Motor Vehicle Maintenance & Repair Asked by C.List on January 12, 2021
Our car has only about 22k miles on it, but it’s always been kept outside (in NY) and went for several months this winter with no use. This summer, we developed a low grinding sound when braking. A visual inspection shows there’s still a lot of brake pad left, but the rotors are seriously scored with grooves and rather rough to the touch. The rear ones are worse than the front and the sound seems to be coming from those.
My question: should I just live with them as they are until the rough rotors wear the pads down and then replace everything, or should replace the pads early and get the rotors ground?
I know this is long ago, but people will view this thread, so I thought I'd post an answer.
Problem is your caliper needs to be rebuilt or replaced.
Internally, the caliper piston will gum up/varnish over time, and the square-cut seal becomes brittle or fatigued. As a result, the piston will start to become sluggish and won't return properly when you let off the brakes, causing the brake pad to ride the disc. This failure/maintenance requirement is inevitable, but is greatly accelerated by overheating the brakes.
I'm guessing you noticed some shimmy on breaking after you've been driving for a while too, which happens because the rotor heats up too much when the pad isn't releasing fully off the rotor. Failed caliper piston return also causes the brake pads to wear unevenly, with the inner pad wearing much faster than the outer one.
If you're experiencing repeat uneven brake pad wear and shimmy on braking, it's likely you should replace the rotor too, even if it's not scored. Oonce it's been overheated several times in the past, it will continue to "re-warp" once it gets hot, even at normal operating temperatures. That will cause the shimmy, denature the lubrication on the slide pins, cause the pads to wear unevenly All that will overheat the caliper further, which will then cause the caliper piston return problem to reappear. Turning the rotor won't help, either. A new one that has never been overheated won't warp when it gets up to hot operating temperature like a previously overheated one will.
On the caliper, everyone likes to just replace the caliper, but cleaning, lubricating, and re-gasketing a caliper (aka "rebuilding") is easy as can be, way cheaper (like $8 instead of $100), and keeps things out of the landfill. It's not really necessary to hone the cylinder when rebuilding a caliper because if it's rusted or pitted, you should just replace it. So if you find the piston or cylinder is pitted, forget it, buy a new caliper!
You should also change your brake fluid, because it's also been overheated.
Hope this helps!
Correct answer by Justin Wilson on January 12, 2021
If the pits are really deep, then grinding may not be an option - there is normally a minimum thickness specified.
I would suggest that you save up for the new pads and rotors and change them when ready. That is ONLY if the existing ones are stopping the vehicle as they should - a bit of extra noise is not an issue as long as the stopping power is there.
Answered by Solar Mike on January 12, 2021
So this question has been viewed a lot and I wanted to post a followup: I ended up replacing the pads all around, and the rotors on the left side of the car that were really pitted (rotors on the right side were totally smooth) - this was at about 24K miles. Just now, at 45K miles, I got a break pad warning light on the car. Since I had to take it in for regular service, I asked them to check it out since it looked to me like all of the pads still had wear on them, but I was noticing the same sort of un-even scoring ont he rotors that I'd seen before.
The dealer said the pads were worn down on the hard-to-see (and hard to feel) inner side of the rotors and the rotors were once again worn very unevenly to the point that they should be replaced. I told them to go ahead, since I didn't have the time to do the job again. This seems super-excessive to me, and really weird - I've never seen this before in my 30 or so years of car ownership and DIY mechanic-ing. Then again, there are times of the year where this car goes for days to weeks at a time without being driven. This last time was the first time I have ever had someone other than myself do the brake maintenance on a car - since it's such a simple job.
Note that the car is a 2014 BMW X3, and has otherwise been fine.
...very weird. I will probably be trading in the car in the next 12 months and I'm looking forward to not having to worry about it.
Answered by C.List on January 12, 2021
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