Newton's third law takes a holiday - Clanger
MoT time came round recently and I found myself at the test station in a pit with the tester looking at the Synergie's brake disks. The Lucas brakes have a single piston in a floating caliper. The rods on which the caliper floats are shiny, greased and protected by intact gaiters, and the caliper can be moved easily when the pads are withdrawn. The pads were not siezed in the caliper but that shouldn't matter given that the caliper floats.

Why was the outside face of the disc immaculate and shiny and the inside two thirds of the disc surface rusty and pitted? There is an obvious implication that more effort is being applied to the outside of the disc to keep it so clean, but why?

I've been spannering cars in an amateur way man and boy so I'm not surprised, just curious.

Any genius out there know what is going on?


Hawkeye
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Stranger in a strange land
Newton's third law takes a holiday - LHM
Perhaps the caliper is not sliding exactly at right angles to the disc surface?

I have also come across uneven disc surface wear with 'floating' calipers, and it's usually been accompanied with the pads wearing at different rates.

Can't say I'm a fan of these calipers, and prefer the older 2- or 4-piston assemblies with the caliper bolted to the stub axle (or, in the case of the Citroen CX, actually part of the stub axle!).

I guess the outer surface is designed to wear nice and shiny to look good through the wheels!!
Newton's third law takes a holiday - J Bonington Jagworth
Does the pad wear corroborate? It may just be that the inside of the disc gets a lot more water thrown at it - although we haven't had much here lately, I have to say.
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Illegitimi non carborundum!
Newton's third law takes a holiday - Cardew(USA)
Some grit trapped between a pad and disc??
Newton's third law takes a holiday - Aprilia
Is this one side, or both?

You sound intellegent enough to know that something must be wrong. These are the so-called 'Collette' calipers and when working properly the same force *has* to be applied to both pads.
The most likely explanation is that there is something wrong with the slide mechanism. If there is too much free play in the slide then the inner side of the caliper can 'hinge' away from the pad - the result being that most pressure is at the outer edge of the pad, with little at the inner edge. This gives the symptom you describe.
Newton's third law takes a holiday - martint123
I found on the old Renault that if there was any wear on the slider s then the caliper twisted ever so slightly when the brakes were applied and stopped sliding. The rusty disks (not the piston side) was more noticable with my short commute with little braking - and the little braking was gentle rather than heavy. A blast down the backroads with heavier braking cleaned the disks up fine. After having to change disks every year or so (for rust) I found that heavy braking seemd to sort them out.
Newton's third law takes a holiday - king arthur
Pads fitted incorrectly perhaps?
Newton's third law takes a holiday - Clanger
Thanks for your replies.

Aprilia, both sides. You may have it in that perhaps the floating is too easy with the play allowing the caliper to turn slightly as braking effort is applied.

Am I going to do anything about it?
Not as long as the car stops as well as it does and spins the needles on the MoT brake test machine.


Hawkeye
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Stranger in a strange land
Newton's third law takes a holiday - M.M
H,

Very common with the vehicles I see, even when there isn't a problem with seized pads/calipers.

Just looked at the discs on the scrap pile and 60% show more corrosion on the inner surface.

M.M
Newton's third law takes a holiday - J Bonington Jagworth
"more corrosion on the inner surface."

Because that's the side exposed to all the crud thrown up by the opposite wheel (and the traffic in front).
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Illegitimi non carborundum!
Newton's third law takes a holiday - M.M
JBJ,

Possibly....but some of these are Citroen rear discs that have a complete metal "cover" that keeps the road dirt out and they are just the same.

I accept it, don't worry about it but it is odd.

M.M
 

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