How to tell if rotors need to be changed?

31076 Views 27 Replies 11 Participants Last post by vanhalo, 4 mo ago

doctor33k

Discussion Starter · Aug 21, 2015

I replaced brake pads on both the front and rear wheels of my 2011 w/ 46k miles for the first time today, but I do not know how to tell if the rotors should be changed also.

The dealership told me recently that the rear needed pads and rotors, and that the front just needed pads. However, after taking the old pads off today I could see that the fronts didn't need to be changed and still had a ton of life left in them (probably about 75%), so I don't know if what the dealership told me about needing rear rotors was true or if they were just trying to get a bigger job out of me.

The rear pads were worn low and did need to be changed, but the rotors didn't have any grooves, although there was some rust on the face and all around the outer edge. There did seem to be a tiny lip around the outside, but the wear from the center out until that spot looks like it's worn evenly.

What are good indicators to tell if the rotors need to be changed, and what is minimum thickness of the original stock rotors?

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m998dna

· #2 · Aug 21, 2015 (Edited)

That's too much to think about...

My rule of thumb is when changing the pads turn the rotors once and one time only.. only if they're within tolerance.

But lately I've just been swapping out both the pads and rotors.. Why you ask? I don't trust the auto parts machine shops anymore. Back in the day when you knew who was turning the rotors it wasn't a problem.

Plus I like my rotors cross hatched anyway.

So what happens with rotors? They get hotter, the thinner they get.. then start to warp.

Not worth the hassle to me.. Swap them out when you have everything apart.

.

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RJL1

· #3 · Aug 21, 2015

m998dna said:
That's too much to think about...

My rule of thumb is when changing the pads turn the rotors once and one time only.. only if they're within tolerance.

But lately I've just been swapping out both the pads and rotors.. Why you ask? I don't trust the auto parts machine shops anymore. Back in the day when you knew who was turning the rotors it wasn't a problem.

Plus I like my rotors cross hatched anyway.

So what happens with rotors? They get hotter, the thinner they get.. then start to warp.

Not worth the hassle to me.. Swap them out when you have everything apart.

.

Agreed. I change out the rotors with the pads too. Might as well. Brakes are kinda important.

Reactions: 1

pkai

· #4 · Aug 21, 2015

I agree... swap them pads and rotors at the same time.... Not worth saving pennies...

Once upon a time, disc brake rotors were expensive... no longer.... You're looking at about $150 for all 4..... You can do the whole job yourself for under $200.

Raspy

· #5 · Aug 21, 2015

You shouldn't need to change rotors unless you ran the pads down to where the metal backing scraped the rotor, or if you are getting any vibration or surging while applying the brakes. I have no intention of replacing my rotors unless they are damaged at brake time. Also, if you buy the cheapest rotors you can find, they'll likely warp. So get good ones if you go that route.

Look at the surface and see if it is heat checked or has obvious deep grooving. If not, run them.

My Ram, for instance has 280,000 miles on it with four sets of pads, still the original rotors and they work perfectly. But some Cherokees, for instance, would warp the rotors and they had to be replaced. Also, some manufacturer's, like Ford, don't have tolerance for turning the rotors without going below the minimum thickness. I don't know what the specs are on Wranglers.

Brake shops will likely tell you to change the rotors, but they'll make more profit by selling you new parts whether you need them or not. I had one shop tell me they would not guarantee their work unless they turned the BRAND NEW drums they were installing on my truck. That meant they would probably not be able to be turned again if needed and they could charge me for additional labor.

Run your rotors unless there is an obvious problem.

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Farns

· #6 · Aug 21, 2015

Rotors do go bad by the thickness not being in spec.

Most rotors will have a number stamped somewhere on them describing the minimum thickness. I don't know the specific wrangler minimum thickness. You can use a micrometer to measure the pad contact surface thickness, a vernier caliper will not work because there will usually be a lip around the edge of rotor (which is normal).

