Uneven brake disc wear left-rear wheel
 

I recently changed my rear brake discs and pads, but after some time of driving I noticed some uneven wear on the brake disc on the left rear side:
https://www.the75andztclub.co.uk/for...cbff920217.jpg


Upon noticing this, I regreased the guide pins, caliper, saddle/brake pad carrier and the brake pads and refitted everything, hoping that smooth movement would even out the pads and make my brake disc nice and shiny again.

Unfortunately, this did not seem to work fully. Now, the innermost ring of rust-free brake disc you can see in the picture has expanded somewhat, but the majority of the rust is still there (will make a picture in the morning). Does this mean I waited to long and have to spring for new brake discs? Or can I still work some angle grinder magic (which was also done on my front brake disc) and continue with these - rather new - brake discs?

In time I would expect the disc pad to wear to fit the disc but this is not ideal but the pads could have been made uneven. Is the pad stuck at an angle?


macafee2

After regreasing everything the pad moves freely. Being very fresh pads, there is not much play in the caliper. However, I have no indication that the pad is stuck

Personally i would be removing the carrier and cleaning it, it's quite rusty, and the pad could be getting stuck.
https://i.imgur.com/G3MKLa5l.jpg1

https://i.imgur.com/14z1at0l.jpg2

The caliper can be cleaned scraped clean of rust while on the car, you say you have cleaned the pins did you add some rubber grease to the pins ?
https://i.imgur.com/2KDfyIUl.jpg3

Looking at the caliper, I'd say a good clean of everything is in order, I expect the piston will have picked up some rust.

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Have you still got the old pads ?


What was the wear pattern like on the friction material on the old pads in that caliper. were the friction faces parallel with the pad back plate, like they should be or tapered top to bottom ?


What is the inner face of the disc like ?


Were all the contact, sliding, mounting surfaces cleaned back to bare metal ?

I greased them with Brembo B-quiet grease, as I had that handy already. The pins moved fine through the caliper with the caliper off, but due to the thickness of the new pads the caliper doesn't really move back and forward when it's on.

Cleaned all the contact points except for the piston, did not consider it picking up rust. Will do that next.

Don't have the old pads anymore, but as far as I remember the old disc did not have this pattern of wear

Yes. I forgot to mention this in the first post, and the outside of the carrier and caliper don't look so great, but I did clean the parts of the carrier and caliper that make contact with the brake pads to bare metal before greasing them up. Lifting the caliper up a bit when it is bolted done with the guide pins does suggest that the brake pads are nice and loose from both the carrier and caliper.

Could this be caused by air in the left-rear brake hose, causing the piston to push out a bit less then on the other 3 wheels? Might think too easy on this, but I think the brake fluid is due for a change anyway.

Caliper Piston
 

I had this happen on my front left brake caliper, after pushing the piston back into the caliper and pumping it out a few times, it improved enough to get it through the mot. I removed the piston(s) on both the front and rear calipers and gave them a good clean whilst I was replacing all the brake lines, it's now perfect.