Why is my rear disc brake doing this?
Discussion
I noticed last week my rear disc had a ring of light orange rust on the friction surface nearest the hub.
It wasn't bad but I stripped it down anyway and ran the pads over some sandpaper to deglaze them. I cleaned and copper greased the contact surfaces between pad and caliper. Caliper sliders are free and easy to move and the piston was wound back into the caliper to check it wasn't seized.
I always spray some silver paint on the edges of the disc as it looks nicer than corrosion. Very light overspray went on the friction surface which highlights where the pad is touching - which resulted in that in the picture below.
So why is the pad no longer touching the whole surface? The pads and discs are a couple of years old and show no wear at all.
It wasn't bad but I stripped it down anyway and ran the pads over some sandpaper to deglaze them. I cleaned and copper greased the contact surfaces between pad and caliper. Caliper sliders are free and easy to move and the piston was wound back into the caliper to check it wasn't seized.
I always spray some silver paint on the edges of the disc as it looks nicer than corrosion. Very light overspray went on the friction surface which highlights where the pad is touching - which resulted in that in the picture below.
So why is the pad no longer touching the whole surface? The pads and discs are a couple of years old and show no wear at all.
How many miles have you done since reassembly?
You'll have inadvertently sanded an imperceptibly small chamfer onto the inner and outer radial edges of the pad when you deglazed them which is now causing them to stand off the disc by a few thou. As the pad wears to match the profile of the disc you'll see the contact ring increase in diameter. I wouldn't expect this to take more than 50 miles or so of normal driving.
I've seen this before, don't worry about it.
You'll have inadvertently sanded an imperceptibly small chamfer onto the inner and outer radial edges of the pad when you deglazed them which is now causing them to stand off the disc by a few thou. As the pad wears to match the profile of the disc you'll see the contact ring increase in diameter. I wouldn't expect this to take more than 50 miles or so of normal driving.
I've seen this before, don't worry about it.
It's done about 100 miles since is was put back together. It only used on the motorway though so the brakes don't get used much at all. Pads were put back on the correct side too.
So maybe the sandpaper (even on a flat piece of timber) has actually made them worse...oh well, hopefully time (and distance) will fix it.
So maybe the sandpaper (even on a flat piece of timber) has actually made them worse...oh well, hopefully time (and distance) will fix it.
Sensibleboy said:
It's done about 100 miles since is was put back together. It only used on the motorway though so the brakes don't get used much at all. Pads were put back on the correct side too.
So maybe the sandpaper (even on a flat piece of timber) has actually made them worse...oh well, hopefully time (and distance) will fix it.
Do you have a RWD car? If so, do lots of burnouts, that'll sort it (may need new tyres though...) So maybe the sandpaper (even on a flat piece of timber) has actually made them worse...oh well, hopefully time (and distance) will fix it.
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