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How Do You Know Whether You Need To Replace Rotors?


FAST850R

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Hello,

My car doesn't stop well and I think it's time to replace brake pads.

I already have new set of brake pads so I can remove the old one and compare the thickness, then I am sure I know whether I need to replace them or not.

How about rotors? How do I know whether I need to replace them without taking my car to a shop?

Any tips and advice on it?

Thank you.

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Two conditions for replacement / resurfacing... If your replacing the pads, you should have the rotors resurfaced to remove the surface variability that will most likely be present. An uneven surface will just ware pads out quicker, and if the rotors have warped any, then both sides will not be parallel, which causes other problems. Rotors also have a ware limit. When you take them to a machine shop for resurfacing, they will measure them against the ware limits that are stamped / cast into the rotor. If they are below the ware limit, they are not legal for the shop to resurface, and they should be replaced. Hope this helps...

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You can buy a disc brake micrometer/caliper and check yourself. These have a long "reach" like a C-clamp, so you can get over the lip at the edge of the disk and in to the middle of the working surface to measure. I bought a used one on eBay, but the "home mechanic" grade ones aren't very expensive even new. But I have 3 cars, and many years of doing brakes, so it was well worth avoiding the exercise if they couldn't be machined or weren't thick enough to start.

I've seen posts here that some people just do rotors on every other set of pads. That seems to be close on these cars with factory pads (which are good, but a little dusty). I just replaced my rear rotors and I'm pretty sure it was either the second or third set of pads. The rotors were still legal, but just barely.

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Thank you for the reply.

I guess I will remove rotors and take them to a shop for resurfacing. Any auto shop can do it?

If it's PIA to bring rotors to a shop, I will buy the tool next time.

Most shops that do brake work. Going price around here is $15 each to resurface.

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while you're doing brake work, it's worth it to re-bleed the system with new fluid.

The most influential parts that effect brake performance LOSS on a stock system is old mushy soft lines, and old fluid.

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Yeah, I am still thinking whether I replace or resurface rotors. I haven't decided yet.

Actually, I am more toward to upgrade to 302mm rotors that FCP is selling, if they are worth it.

I also found FCP is selling copper brake lines, are they good?

Any advice on 302mm brake kits or copper brake lines from fcp?

Thank you.

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Hi Coral_t5m,

I need to order bunch of stuff other than rotors so I am ordering from FCP this time.

I decided to order only rear rotors for now because fronts were replaced by PO 2 years ago, and I checked the pads just now, they still have lot of meat left.

Rear looks need to be replaced.

If you give me your shop info such as email address and cel#, I will contact you next time. Next time, I am thinking to upgrade front rotors to 302mm ones.

Let me know what other stuff you are selling.

Thanks.

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Two conditions for replacement / resurfacing... If your replacing the pads, you should have the rotors resurfaced to remove the surface variability that will most likely be present. An uneven surface will just ware pads out quicker, and if the rotors have warped any, then both sides will not be parallel, which causes other problems. Rotors also have a ware limit. When you take them to a machine shop for resurfacing, they will measure them against the ware limits that are stamped / cast into the rotor. If they are below the ware limit, they are not legal for the shop to resurface, and they should be replaced. Hope this helps...

Some argue that a pad burn in (google for directions, aka "bedding" or "bed in") can also accomplish the same thing.

You can eyeball the rotor for signs of cracking, or the development of a 'lip' on the outer edge showing signs of significant wear. Otherwise, ride them till they crack :P

How many miles estimated on these rotors? I'd bet you can replace pads on all four corners, do a burn in and you'll good to go.

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I usually just look at my rotors. If they are seriously grooved out I buy new ones. This is usually the case after one set of pads on the front. Recently I warped my first set of rotors on the 850 ever and cut them myself at work and it worked out great. Took of a little more than 1/10th of an inch off each side.

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