Rust particles on one rear wheel
 

Only happens on the drivers rear wheel, getting rust particles which have to be rubbed of with G3.

Had the pads out the other day and cleaned the disc up as well as painting the hub part and caliper but still rust particles. Brake is not sticking as the car rolls ok and the temp sensor fitted to the wheel matches the other side.

The brakes are not really worn and are Volvo parts, any ideas?

https://photos.app.goo.gl/LxIOT4kDPgxU0Z6y2

Maybe pics would help, as you see one wheel getting dirty with rust. The disc on this side is somewhat not even and has small groves so may be this is the problem?

Will order some new Brembo discs and pads.

Glad you have posted this.

I have the same issue & have never had such a problem on any other vehicle. I only started noticing it as the recent bad weather arrived and the gritters were out so at first I thought it may be a road film residue

My discs are heavily grooved but pads are not worn down. There is no binding of the brakes causing heat to bake the residue on. The rust residue(if that is what it is) has to be removed with fine cutting compound as you have done. Very time consuming.

The vehicle is up for it's first MOT in April and is covered by the Volvo Selekt First MOT warranty. It will be interesting to see if they get changed. If not I'm changing them myself.

Will be changing the discs and pads in the the next week, can not see what else it could be. Is it just one wheel and front or back your having issue with?

Will report back with results.

Both back wheels only so part of me still thinks it is salt/grit residue as the front discs are equally as worn but the front wheels do not have the issue.

It would be good to hear if your situation is resolved by the change of discs and pads.

Mine can not be road grime as it's only one wheel with the issue.

From the photos looks to me like the pad on that disc face is not making contact with the disc properly.
may be you caliper is not free to slide on the mounting pins so is not moving when you brake.

If the pad/disc were making proper contact I would expect to see a clean shiny metal surface

Car had been sat for a day of heavy rain and not driven hence all the discs looked like that.

If you have not used the car for a day or so , the rust forming on the disc is getting rubbed off on first use and discarding ferric oxide on to the wheel rim ..
I have seen similar before when the pads are worn so low that they are grinding metal off the disc .

On one wheel only?