When the COVID lockdown hit back in March, daily commuting stopped, kids were pulled from school, shopping essentially stopped except for weekly trips to the grocery store, and the BMW wagon went from use 4 to 6 times a day to a couple times a week. The drop in use was dramatic, and one result of this was a couple of instances of the brake pads bonding to the rotors with corrosion. You would go to use the car, all the brakes would be stuck, and after a few seconds of throttle, eventually the corrosion bond would break and the car would start rolling normally.
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BMW E61 535xi Front Rotor
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Use of the car has gradually returned, and we did a local road trip in August. The brakes in the car were completed replaced
when I did the turbo project 2 years ago, since then the car has only travelled about 20,000km. During the road trip I noticed minor brake pedal vibration - more apparent during light braking, less apparent with a bit more force on the pedal.
When I brought the car into my garage in September
to look at the low boost pressure issue, this was on my list of issues to repair.
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| Rust ridges on front rotor left from pads freezing to rotor |
I thought about purchasing new pads and rotors to sort out the issue, but 20,000km is next to no use, and I wanted to avoid the cost and the waste. I got onto google and looked for brake rotor turning services. At one time this was common, now, almost impossible to find. There was one machine shop in east Montreal that gave me a reasonable quote for turning the rotors, but when I went to drop them off, the machinist had sufferred an accident and would be off work for a month. No go.
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| Frozen brake pad prints on the front rotor |
So - if a part is broken, you can't really break it any more trying to fix it. I decided to try sanding the rotor surfaces with a Dewalt 5" orbital sander with 200 grit paper, to try to remove the ridges.
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| Frozen brake pad prints on the front rotor |
I sanded the complete surfaces, front and back, of both disks. I did two passes, not wanting to remove too much material and creating a bigger problem than I already had. I was careful to spend the same amount of time and pressure as equally as possible around the surface of the disk, just spending slightly more time on the ridges left by the various brake pad prints on the rotor surface. I didn't try to completely remove the brake pad prints, but smooth them out and hopefully reduce the pedal vibration.
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| Front disc following sanding - pad outlines are still visible. |
The sanding removed some of the ridges left during the pad bedding into the rotors. I knew that the pads would have to bed in again, so I was patient for the last month and tried to modulate my brake pressure to allow that to happen gradually.
I would say that this has largely solved the problem, although, with very light application of the brakes there is still a slight vibration. With normal stopping pressure, the vibration is not apparent. It seems to have improved the braking feel, but it's not perfect. It seems to be improving with time however, so I'll let it go for another month or two and report back whether the problem resolves itself. For now - I've saved the cost of a pair of rotors and pads. So far, so good.
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