Caliper sticking?

[Deluks]

Been having some metallic scrapey noises from my Polo (mk3 '94) recently. Noticable when driving at slower speeds even when the brakes weren't applied.
So I had a look at the front calipers yesterday, undid them, removed pads (plenty still on 'em) sprayed the lot with brake cleaner and re-asssembled. Seems to have solved the noise problem for now, but I noticed on assemble that the nsf wheel does not turn freely, and I suspect the the piston or other caliper part may be sticking, which may have caused the pads to contact the disc whilst driving.

So I'm considering refurbing the front brakes.

Not au fait with the workings of brakes and calipers, I've read elsewhere about sliders. Would my calipers have these? and am I right in thinking that they are what the 2 allen head bolts round the back, screw into?
I was under the impression that the back of the caliper body is securely fixed in place and doesn't move. ?

So if I were to take apart, clean and refurb the calipers, what tools/lube do I need? Copperslip is on the shopping list already as there was hardly any on the backs of the pads. What sort of grease would I need for the other bits?

 

[Burnerman]

The caliper is held onto its bracket with two allen bolts, accessible from the back. These are in fact sliders, which allow the caliper to exert equal pressure on both sides of the disc.
The sliders must allow the caliper to move - if it doesn't then the brakes will certainly bind on one side.
Do use the correct size allen key - I think its 6mm but usually there's plenty of grot in the heads to try a 7mm first.
Use coppaslip to lube the backs of the pads and any metal to metal sliding contact. If metal comes into contact with rubber then red rubber grease is best (made by Granville).
Do one side at a time, and notice the pads aren't the same shape on these.
If the rubber dust seal is split over the caliper piston, expect some rust to be in there, but if the piston pushes back ok then alls well.
Careful you don't lose those thin stainless anti rattle shims!
Enjoy!
John

 

[gblades]

Check the pad wear on the inside and outside of the disk and it should be even. If the pads are more worn on the side with the piston then the sliders might be sticking.

A lot of the time it's the piston getting corroded and causing it to stick when it gets pushed back in further typically after fitting new pads. You can try cleaning them but sometimes you just need new calipers.

Go for a drive and after stopping feel the hat coming off the discs. If one side is a lot hotter then that's a good indication it is sticking.

 

[Deluks]

Ok guys, thanks for the good advice.

Just cracked the wheels off again, have left calipers attached to flexi hoses for now (supported)
The sliding action of the caliper is non existent!
The two sleeves through the bolt holes were seized and unlubed, I actually had to refit the cals minus pads, and try and free them up by pushing and tapping them hard to confirm that they could move.
Managed to get the metal sleeves out with an 8mm long reach socket and a hard tap. Now to clean them up and replace, but with what should I lube them with? (Even temporarily as I need the car for tomorrow?)

Picked up some copperslip for the pads.

Haven't had a go at trying to move the pistons yet (do the hoses need disconnecting to make this happen by hand?)

Will try in a mo with a g-clamp, and some grips to see if they'll turn slightly.

If I end up having to remove and clean up the pistons too, what should they be lubed with, ideally?

 

[gblades]

Regular grease should be fine or you could use lithium grease which tends to be more water resistant.

To move the pistons just loosen the cap to the brake fluid reservoir. You will need to push the pistons back but never try twisting them. They will probably have piston rings to keep themselves sealed from the brake fluid which will act as a lubricant aswell.
If they are badly pitted with corrosion then they will need to be taken out, the caliper holes for the pistons remachined to make them smooth again and the pistons refitted with larger piston rings. Thats why if its a garage doing it just buying new calipers is cheaper than the labour and delays is getting them reconditioned.

 

[Stivino]

If you get a caliper repair kit, it should come with the proper grease for the slides.
http://seekpart24.com/bosch/repair-kit-brake-caliper-1987470040

 

[Burnerman]

If you want to try refurbishing the caliper, it really needs to be on the bench and completely clean - which naturally enough involves splitting the brake lines further up.
The pistons can be pushed out using compressed air (gently) or by the foot brake, before they are disconnected.
When lubricating any parts that contact rubber, use a proprietary rubber grease (red stuff) - normal mineral stuff will slowly rot the rubber away.
However, if the pistons push back in readily enough - and then come back out again with a couple of pedal pumps - don't worry about them.
Personally, if the caliper needed attention, I'd pop an exchange one on.
John