FAQs—Mini Brake Disc
- When is it a good idea to resurface the brake disc/rotor?
If the disc/rotor has scores, rough spots, or hollowed parts, resurfacing should be considered. And if the grooves or scores are more than 0.060 in. or 1.5 mm. deep, disc resurfacing is advised to prevent brake failure and inefficiency. It’s also a good idea to resurface the disc if runout has exceeded the specs, if there’s extensive corrosion on the rotor, or if thickness variation is over 0.001 in. or 0.025 mm. You have to check the minimal thickness allowed for the disc to see if resurfacing can still save it or if it really needs to be replaced. The disc can’t be too thin. Otherwise, this will lead to extensive rotor damage and dangerous braking. Also check for runout specs and use this as a guide.
- Why do most mechanics prefer replacing a warped brake disc instead of turning it? What’s a good reason for this? Can’t a warped rotor be fixed by turning?
Warped rotors/discs may already be thin; that’s why most mechanics would rather replace them in case of warpage. Turning them may work for a while. But if they’re already too thin or about to hit the minimum thickness required for brake discs, then turning wouldn’t be for the long term. It’s easier and far better to turn scored discs than rotors damaged through warpage.
- How will I know if the discs are already too thin that turning shouldn’t be done anymore?
You should look for the specifications for minimal thickness so that when you measure the rotors/discs, you’ll know if they’re within the spec or close to crossing the limits. You can find this information stamped on the discs. Or, you may check out the specs through your service or vehicle manual. If the cracks or grooves are already too deep, don’t take a risk. Turning isn’t your best option.
- A friend of mine had his brake disc/rotor turned because of uneven wear. The mechanic I paid to check my brakes said that my brake disc should be replaced because of uneven wear caused by hard spots. Is this a good call? Why not just turn the disc?
Turning the disc/rotor is one way of fixing uneven wear. This is done to solve runout problems. Unfortunately, when this type of wear is caused by hard spots, it’s better to just have the disc replaced. The same problem may resurface eventually even if the disc is turned since hard spots cause changes that get deep into the surface and beyond. If you just cut off the top or some parts of the disc, this will be just a temporary fix at best. This is not the best solution.
- Is it really required to turn or resurface the brake disc when changing the brake pad? Or is it just a scheme so that we’ll pay more for the brake service?
Brake discs don’t always need to be turned, especially if they’re still in good working condition or only have slight grooves. However, mechanics take all the right measures during brake pad replacement to make sure that the customer won’t have to come back for another brake service should their brake disc fail or get damaged severely after some time. They want to prevent any brake problem in case the brake disc is already showing forms of damage, even if they’re still working. By having the old rotors turned (or replaced, if needed), good surface finish will be achieved. This will help with the break-in of the pads and will ensure the desired braking performance. If the brake discs are scored or damaged and they’re not changed along with the pads, braking power and efficiency will suffer. This can bring about other braking issues or poor braking performance.
- I checked the brake pads and discs of my Mini. I found some minor cracks on the disc surface. Does this mean that it’s time to replace the brake discs?
It’s not unusual to find some cracking on the brake disc since this is caused by wear and exposure to heat. However, if the cracks are deep, like more than an inch, the disc should be replaced. Deep cracks can lead to disc failure or poor braking performance.
- There’s uneven wear on my brake disc and the mechanic blames it on excessive runout. Is there a way to minimize runout? What are the solutions?
Re-indexing the disc’s spot on the hub can be done to minimize runout. The disc is moved from its former position over 1 or 2 bolt holes or whatever is needed. As runout is measured through a dial indicator, necessary adjustments should be done to make sure that you’ll get the least runout or that it will be within the specs. If it turns out that runout has exceeded the limit, a correction plate may be used. This will be placed between the rotor and hub flange.