caliper slide play

[Wookey]

Hi chaps. I have an expert van with (front) bendix calipers. It doesn't get used much and I've had trouble with rusting discs for the last couple of years, but this year the rotors are in a reaosnable state. However, on a run to Yorkshire I noticed a warm wheel (when putting air in) and there is an annoying squeak, stopped by braking. The wheels were very stiff to rotate when I jacked it up, and it has duly failed its MOT on 'binding front brakes' (both sides), which seems fair enough under the circs. I've just lifted up the calipers and on both side the slide move very freely and so do the pads in their slots.

There is a bit of play in the slide - is that OK, or should there be none? Could play here be responsible for binding as it lets the caliper rotate a tiny bit out of parallel (from the rotor)?

What else might be causing binding? The piston not free in the caliper I presume? The MOT fellow suggested that occaisionally you get collapse inside the brake hose making a sort of heart-valve so the fuild can't return? I've bought a couple of new hoses as they are 16 yrs old and not expensive (getting the old ones out is going to be fun, I bet). One thing I've never understood about disc brakes - what is it that pushes them back off the rotor surface? There doesn't actually seem to be anything that does that? Is there somethig in the hydraulics which 'sucks' a little to pull them back a touch?

Any other things to look for?

Sadly I'm in a hurry as I'm driving to Austria in 10 days for hols and not having an MOT will be a pain. (having the MOT up against summer hols is not a good state, although at least the weather is good What I need to know is whether I need to change the calipers, or what other tests I should do to get to the root cause so I can order things in time. I guess calipers are expensive, and I understand that's rarely actually needed?

One other detail - the pad shims have basically rusted away almost completely. I tried to buy new ones last year but peugeot didn't have them. Are these in fact pointless and I should just forget them.

[Wookey]

A bit more investigation: pushing the pot in then, with the caliper in free space having someone push the pedal, it comes out, then relaxes back approx 1-2mm, over the full usage range. So that seems a lot like 'working properly'. Letting the brakes work on the rotor, after taking foot off pedal there is some rotational drag, but not excessive, which I think is fairly normal? (is there a test for 'reasonable brake drag'?) So it seems to be working OK, and I've not found anything obviously wrong, which is kind of unsatisfying. NOw I'm nto sure whether to just take it back for retest or start taking things to bits further (new hoses, new pipes, disassemble caliper and clean/service?

[Peter.N.]

If the piston is sticking try pulling the rubber seal on the piston back and squirting some brake fluid in, it should work loose after a few applications. If the vehicle is not used much the damp can get in and rust the piston/cylinder.

Peter

[citronut]

If the piston is sticking try pulling the rubber seal on the piston back and squirting some brake fluid in, it should work loose after a few applications.

Peter

the only prob i can see with this is the MOT tester might suggest you have a fluid leak at your caliper,

maybe Wookey could just remove the pads clean everything up, copper slip the moving parts and backs of pads, then re/fit and re/present to the MOT station

[Peter.N.]

Yes that could be a problem, although if it can't be wiped off, unless its just prior to the MOT I think brake fluid dries up fairly quickly. I used to do this with my hydropnumatic Citroens but they used hydraulic fluid in the braking system which didn't dry up so quickly. I have found this very good for releasing partially seized pistons, once you get it in if you can work them backwards and forwards by means of a tyre lever and the brake pedal they usually free off quite nicely.

Peter

[Wookey]

So I fiddled a bit more and the pots slide in with hard hand/thumb pressure, and don't obviously bind, until I put the caliper pin back in. Then if I pushed the brake pedal hard the pads (on the side with the pin in) didn't release, and the wheel was very hard to turn. So I've reproduced the problem, but am not sure what to make of it. The caliper is held a few mm closer to the hub with the pin in, but why would that make it bind? Does it need to move along that pin as it does the slide at the other end? I guess there could be plenty of friction there. I'll try greasing it up.

I have some silicone service grease (servisol). Anyone know if that's high-temp and thus OK for brake slides or is there special high-temp silicone grease for this application?

[citronut]

So I fiddled a bit more and the pots slide in with hard hand/thumb pressure, and don't obviously bind, until I put the caliper pin back in. Then if I pushed the brake pedal hard the pads (on the side with the pin in) didn't release, and the wheel was very hard to turn. So I've reproduced the problem, but am not sure what to make of it. The caliper is held a few mm closer to the hub with the pin in, but why would that make it bind? Does it need to move along that pin as it does the slide at the other end? I guess there could be plenty of friction there. I'll try greasing it up.

I have some silicone service grease (servisol). Anyone know if that's high-temp and thus OK for brake slides or is there special high-temp silicone grease for this application?

firstly can you send me the last 8 digits of your chassis/VIN No. so i can look at exactly what type of brakes your Stealth has,

secondly here is a link for copperslip ( brake grease/lube

https://www.google.co.uk/#q=copper+slip&tbm=shop" onclick="window.open(this.href);return false;

[Wookey]

VF3**************[VIN obfuscated, can be read by forum staff]
Going from the rotor dimensions in my Russek book they appear to be the Bendix brakes.
like this: http://www.ebay.co.uk/itm/PEUGEOT-EXPER ... 3a9209e767" onclick="window.open(this.href);return false;

There is a little metal U-shaped shim in the slot at the end of the caliper through which the pin goes which holds it in place. That's in good condition, but the pin is quite tight fit into it, which may explain why the caliper stops being free to slide properly when it's in? It seems odd that the slide pin has a rubber boot and beautifully machined surface, whilst this pin is just a chromed pin, exposed to the air and not normally liubricated (or maybe I should have ben all this time....). Given that the caliper has to be able to slide on both of these things. I can remove the shim and put the pin back and everything slides rather better. Oddly there doesn't seem to be much corrosion behind the shim pushing it out.

