Rear brake pads making minimum contact.

[fastandcurious]

When I took my car for MOT last, It failed on the handbrakesurprise surprise. It was also pointed out to me that the pads were only making contact on the out side of the disc and the inner sides had become corroded. This showed up as a poor reading on the brake test. I removed the discs and cleaned up the inside surface as there was still adequate thickness and replaced the half worn pads. After backing off the adjustment on the handbrake it worked again, so I went for the retest which it passed fine. Although I haven't done many miles since then, the offside rear disc still feels rough to the touch. Is it caused by a sticking piston, if so why does the outside of the disc get contact but not the inside when the piston comes from the inside of the caliper? F&C

[Bluebottle]

The caliper that holds the brake pads is self centering. As the piston pushes the innner pad out to make contact with the disk, when cantact is made the outer pad (caliper) get drawn back in until the pad touches the disk.
If you have a smoother outer side to the disk it would indicate that the outer pad is rubbing the disk when the brake pedal is note being applied. This is probably caused by calliper not being able to slide freely on its guide pins.
If the little convoluted gaters come off, dirt can get into the giude pins/bores.
I Would suggest dismantling the caliper and cleaning it all. If the guide pins are badly scoured you will need to either replace the calipers (you can get recon calipers cheaply £70 ish) or refurb kits £15.

[AntonyJ]

This can also be caused by the cylinder not being lined up to the pad properly.
The pad has a nipple on the rear that must sit in one of the four "hole" on the piston.

[GreenV8S]

Check for equal pad wear on the inside versus the outside, and confirm that the pads are wearing more or less flat.

If the pads are significantly tapered or wearing unequally it indicates that the sliders are worn and/or sticking.