rear caliper touching disc

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bradspau
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rear caliper touching disc

Post by bradspau »

Hi. I have just removed and replaced the rear pads and discs on my 1995 Xantia 1.9TD. I have also removed the caliper from the trailing arm and removed the rust (not much on there though). Copper greased it up and put it all back together. On refitting I have noticed that the disc on the passanger side when rotated without pads in, seems to stick and catch the caliper every full revolution. the drivers side is ok. Pads fitted and road tested and all feels and sounds ok, just a little concerned what would cause the edge of the caliper to touch the disc. Removed and refitted caliper and still the same and as I say, the other side is fine.
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AndersDK
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Post by AndersDK »

You can not check it the way you do.

The disc is only torqued correctly against the wheelhub, when the wheel is fitted and the wheelbolts are torqued down.

The small countersunk screw(s) holding the disc are only there to prevent the disc from falling out or turning, when you fit the wheel.
They must NEVER be torqued, as they are not meant to withstand any forces.
They would shear immediately if you were to rely on them on a braking disc.
If you torque the screw, the disc will most likely sit out of true until the wheel and bolts are fitted and torqued.
Also there are great riscs that the screw will shear.
It should be winded in to sit clear under the disc surface, nothing else. Dont mind the disc sits rocking loose, its meant to.

Be sure that you dont have any debries/rust on the inside of the disc and/or on the hub surface under the disc. This would immediately offset the disc from a square fit.
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bradspau
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Post by bradspau »

hi. I have not torqued or overtighten the disc securing nut. these are new discs do no corrosion. I replaced the disc and refitting the nut. I understand what you are saying though, I suppose the disc does not sit true until the wheels are on and then you cannot see if the caliper is touching..

Will it be ok to leave it as it is ?. I thought I might try it for a week, then take the wheel off and ensure there is no damage or marks on the disc...Just dont want to have to replace the discs again if they get damaged !
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CitroJim
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Post by CitroJim »

When you de-rusted the trailing arm, did you also remove all corrosion from the face of the caliper? The corrosion on the aluminium can be almost invisible and exceedingly hard to remove. It is not easy to spot and equally easy, on first glance to think all is OK.

In the past, I've had to use a cold chisel to remove the corrosion and clean up the caliper face. The caliper, when properly clean, should alow the disc to sit in the middle of the caliper cut-out with plenty of clearance.

You must remove the caliper completely for a proper cleanup. You strictly need a new brake pipe hydraulic seal on reassembly. A proper job cannot be done with the caliper danging off the end of the brake pipe.

A ded give-away that corrosion is present is wedge-shaped wear on the old pads.

I'd not be happy running like this.
Jim

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AndersDK
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Post by AndersDK »

HINT :

Both sides rear calipers are completely identical.
Only difference is the fitting of the bleed screw and the pressure pipe.

You may swap calipers then getting a fresh square flat against the rear arm, ensuring the caliper fits squarely like a new one.
Remember to grease the flat using silver (alu) paste.
The wellknown copraslip (copper paste) is not so good against alu surfaces as it starts off a corrosion by itself, caused by the electrochemical properties between alu and copper.
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Post by Kowalski »

I've had the corrosion behind rear calipers on two Xantias, the thing that fixed it in the end was using wire rope grease between the caliper and suspension arm. Wire rope grease is thicker than treacle and you have to warm it up and apply it with a brush, it stays put pretty well!
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Xaccers
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Post by Xaccers »

Do the fronts suffer from this at all?
I only ask because Cassy's have started being squeeky when I'm travelling a low speeds, definitely the front as they go silent when I pull the handbrake up enough to engage the discs.
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Post by citronut »

no as the fronts are mounted in a diferant way, but you might find you hand brake outter cables are craked were the are flexed every time you turn the steering, this in turn causes the to hold on the brakes slightly

regards malcolm
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