Just been for a drive and everything works nicely. No rattling, even braking and no binding when back, so I think I'll send it back for a retest like this and get the MOT man off my back, then do a more thorough caliper refurb at my leisure.

[Wookey]

OK, going back with the shim missing has got me an MOT, so now I can deal with this at my leisure, which is a much more comfortable state of affairs. I'll give it all a good clean/derust and lube at the w/e and then probably drive to Austria and back and see how it goes.

[Wookey]

OK, so another year has dashed by and I get round to fettling the brakes again.

The van worked fine after some greasing-up. No binding or pulling. However after a year the nearside rotors are fine, but the offside inner surface is somewhat rusty (not badly, with scaling, but not clean steel like it should be, so pad pressure is obvisouly low, and the outer pad is worn ~1.5mm more than the inner one. (the van went to Devon at new year, Poole in feb, sat for a few months and went to Derbyshire last weekend so has been recently used.).

So it seems that one caliper still isn't working right.

One thing I don't understand: Why would the inner (simpler) side work worse? i.e. as the piston is on the inner side, why would the pad on that side apparently be not moving enough, whilst the other side (which needs the slider to move as well as pressure from the piston) be moving more/applying more force? Surely if the piston is pressing then the pad it is working directly on should move - the only thing that could impede it is the 'cups' where the ears on the pads sit - right? And I filed the rust off those and copperslipped them last year (4000 miles) ago.

Is it perhaps that if there is a bit of slop on the slider bolt, because the piston is on the moving part it stays aligned with the outer-side pad, but is slightly angled to the inner pad and that causes the differential pressure.

Anyone understand why this happens?

[BX]

On a van that's getting used like that I wouldn't worry too much about the outer pad wearing a little more than the inner as long as the brakes pull evenly and release when they should. If you are going to do any work on them you could do worse than get kits to overhaul the callipers. You need 2 kits for each side. One kit contains the slides the other has the piston seal and dust cover. Pump out the pistons completely and then remove the calliper. There is a small area between the dust cover and the hydraulic seal that often rusts. Sand this down to clean metal then polish off the surface with 400 then 800 grit wet & dry paper which you keep lubricated with brake fluid. Clean and polish the pistons with steel wool, wet & dry and brake fluid. When this is done rinse off all with brake fluid and dry all the surfaces. Lubricate the piston and the cylinder surface outside the hydraulic seal with either special brake grease or synthetic hydraulic grease.Replace the seal, the dust cover and the piston. Likewise clean out the slides and rinse them with petrol. Fit the new plastic dampers to the new pins. Lubricate all with the grease supplied and fit the new pins along with the new bellows seals. If a brake has got very hot the plastic dampers on the slides can start to melt and cause intermittent binding. When dismantling make a note of the 2 pins as they are often different. Frenkit is a common brand name if you are looking up kits. The same kit will usually fit several different vehicles with that particular braking system so go more on the details of the brakes rather than the vehicle make or model.
These links are just to show what you are looking for
http://www.ebay.ie/sch/i.html?_odkw=fre ... t&_sacat=0

http://www.ebay.ie/itm/Guide-Sleeve-Kit ... 4188de8e84

It is also possible to get brake discs which are not prone to rust. These can be expensive.

[Wookey]

Where can one find 'rust-resistant' discs for vehicles that are sat around a lot? I failed to find such a thing when I had a look?

Thinks for the info on the refurb. It does indeed lok cost-effective, but I do have to remember to do it in a gap when I'm not using the van. In theory that's easy, but in practice it always ends up just before I want to go somewhere

I take it that changing the sliders with one of those kits will remove the slop on the slider pin (I.e it's a replaceable bit that wears, not the metal body)? I do have a bit of slop you can feel and worry that my slider is just worn, so replacing all the gasket bits won't actualy help.

[BX]

There is usually a little play/slop but one of the pins usually has a plastic sleeve / rattle damper. When wear occurs it is not usually even aling the length of the pin and can cause the caliper to rattle or to sometimes stick.
Coated and corrosion resistant discs are available from pagid and brembo and maybe from some others. A garage here used to get them from a supplier in Northern Ireland. He used them a lot especially on farmers vans where mileage might be low but conditions poor. I never used them myself. I would need to ring him to find out more.

[Wookey]

So I took the caliper off, and got the old slider boots off. The slider is very rusty at the ends so obviously needs replacing. The boots have become disconnected from the metal mount so also clearly need replacing. http://wookware.org/pics/van/calipersli ... 9.JPG.html

However, the bushes are trickier.

How do you get them out? With a press? Can they be driven all the way through?
The existing ones are not in bad condition - not rusty - it just looks like a bit of the teflon(?) coating on the inside near the edge has been lost. Just putting in the new slider, bolt and boots on looks like a _lot_ less work than trying to replace those bushes too.
Pic shows state:
http://wookware.org/pics/van/calipersli ... 8.JPG.html
http://wookware.org/pics/van/calipersli ... 7.JPG.html