Xantia rear brake callipers

[elma]

First job on the new car is the rear callipers.
The ones on the car are rusty and binding.
Luckily I found a decent, but dirty, pair of calipers in the workshop.

I'm nearly done cleaning them and I intend to paint them before fitting.
Question is:

The mounting face which tends to corrode,
is the best option
a:Paint it and fit them
b:Don't paint it, use a smear of copper grease to prevent the corrosion
c:Do both

My gut feeling is paint and grease, but I'm not sure or I'd just do it.

[Hell Razor5543]

The paint (if it is heat resistant) would be a good idea. The copper slip grease, less so. The corrosion that builds up is due to two dis-similar metals in very close contact, so introducing a third metal would complicate things.

[addo]

I'd disagree. For me, Wurth CU-800 on the mounting face of both arm and caliper. A tiny drop of Loctite in the threads of the trailing arm before offering up the caliper.

[citronut]

if you paint either or both you will alter the caliper to disc run out,

I'd disagree. For me, Wurth CU-800 on the mounting face of both arm and caliper. A tiny drop of Loctite in the threads of the trailing arm before offering up the caliper.

Adam i though at one time you ( or i think it were you??? ) advocated not to use a copper grease between caliper and arm but one containing aluminum

the like of one of

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

or am i having another senior moment yet again

[Xantidote]

I just clean up the faces by removing the rust (accepting that there's nothing you can do about the pitting of the calipers' face), and apply a copper grease. Having first done this 10 years ago, I have had to revisit and clean the faces again 5 years ago. Haven't checked recently if it's time to do it again. I wouldn't bother with painting the surfaces.

[CitroJim]

Martin, that's basically what I do and it serves me well..

Elma, one thing, be VERY careful about removing the old claipers. The bolts have a nasty habit of being very stubborn and they can shear..

With care they can be removed successfully but I'd always advise new bolts..

RichardW has done an excellent guide to removing stubborn caliper bolts on here. It'll be worth searching it out and reading his guidance...

I'd not be surprised if Richard himself doesn't soon pop up and give a link to his guide

[elma]

Thanks everyone.
Jim thats so true about the bolts, I broke one 6 years ago taking these callipers off.
They are a weird size, m7 or something if I remember correctly.
Already got bolts though.

Copper grease is the same thing as Titanium anti seize compound, used to stop galvanic corrosion between titanium and other metals.
It works well and will retard the corrosion by miles, I don't think it will amplify the effect.


I'll be painting the faces, not worried about runout as Citroen obviously weren't when they got the faces milled badly and not exactly flat in the first place.

Final note, if you swap the bleed valve to the other side and change the callipers from side to side the flat face that was facing outwards and is still quite flat can be used rather than the corroded totally not flat one that is usually against the mount.

All that remains to obtain is a pair of them tiny little pipe seals that go on the end of the brake lines.
Anyone know if I want 3.5mm or 4.5mm for the 1.9Td rear brakes?

[Hell Razor5543]

Is this any use?;

http://www.frenchcarforum.co.uk/forum/v ... =3&t=38467" onclick="window.open(this.href);return false;

[elma]

Is this any use?;

http://www.frenchcarforum.co.uk/forum/v ... =3&t=38467" onclick="window.open(this.href);return false;

Yes thanks, like the gasket idea, but still going with paint.

[CitroJim]

Is this any use?;

http://www.frenchcarforum.co.uk/forum/v ... =3&t=38467" onclick="window.open(this.href);return false;

That's a good 'un James. That was my old Rattiva II in those pictures...

[Hell Razor5543]

... and my first contribution to the forum.

[Mandrake]

Final note, if you swap the bleed valve to the other side and change the callipers from side to side the flat face that was facing outwards and is still quite flat can be used rather than the corroded totally not flat one that is usually against the mount.

I wouldn't count on that working - when RichardW and I tried to do this "swap the callipers" trick on my previous Xantia V6 we discovered that it wasn't possible - the inner bore on the bleed nipple side was not drilled to the correct diameter to insert the pipe. We had to swap the callipers back!!

We speculated at the time that replacement parts callipers have the correct diameter bore for the pipe on both sides so can be used either way around, (as there is only one part number for left and right hand sides) but the original factory fitted callipers are NOT bored to the same size on both sides of the calliper - probably to save money during production. Maybe they are identical on some Xantia's but definitely not on that one!

[RichardW]

Foxed us for a while that one Simon, didn't it

Info in a thread here http://www.frenchcarforum.co.uk/forum/v ... y&start=60" onclick="window.open(this.href);return false;, but Jim's is nicer with pics and all. Basically, remove the back plate, clean up the back of the bolts where they come through the arm and plus gas well. Get a decent 6 sided socket (may be 16 or 17mm - oddly estates with M10 bolts appear to be 16 rather than 17 which hatches with M9 bolts are.... ). Hammer then head of the bolt and the lug on the arm. Apply gradually increasing torque to the bolt with a decent breaker bar. Try hitting the back of the breaker bar head with the tension on. If it seems v tight, then heat the lug on the arm with a blow lamp - move the ABS wire out of the way - I wrap it in a plumbers soldering mat to avoid melting it. Try again with more gentle persuasion / more heat as required. Once it lets go, apply more Plus gas to the back, the go back and forwards a bit till it starts to ease up. Nip up the first one, before tackling the second one, to minimise the load on the first one.

[citronut]

Foxed us for a while that one Simon, didn't it

Info in a thread here http://www.frenchcarforum.co.uk/forum/v ... y&start=60" onclick="window.open(this.href);return false;, but Jim's is nicer with pics and all. Basically, remove the back plate, clean up the back of the bolts where they come through the arm and plus gas well. Get a decent 6 sided socket (may be 16 or 17mm - oddly estates with M10 bolts appear to be 16 rather than 17 which hatches with M9 bolts are.... ). Hammer then head of the bolt and the lug on the arm. Apply gradually increasing torque to the bolt with a decent breaker bar. Try hitting the back of the breaker bar head with the tension on. If it seems v tight, then heat the lug on the arm with a blow lamp - move the ABS wire out of the way - I wrap it in a plumbers soldering mat to avoid melting it. Try again with more gentle persuasion / more heat as required. Once it lets go, apply more Plus gas to the back, the go back and forwards a bit till it starts to ease up. Nip up the first one, before tackling the second one, to minimise the load on the first one.

although my findings are its not actually the thread through the arm lug that causes the bolt to hang on, but it is the copious application of stud N bearing lock/seal all the way the length of the bolt shank, through the caliper body

[Mandrake]

Foxed us for a while that one Simon, didn't it

Sure did. Especially after it being passed around as received wisdom on the forum for so long - I couldn't believe the pipe wouldn't go in, especially when looking at it visually it looks like it should fit, but the hole must be ever so slightly too small in diameter for the pipe to enter.

Both left and right callipers had the same problem too so it wasn't just one damaged or dud calliper.

I'm assuming that the diameter and finish of that inner hole is very critical to get a good high pressure seal (most of the sealing is actually metal to metal at the tip of the pipe not at the rubber seal) so during manufacture they probably drill out a rough slightly smaller hole first, then use another slightly bigger bit as a precision finisher - and not bother to finish the bleed valve side to save a few seconds during machining...

For replacement parts it makes sense to finish both holes properly to reduce the number of replacement parts skews held in stock...