Rear Discs - Problem

[skiptontweed]

[see picture]

The rear discs on my 172 Cup have done this on both driver and passenger sides, on the outboard face of each disc. The picture shown is after 5k miles in 3 months on new discs and pads.

This is the third set of discs that have done this, all with brand new pads. the calipers appear to operate freely - they dont appear seized.

Any ideas what might be causing this?

 

[uly8]

what's the problem? :S

 

[Sym0n]

Are you rolling with OEM discs and pads?

 

[skiptontweed]

Cheers for the quick responses

The 12mm lip of unused friction surface on the outside of the disc is irritating me - Im worried it will get worse.

Im running OEM discs and pads. Any thoughts?

 

[uly8]

ahh right

i've got a 172Cup and mine are worse than yours... it's just the way they are.

 

[uly8]

i'll take a picture of mine, so you can see you're not alone

 

[Sym0n]

Have you checked to see that the pads are in full contact with the discs, from that picture I'd suspect not or possibly that they are the wrong size. I'm pretty sure from the pads I've just fitted to the new rears on my Ph1 that the pad is the full size of the face of the disc.

Did you wind the piston all the way back and push the caliper tight towards the piston after fitting the pads and discs?

(I am guessing btw).

 

[skiptontweed]

cheers,

I was looking at a 182 yesterday and its rear discs were fine - the entire friction surface was being used. I think if mine gets much worse then it will fail its MOT.

Is there any reason why I cannot fit 182 rear calipers? I think they are the same but there may have been a subtle mod to fix this?

 

[skiptontweed]

Have you checked to see that the pads are in full contact with the discs, from that picture I'd suspect not or possibly that they are the wrong size. I'm pretty sure from the pads I've just fitted to the new rears on my Ph1 that the pad is the full size of the face of the disc.

Did you wind the piston all the way back and push the caliper tight towards the piston after fitting the pads and discs?

(I am guessing btw).

Hi, yes the pads cover the entire width of the disc. I wound the pistons all the way back into the calipers to check they were free.

 

[Sym0n]

Just taken now, hardly covered any mileage though but you can see full friction on the face.

 

[skiptontweed]

Thanks for posting the pics - yours look fine!

Even after the first drive my problem was obvious. I suspect the calipers are to blame.

 

[Ralphizzle]

Hmmm...

Funny! My rear rotors look like that too.
Thought it was normal?

 

[mark123]

It's because it's a 172 cup mine are the same. They don't do enough to clean up the discs properly and once that corrosion starts it's difficult to clean off. Just leave them until they fail them at the MoT.

 

[calum001]

well mine are exactly like that (a bit worse actually) and ive got a 182 ??

 

[mark123]

Just happens quicker on a cup.

 

[Henry]

the rears on mine are swept right to the edge and are (i suspect) the original discs (on 60k). i'd not really worry about it, but you could remove the pads to see if they've crumbled at the edge, file the lip off the disc, lube the caliper up, and see what happens. think it's because they do little work at the back - everything becomes 'lazy'; giving the brakes a good workout periodically might help