

Do I need to centralise them? How do I do this?

Thanks,

dont do what i did many many years ago when i sprayed the discs with wd40 to stop the brakes binding!!!result no front brakes at all. :rolleyes:

[consul315 180]

Just finally finished overhauling my brakes, the rear brakes are perfect, oh how I wish my car had the drums on the front :thumbdown:

Anyway, my car has m16 calipers fitted to the front, they work fine except that when the pedal isnt applied they still grip the disc.

Do I need to centralise them? How do I do this?

Thanks,

 

have you changed the hoses as well, if not try to open the bleeding valve and see if pressure "escapes"? did the pistons slide in gently when you reassembled them and can you move them? :cheers:

Edited June 24, 2011 by consul315

[Derskine 11]

I replaced the hoses yes hans, I did clamp them with mole grips though so maybe they've broken?

The calipers were from a capri and I believe they were serviced quite recently.

The pistons grip even tighter when the brake pedal is pushed so I dont think thats a problem.

I haven't replaced the master cylinder and its been on there for probably all the cars life although it does seem okay.

And to richard, they're really jammed on, not just a tiny bit, but advise taken, don't lube up the brakes! :rofl:

Edited June 25, 2011 by Steelrax

[Derskine 11]

I think maybe get the calipers off, get the dust covers off, spray some wd40 or put some copper grease (?) on the pistons, I think the problem is they're maybe a little sticky without any lubrication and the pressure just isnt enough to suck them back in.

I forgot to mention my car has the standard 5/8 master cylinder, would I need the bigger 0.7" or 0.75" ones bearing in mind I have m16 calipers, could be being thick again but since the calipers have a bigger bore surely the master cylinder should have a bigger bore?

Edited June 25, 2011 by Steelrax

[consul315 180]

I think maybe get the calipers off, get the dust covers off, spray some wd40 or put some copper grease (?)

 

 

don t take copper grease, it will dry out soon and harden, i always use a special brake grease (in my case "ATE blue").

sorry can t give advise on what size of m-cyl. with different calipers!

[Derskine 11]

I think really all it could be is the master cylinder not giving enough back pressure or the pistons being a little sticky.

Edited June 25, 2011 by Steelrax

[Derskine 11]

What bore is the master cylinder on lotus's?

I'm sure that's something to go on since m16s/p16s are near identical?

But I'm still going to dismantle the calipers and have a look see - probably replace the seals

[fatboy 0]

.75 on a lotus.

[G.O 20]

Bore size of master cylinder is only important when you push the pedal (governs ratio of pedal to brake piston movement) but it makes no difference whatsoever when not pushed, none should keep the pressure on the brakes. You say the rears are fine? In which case it's safe to assume the problem isn't with the master. Could be the hoses have collapsed but also make sure the calliper pistons haven't seized. Try fitting an old set of worn pads, and then use them to work the calliper pistons in and out again and again to make sure they are free.

[Derskine 11]

Bore size of master cylinder is only important when you push the pedal (governs ratio of pedal to brake piston movement) but it makes no difference whatsoever when not pushed, none should keep the pressure on the brakes. You say the rears are fine? In which case it's safe to assume the problem isn't with the master. Could be the hoses have collapsed but also make sure the calliper pistons haven't seized. Try fitting an old set of worn pads, and then use them to work the calliper pistons in and out again and again to make sure they are free.

 

I've been swaying more to the seals in the calipers being naff, the pistons do come out, just don't go back in fully, I've bought a kit so I'm going to replace them all and lube the pistons a little, any advise on removing the pistons without air pressure (eg using the brake pedal) without spraying fluid everywhere?

But thanks for the advice, didn't really fancy shelling out on a new master cylinder!

Cheers

Edited June 26, 2011 by Steelrax

[MK5CortinaEstate 54]

My bet is on sticky pistons, especially as you say they won't go all the way in.

 

When you come to disassemble them, use a couple of levers in the groove the dust seal sits in. You may need to push the piston back in several times before it is free enough to come out. Twisting the piston slightly to free it up as it comes out is an option as well. Slight damage to the outer diameter of the piston outside the dust shield is OK, but if you damage the the outside diamter of the piston behind the dust shield, the piston will be effectively scrap.

 

Once apart, dig out the old seal and discard, and clean thoroughly. Wire wool works well on the outside of the piston, without damaging in. Any pitting or scoring on the outside of the piston, and it's scrap again.

 

When you come to reassemble, lube the seal and piston with brake fluid. Remember, the seals are designed to work with brake fluid, and therefore oil (including WD40) will damage them.

 

Good luck!

[bortaf 94]

I'd go for rusty pistons grabbing the seals or somone has used some silicone lube spray at some time that has swollen the seals and that makes them grab the piston as well, personly i'd rebuild them using only brake fluid or as hans says brake grease that's rubber safe ;)

The master doesn't suck the pistons back the return spring in the master isn't stronge enough for that it the play in the bearing (disc runout) that knocks the pads back and or the build up of gasses from the heat produced by the pad running on the disc that seperate the 2 surfaces pushing the piston back in (IF that is the hydrolic pressure has dropped enough to allow it to happen) ?

[Derskine 11]

I'd go for rusty pistons grabbing the seals or somone has used some silicone lube spray at some time that has swollen the seals and that makes them grab the piston as well, personly i'd rebuild them using only brake fluid or as hans says brake grease that's rubber safe ;)

The master doesn't suck the pistons back the return spring in the master isn't stronge enough for that it the play in the bearing (disc runout) that knocks the pads back and or the build up of gasses from the heat produced by the pad running on the disc that seperate the 2 surfaces pushing the piston back in (IF that is the hydrolic pressure has dropped enough to allow it to happen) ?

 

I've taken a caliper off and used a bike bump/tyre valve in the brake fluid inlet to remove ONE of the pistons, the other was pretty darn seized, I put the other piston back in, clamped, pumped up to a SAFE pressure and it didnt come out, stuck it back on the car and slammed the brake pedal, it popped out nearly all the way, I think theres probably a lot of pressure building up inside the calipers causing the other piston to not return.

I think on the other side the pistons are both seized.

No pitting/rust at all on the pistons though, just a case of fitting new seals + lubing I think :thumbup:

[Derskine 11]

New seals came today, so went crazy at the calipers with the bike pump/tyre valve to hear that frightening BANG, although, very happy that it finally came out :icecream:

The very top of the cylinders, not the pistons, were a little pitted, so a light sand and good as new, fitted new seals, lubed up with brake fluid and they went back in a treat, mind you, ruined the paint on them with brake fluid everywhere!

Not to worry though, its a nice day so I'm quite happy to repaint them.

The other one is still on the car and I dread to think how hard these pistons will be to get out, but perseverance...