Warping (from over heating), deep grooves, and metal on metal contact (neglect to change worn pads) can be fixed by getting the rotor turned at a brake shop (assuming the damage is shallow enough to stay within specified thickness). Thus don't warrant replacing the rotor unless you deem it more cost effective to replace rather than repair.

It is not necessary to replace a rotor at any specific interval. If you don't feel pulses while braking (warped rotors) and there's not a significant lip out the outer brim then just swap the pads and be done. If you really want to, take the glaze off the rotors with some emery cloth to assist in pad break in.

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jac04

· #7 · Aug 21, 2015

sergeantspud said:
If you don't feel pulses while braking (warped rotors) ... then just swap the pads and be done.

Not all pulsing/vibration while braking is warped rotors. Sometimes you will get uneven pad deposits on the rotors, which will cause pulsing. To fix this, you simply need to re-bed the pads. This typically involves a series of progressively harder stops from 60mph to 5mph, then a cool-down period. Cool-down is critical as you must drive around for quite a while with no significant braking until the rotors have cooled down.

I've never changed rotors on any of my cars. I simply install new factory pads - always factory brake pads.

kik

· #8 · Aug 21, 2015

Back in the day we had them turned/cut, now when I do brakes I use new rotors. They're inexpensive enough and by replacing them that's one less component to be concerned about.Your choice. If there's no damage you could do them every other time you change the pads. I prefer not to wait.

Wharfrat

· #9 · Aug 21, 2015

I put new ones on every time but every other time is reasonable if there is no obvious damage or excessive wear.

Freedom JK

· #10 · Aug 21, 2015

I usually change my rotors every other brake pad change. If you feel some vibration in the steering wheel when you apply the brakes then your rotors are warped. If they do not vibrate, then they are straight. I would replace them if they are warped. Having the rotors turned will get them straight again, but it also makes them thinner and more susceptible to warping again sooner. And, rotors are not too expensive, like $37 each for good OEM quality rotors.

Farns

· #11 · Aug 21, 2015

I'm surprised at all the "replace every brake job" responses. What is it that makes new rotors "one less thing to worry about"? In the 4 years I worked at a brake shop never had I seen catastrophic failure of any rotor. Replace them when they show signs of needing to be replaced. If you love throwing money at your jeep at least throw money at something that will be beneficial.

Reactions: 1

m998dna

· #12 · Aug 21, 2015

sergeantspud said:
I'm surprised at all the "replace every brake job" responses. What is it that makes new rotors "one less thing to worry about"? In the 4 years I worked at a brake shop never had I seen catastrophic failure of any rotor. Replace them when they show signs of needing to be replaced. If you love throwing money at your jeep at least throw money at something that will be beneficial.

Who's talking catastrophic failure?

Time is money.. and when you're doing your own brake jobs it's better and easier to swap out the rotors... otherwise you need to have the Jeep up off all fours and take the rotors down to be turned. Then you need another vehicle to get them down there and pick them up...

Pretty simple concept..

.

Reactions: 1

pkai

· #13 · Aug 21, 2015

sergeantspud said:
I'm surprised at all the "replace every brake job" responses. What is it that makes new rotors "one less thing to worry about"? In the 4 years I worked at a brake shop never had I seen catastrophic failure of any rotor. Replace them when they show signs of needing to be replaced. If you love throwing money at your jeep at least throw money at something that will be beneficial.

I don't think they mean "worry" as in the thing is going to fly apart....

I look at it this way.... pay $15 to have a rotor turned or pay $30 for a new one. To me, that's a pretty big DUH!

Raspy

· #14 · Aug 21, 2015

m998dna said:
Who's talking catastrophic failure?

Time is money.. and when you're doing your own brake jobs it's better and easier to swap out the rotors... otherwise you need to have the Jeep up off all fours and take the rotors down to be turned. Then you need another vehicle to get them down there and pick them up...

