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What's up with this rear left/pass rotor? I just finished front and back rotor and pad replacement and conducted the bedding process. All surfaces were clean with brake cleaner and only pad grease was used on the back of the pads. The other 3 sides bedded normally, but I haven't seen anything like this one before. I ran my fingers over the two surfaces (after it cooled down, of course) and it's flat. No grooves or perceptible difference in texture. Any ideas?
Sidenote (install notes):
- I just got the car 1.5 months ago and one of the previous owners rounded off the guide pin bolts (rear). I had to hammer a 14mm wrench to tighten them. What a bugger.
- The same rear right/pass brake piston was extended all way out even though I released handbrake - the caliper tool wouldn't even fit in there with the backing plate, so I had to bleed brake fluid, then twist and push with the tool. Could it be hill holding being activated at some point?
- While the front Brembos were the quickest brake job I've ever done, the rear have got to be the hardest - (a) the pistons have to pushed back ALL the way in order for the caliper bracket to fit over the new pads; I've never seen such tight tolerances; (b) those seemingly rounded off (between 14-15mm) guide pin bolts were a pain in the butt! Even my Audi D2 A8s were waaay easier.
What it looks like is the inner diameter of the rotor is corroded; this means the pad is not making contact ... contact that normally cleans off any corrosion.
"All surfaces" were cleaned with brake cleaner? Does that include the pad surfaces?
Why didn't you replace the bad guide pins? If you can afford new rotors and pads, you can afford new guide pins so you can properly torque them.
MINI's don't use a separate pad on the inside of the rotor for the parking brake; they use the same pad that provides normal stopping action. As the pads wear, the piston turns and extends to take up the clearance. When you install new pads, the piston has to be threaded back into the bore in the caliper. Did you reset the rear caliper pistons when you installed the new pads? The rear pistons are threaded, and there is a special tool you need to reset them. The procedure is detailed in the Bentley service manual.
Yeah your pads are shot or the outer pad has separated from the backing plate. That has been know to happen with EBC pads before.
Buy new pins, take the wheel off, remove the caliber and look at the pad. See if you still have the whole pad on the backing plate. See if the pad wear is even and see if the outside pad was seated correctly.
When done put the new pin bolts in and torque them correctly.
To clarify: this photo was taken half an hour (yes, 30 minutes) after got back from my bedding-in drive today. No way corrosion can happen that quickly. Could it be staining of some sort (and yes, I cleaned the pad contact surface with cleaner)? The pads I installed were painted/stained black on the back and edges and I noticed that a couple of the new pads I installed (but didn't think much of it at the time) had some black paint over sprayed on the pad material itself. Not much, just a little.
Secondly, I'm aware that pistons will push in as pads wear, so that's expected when I was going to replace them, but the piston in question (right rear) was extended almost all the way out. I know they weren't that way when I removed the pads and cradle (I went back in the house and came back out to see it that way), mainly because (a) the pads are only halfway worn (I just thought I'd swap new ones to match rotors); and (b) the left rear piston was normal.
In terms of the guide pins, I honestly wasn't prepared for it, so it'll be on my replace list when the next pad job comes, which should be soon since I'm planning to hit some AutoX this season.
Your outer pad is not flat to the rotor surface. That is why you have rust. You heated the rotors and a little water got on the bare rotor and caused the rust. Take your car out again and go for a short ride and lightly pull the emergency brake a few times and release it.
If the pad makes full contact across the rotor surface it will remove the surface rust quickly.
This is common where I live because of high humidity. Hot rotors surface rust quickly right after the car is parked.
Your outer pad is not flat to the rotor surface. That is why you have rust. You heated the rotors and a little water got on the bare rotor and caused the rust. Take your car out again and go for a short ride and lightly pull the emergency brake a few times and release it.
If the pad makes full contact across the rotor surface it will remove the surface rust quickly.
This is common where I live because of high humidity. Hot rotors surface rust quickly right after the car is parked.
06-05-2018, 05:17 PM
