Citroen Xantia Brake Pads

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AceTinker
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Citroen Xantia Brake Pads

Post by AceTinker »

Can someone please tell me why my Citroen Xantia Front Brake Pads have a pin protruding from the metal side. According to Haynes, it is a Locating Pin which engages with the slots in the face of the piston in the brake cylinder - but why??

Every time I have had to remove the inner brake pads, this pin snags with the piston face making it really difficult to remove the brake pad. This time I got so frustrated with it, that when I did eventually remove the pads, I decided to grind the "locating pin" from both inner pads.

They are now easy to remove and replace, but I am now worried in case this has some detrimental effect on my brakes. They seem to be working fine so far, but I would still appreciate your views.
addo
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Post by addo »

The reason they're there, is sort of curly.

Your handbrake acts on the front calipers. In operating the handbrake, the lever on the outside of the caliper, rotates a shaft that runs up the guts of the caliper's piston bore. This shaft has helical "threads" cut into it, that engage with a boss circlipped into the back of the caliper piston.

The boss is able to rotate independently of the piston, although it deliberately has considerable friction.

Action of the handbrake makes use of the helical threads to push the piston outwards. The grooves in the piston index to the pad pin you note, so the piston doesn't rotate in and out merrily but takes up slack in the mechanism as your pads wear.

The likely outcome of your grinding, is very little actual effect. Worst case, you lose the ability of the caliper to take up pad wear.
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Re: Citroën Xantia Brake Pads

Post by Xaccers »

Not sure that is correct Addo.
When the brakes are used the piston winds down the helical shaft. When the pads are applied, the piston cannot go any further so stops rotating. The helical shaft is also on a return spring so when you release the pressure it pulls the piston off the pads slightly.
If memory serves the pip on the back of the pads actually sits inside the circumference of the piston face.
It may be that this position helps hold the pad in alignment, but I think the pip is just there because they hate us.
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Re: Citroën Xantia Brake Pads

Post by addo »

Here's the detailed "explanation".

Image

Trust me, the pin does locate in the piston slot. Mark one on a caliper you have just fitted or rebuilt, and see how it stays put. What the picture shows, is how the centre of the piston can rotate independently of the piston "shell".
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Re: Citroën Xantia Brake Pads

Post by Citroenmad »

It does seem a bit of an odd idea and certainly does not make removing or refitting pads easy. C5s do not have this feature but yet have very similar front brakes, of course with the handbrake on the front too.
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Re: Citroën Xantia Brake Pads

Post by Xaccers »

If it sat in the piston slot, the piston wouldn't be able to rotate beyond that slot and so it could never be unaligned with the slot and the calliper half would never catch on the pip when you lifted it up to change pads though.
I know that isn't the case as one of Jenny's callipers was caught on the pip the same as AceTinker
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Re: Citroën Xantia Brake Pads

Post by AceTinker »

Thank you all so much for your responses - I really didn't expect this much detail. The piston heads on mine seem to be castellated, and so look a little different from the pictures which Addo has kindly posted. Overall, it seems I haven't got too much to worry about, so I should sleep a little easier tonight!
If your'e interested, I have taken a photo of the back of two old inner pads and highlighted the piston impression as well as the pin, so you can see how they match up. But I don't know how I can attach it to this forum.
Anyway, the car is driving well with the modified pads, with no braking issues thus far ......
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Re: Citroën Xantia Brake Pads

Post by AceTinker »

Hello again. I have now (hopefully) attached the promised photo where I have white painted the impression left by the piston head and also painted the protruding pin on two old front brake pads. As you will see the alignment is not great but I think it would be just enough to stop the piston head rotating.
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Shows reverse side of 2 old Citroen Xantia Front Brake Pads
Shows reverse side of 2 old Citroen Xantia Front Brake Pads
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Re: Citroën Xantia Brake Pads

Post by Old-Guy »

The crucial point that's been missed is that there are 4 slots in the piston rim and only the biggest one is designed to engage with the 'pip' on the pad - to stop the piston rotating as previously stated. The other 3 slots are there to provide a purchase for tools to wind-back the pistons when fitting new pads.