Pretty simple concept..

.

If time is money, and you want to keep it simple, just re-use the rotors you already have. Don't turn them, just replace the pads and be done with it. If there is nothing wrong with them, don't try to fix them and don't throw them away.

That is the simple concept.

Farns

· #15 · Aug 21, 2015

I completely agree with the replace vs repair argument. But they don't need to be replaced every brake job just as you wouldn't replace the oil drain plug every oil change. Replace when it's broken, you don't gain anything from replacing lightly worn rotors.

Raspy

· #16 · Aug 21, 2015

kik said:
Back in the day we had them turned/cut, now when I do brakes I use new rotors. They're inexpensive enough and by replacing them that's one less component to be concerned about.Your choice. If there's no damage you could do them every other time you change the pads. I prefer not to wait.

One of the reasons I don't replace them, unless they are damaged, or rumbling, or pulsing, is that new rotors come in all different quality levels. If you go cheap and think it's "one less component to be concerned about", or you want to "save pennies", you may find the new ones warp and then have to be replaced again with better ones. By then the perfectly good ones you threw away are long gone and your "cheap" insurance proves to be a hassle.

I suppose we could all replace the wheels every time we replace the tires or replace the gas tank every time we need gas, but at some point, why?

But it's your Jeep, if it makes you happy, do it.

kik

· #17 · Aug 21, 2015

Raspy said:
One of the reasons I don't replace them, unless they are damaged, or rumbling, or pulsing, is that new rotors come in all different quality levels. If you go cheap and think it's "one less component to be concerned about", or you want to "save pennies", you may find the new ones warp and then have to be replaced again with better ones. By then the perfectly good ones you threw away are long gone and your "cheap" insurance proves to be a hassle.

I suppose we could all replace the wheels every time we replace the tires or replace the gas tank every time we need gas, but at some point, why?

But it's your Jeep, if it makes you happy, do it.

Who criticized you for not replacing your rotors? If that's your choice that's fine. And, what makes you assume that I don't use high quality replacement rotors that are of superior quality to Chrysler OEM rotors in any of my vehicles? I know that I never mentioned using "cheap" components. That's another one of your assumptions. If it makes you feel better to be sarcastic that's fine too, but it doesn't answer the question. It gives one opinion which is also fine. Just like based upon my experience, I gave my opinion. I don't do anything cheap with my JK so if you prefer to make those assumptions then that's what is, another assumption. You're correct it does make me happy to use superior parts for my JK. Re-read my post. All OEM parts that Chrysler uses aren't necessarily the highest quality parts that are available. But, like anything else it's an individual choice.

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m998dna

· #18 · Aug 21, 2015 (Edited)

Raspy said:
If time is money, and you want to keep it simple, just re-use the rotors you already have. Don't turn them, just replace the pads and be done with it. If there is nothing wrong with them, don't try to fix them and don't throw them away.

That is the simple concept.

OK .. whatever you say. I bet you're one of those guys that when swapping out a clutch you leave the old flywheel in there..

This is why some mechanics need to be supervised..

.

Raspy

· #19 · Aug 21, 2015

Kik,

Not being sarcastic at all. Just curious.

Not you, but another poster talked about saving pennies and rotors are so cheap. Just looking for a real mechanical problem with re-using rotors and I haven't found one, so wanted to tap into your expertise as to why you would be "concerned".

Sorry you misunderstood.

Raspy

· #20 · Aug 21, 2015

m998dna said:
OK .. whatever you say. I bet you're one of those guys that when swapping out a clutch you leave the old flywheel in there..

This is why some mechanics need to be supervised..

.

Oh, it's even worse than that! I always insist on re-using the old throw out bearing and input shaft bearing too. Love the scraping and chattering! Cracked flex plates are another one of my favorite things to re-use.

I also have the audacity to ask others "why" they do things. Gets people riled up though. :happyyes:

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