Xantia rear brake

[xf1ref]

Hello all,
What is the role for the sheet metal from xantia rear brake pads? Two year ago I cleaned the calipers for oxide and I mounted the new pads without those sheet metal . After some time I decided to put back the sheet metal and yesterday when I checked the brake pads were worn unequal on lenght...I think because of those sheet metal.
And a second question: What should I use to protect the calipers from oxide? I used a lot of grase but after some time...two years for example...the oxide begin to appear again.

[Hell Razor5543]

Those are shims, and are used to counter any uneven calliper issues. It could be tricky getting them back in the correct positions.

I intend to use grease proof paper between the calliper and trailing arms next time I have to take the callipers off.

[citronut]

the shims are anti squeal ( supposed ) nout to do with pad wear

[Hell Razor5543]

the shims are anti squeal ( supposed ) nout to do with pad wear

Sorry, my bad.

[xf1ref]

From my point of view, when those shims are in place, the caliper piston press harder on half pad ...there where shim make contact with the piston. That why I belive my pads are worn harder at one end...but I'm not very sure
I was thinking to paint the caliper on side were make contact with the arm...or something else to seal the aluminum surface of the caliper from air, water and others.

LE: Thanks citronut for answer. Rear brakes make no sound with or without those shims. Should I mount them back?

[Mandrake]

As citronut says, they're anti-squeal/chatter bias shims.

They are positioned such that more pressure is applied on the trailing side of the pad rather than the leading side of the pad - this is to prevent the leading edge of the pad digging in and squealing/shuddering when the pads wear.

They have to go up the right way - if you get them upside down the brakes will be more prone to squealing than without them as the leading edge of the pad will dig in.

[xf1ref]

I found this picture. Is this the right position for shims..for both of them?

[Mandrake]

That looks right, yes. The metal side faces down and the void is at the top.

If you think about the forwards rotation of the wheel when the brake is applied, the bottom of the pad is the trailing edge of the pad.

[xf1ref]

Thank you all for answers! Next week I will buy new pads for rear brakes and I will mount shims in the right position.
Honestly, I belive that until now the shims have been mounted upside down

[Mandrake]

I've seen one of the four shims mounted upside down on a previous Xantia of mine when I bought it - and that one pad had unusual wear compared to the other three such that the pad surface was no where near parallel to the backing plate. So the shim being upside down definitely affects the wear pattern of the pad.

The leading edge of the pad (which the upside down shim was applying more force to) was much thinner than the trailing edge. Normally the pad wear should be nearly parallel, or slightly thinner on the trailing edge. It also squealed intermittently - that's what made me investigate when the brakes were otherwise working fine.

In the short term I swamped the shim around the right way and the squealing immediately stopped. (Later on I replaced all the rear pads)