It's crucial to wind the pistons back until they are flush with the caliper AND with the large slot facing forward horizontally so that the pip slides into the middle of the slot. I've never had a problem and I must have done the job 6 times now on 2 different Xantias.

Getting the pad retaining pins out (or the clips out of the pins), now you're talking about difficult - sometimes....sometimes not.

Interestingly, the pads pictured in the previous post have been incorrectly fitted - indeed look as though they're not the correct pads as the hole (in the pads) for the pad locating pin is within the diameter of the piston and thus the pin must have been missing, which explains how the pips were caught inside the pistons!! :shock:
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Re: Citroën Xantia Brake Pads

Post by Xaccers »

Pad retaining pin????
Got a pic?
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Re: Citroën Xantia Brake Pads

Post by AceTinker »

Who'd have ever thought a set of brake bads could open up such an interesting discussion. Many thanks Old-Guy. I must admit that I can't see that much difference in the relative size of the slots, and need to point out that the locating pins (or pips) were definitely in place when these pads were in, and are still in place on the pads now - I just painted over them. I am assuming the terms 'pip' and 'locating pin' to mean the same thing.

An interesting thought that they may not be right ones for my car, as mine is a non-standard model - it is a 1.9L car with 2.1L discs, and I had a hell of a job finding pads that were the same as those already fitted to it. So maybe these are not quite the right design for my piston heads and the correct ones would be better aligned with the slots, even though these do fit into the brake caliper perfectly??

I think the locating pin you are referring to is the one which slides in horizontally to secure the caliper, and is held there with a small R-shaped pin. Fortunately I have never had any trouble with these, though I would advise anyone fitting these to use brake grease as lubricant, not LM grease as I did, since this just burns down to a dry carbon residue.
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Re: Citroën Xantia Brake Pads

Post by Hell Razor5543 »

I have recently done the front brakes on Gracie, and I did not have any issues with the pip, as I could get things lined up easily.

I would not use anything other than copper slip grease in the area of the brakes, as it can handle extremes of temperature (up to 1200C). Other greases will dry out over time as and when the brakes are used.

Next time you need to get front brake parts you might want to specify brake parts for a 110HDi or V6 Xantia, as these uses the heavy duty brakes. Could somebody with major experience either confirm this is useful or tell me to stop talking utter rot please!

PS addo's picture shows the inside of the piston, and not the head (which is castilated).
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Re: Citroën Xantia Brake Pads

Post by citronut »

Old-Guy wrote:The crucial point that's been missed is that there are 4 slots in the piston rim and only the biggest one is designed to engage with the 'pip' on the pad - to stop the piston rotating as previously stated. The other 3 slots are there to provide a purchase for tools to wind-back the pistons when fitting new pads.
well you learn something every day ( and forget 10 things every day :lol: :roll: :wink: ), i know the BX has indicators on the piston face to show one of two slots which either one must face forward on winding the pistons back, but have not ever noticed any indicator/tion on XANTS ( never had any problems either
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Post by addo »

Old-Guy wrote:The crucial point that's been missed is that there are 4 slots in the piston rim and only the biggest one is designed to engage with the 'pip' on the pad - to stop the piston rotating as previously stated.
In honesty, I was running with the assumption that either people discarded my commentary, or were astute enough to make these observations of detail.
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Re: Citroën Xantia Brake Pads

Post by Old-Guy »

AceTinker wrote:I think the locating pin you are referring to is the one which slides in horizontally to secure the caliper, and is held there with a small R-shaped pin. Fortunately I have never had any trouble with these, though I would advise anyone fitting these to use brake grease as lubricant, not LM grease as I did, since this just burns down to a dry carbon residue.
Just so; but the pin should also go through a hole in the central lug of each pad backing plate - above the white-painted 'pip' in the photos, but absent. The pin also holds the anti-rattle (anti-squeal) shim in place so that it (the shim) applies pressure to the edges of the pads.

I speak from experience only of the 283 x 22 front disc set-up. I don't know if the callipers for the larger 288 x 28 (S1 - only V6. S2 - all HDi 110 & V6, plus 2.0 CT & 2.1 TD after RP 8001) are of a different design - it sounds as though they're the same. So it looks as though those are the wrong pads (no hole).
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