Caliper Piston Alignment

[DJGarry]

I've just fitted new genuine front pads to my Bendix calipered Xantia V6. About 8 months ago I noticed a bit more pedal travel than normal and not as sharp braking as when I bought the car after a heavy braking incident. The pads after this looked fine (without taking them out). When changing the pads, I noticed the lug on the outside of the pads and could see one of them had been digging into the caliper piston. Could this of happened as a result of the heavy braking, or would this of been done by the previous owner? Also, how should the four notches in the caliper piston be orientated so they don't interfere with the lug on the pads (not sure I've got mine right)? I've only done around 40 mile since the change, but they seem very spongey, seem to bite a bit harder as the car slows almost to a stop, and on one 9 mile journey, seemed to be binding slightly.
Any help would be greatfuly appriciated.

[AndersDK]

Seems previous owner was not aware that the pad peg (lug) MUST be aligned with <i>either one of</i> the notches in the piston.
If this is not done then the pad would be terribly misaligned.
Note that the piston MUST be screwed in (CW), while pressed lightly. If the piston is forced in, the hand (on XM : the parking) -brake adjuster mechanism located inside the piston will be damaged.
I'm quite sure by your observations - and correctly fitting pads this time - you'll get much better brakes on your XM.

[puddle jumper]

just as a matter of intrest I have three slots with tapered edges and one slot with parallel edges on my piston. I put my new pads in the larger parrell edged slot - is this correct or does it make no diffrence. I thought it looked like the smaller slot had chewed the lug a bit on the old pads I took out.

[AndersDK]

Usaully the piston has 2 parallel slots - one wider than the other, here the piston/pads aligns in the wider slot.
The pad lug must not be a press fit in the slot, as then the pad is misaligned.

[JohnCKL]

Regarding the Xantia brake pads, I was wondering, since the piston exerts pressure on pads when braking, what keeps the pads apart from sticking to the discs when not braking?

[AndersDK]

John -
There are no means providing the pads retracting from the discs, other than the physical contact (actually the centrifugal force) throwing the pads away a wee bit.
The piston is retracted a few 10's of a mm by the lipped bore seal fitted in an angle, thereby allowing the pads to move away.
The pads should have anti-rattle springs fitted, which also helps keep the pads positioned by providing a small friction force on the pad.
All disc brakes works this way.

[JohnCKL]

Thanks Anders, it was the first time that I opened any cars brakes using Haynes instructions. I may have damaged my brake valve when I mistakenly forced the pistons back using too much force and too little turning clockwise. LHM was pouring out from the ruptured brake valve onto the cabin carpet the next day. My mechanic fixed it with a new rubber valve. I've observed only the rear have anti-rattle shims and springs, am I correct?

[AndersDK]

Hi John -
You're right -
No "anti-rattle" springs by common means are found on Xantia front brakes.
Donno if the dust cover insert on the caliper provides a spring force against the pads, it looks like it does.

[Kowalski]

The alignment of the lump on the pads with the grooves in the piston is not imporant except when you need to swing the caliper up / down. The outer piston rotates as it adjusts so any alignment you set it up with to begin with is lost when it adjusts itself.
The inner piston actually applies it's brake force to the lump on the back of the pad.

[AndersDK]

Wot ya mean Kowalski ??
'ya actually mean the pad lug may be allowed to ride on the piston - outside the piston groove ? [B)]
- that is DEFO wrong mate [8)]