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Discussion Starter #1
We have a strange grind sound that only happens when making a hard stop. Can't tell if its from the front or rear but my guess would be front. The car only has 40k miles. When we got new tires a few months ago, the tire store tech called me over to show me the front calipers and based on his view of the distance between the front of the caliper bracket and the rotor it needed new pads. I could see that it looked like the bracket was almost sitting on the rotor. I should have asked him to measure the pads. He said the rear pads were ok. The rotors were not scored nor are they warped. Slow to moderate stops are firm and quiet.


Now, I was into the Hyundai dealer last week for some other work and he apparently did measure the pads and he said they were only in the "yellow" category on the safety report. He said I'd be good till the next service interval. I think he mentioned 5mm thickness? I told him about the grinding and he didn't know, said maybe its a hub.


The noise that happens on a hard stop is a metal grinding sound. So who do I believe? Could it be another part besides brakes?
 

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Pads may have worn sufficiently that the brake wear tab is now contacting the rotor. This is designed to alert the driver that pad replacement is imminent.
 

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5mm is 1/2 of original pad thickness new in box.. grinding sounds when on pedal for hard stop,, could be simple friction co-efficient mis-match between pad material and friction face of rotor,, or pads riding rust rings (usually seen at inside face of rotor,, or rotor face look like alligator hide for rust

Need little better visual to see what going on
 

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Discussion Starter #4
The wear tab wouldn't be contacting the rotor, its not squealing. Those wear tabs make it squeal but when you step on it, then it goes away because the caliper shifts position, right? The friction surface of the rotor does not look rusted or scored but now that you mention it I think there is a rust ring near the inner or outer edge of it. I'd have to take a closer look.
 

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Pads are cheap. I have seen many cars wear one pad more than the others and also wear at an angle. If you know what your doing remove the pads from the wheel that's making the noise and have a real look. The rotor surface would also have some damage if the pads are metal to metal. What sbr11 said about coefficient problems yea been there on many occasions with aftermarket pads and believe me theirs no cure but to try another brand.
 

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Discussion Starter #6
Well....just to follow up: the grinding when hot got a little worse so we took it to the dealer as they have a competitive price on brake service of $199. I figured that would be great and we'd get some OEM pads which gave a good life. You would expect to get Hyundai parts at a Hyundai dealer but....they put on Autozone pads. I could tell from the part number that was not a stock number and when I asked I was told they're Duralast, which is Autozone's brand. Specifically, they're the Duralast Gold Ceramic.

Now, after a hundred miles or so, I notice they are very noisy when they get hot after driving for a while. Like a squeal. Are ceramic pads supposed to squeal? Maybe they forgot to lube the back plate...we are going to take it back. I'm not sure at this point whether to blame cheap aftermarket parts or incompetent service. Those factory pads never made a sound at all until they wore thin.
 

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Usually it's incompatible materials (ie cheap pads and rotors) and/or lack of lube on metal to metal contact areas. I've done OEM pads with Advance Auto Plat rotors; 20k and no noise or other issues. Have done cheap pads and no lube before and paid for it with squealing excessively.
 

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Did they machine the rotors or just fit pads. Most pads will be OK if the rotor is machined. When new pads are bed in a layer of pad material is deposited onto the iron rotor surface creating compatibility with the materials. If it's not done it may make squealing/grinding noises when barking sometimes hot/cold hard/soft braking. I'm interested in what the dealer excuse will be.
 

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Discussion Starter #9
Did they machine the rotors or just fit pads. Most pads will be OK if the rotor is machined. When new pads are bed in a layer of pad material is deposited onto the iron rotor surface creating compatibility with the materials. If it's not done it may make squealing/grinding noises when barking sometimes hot/cold hard/soft braking. I'm interested in what the dealer excuse will be.
Yes, the rotors were machined. How long should it take to bed in?
 

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To bed in the brakes you accelerate to around 60kms/37 mph then lightly brake to an almost stop then accerate back up to 60 and repeat for 8 to 10 times. This should have been done by the mechanic during the test drive. After that you brake normally so I suggest you take it back and have them test drive with you in the car to point out your concerns.
 

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The pad wear tab is on the pad, so if it contacts the rotor, it will continue to do so under braking. Also, rotors shouldn't be machined as it will take the thickness under tolerance 99.9% of the time.

Bedding in is a waste of time and destructive to both the rotor/pads. They even have bedding instructions in the pad box, but have never done it on mine or any other cars, no problems. Think about the millions of new cars sold, no bedding and they are fine.

When the noise (squeal) is heard, hit the brakes harder and hopefully the noise will stop, need insulators on back of pads.
 

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Discussion Starter #13
I always thought that most factory rotors could be machined at least once and still have enough thickness, unless pads were severely worn and started eating the rotor or it was too badly warped. You don't need new rotors at every brake job.
 

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I always thought that most factory rotors could be machined at least once and still have enough thickness, unless pads were severely worn and started eating the rotor or it was too badly warped. You don't need new rotors at every brake job.
First, rotors don't warp, it's just uneven pad buildup, and as far as cutting let's look at the numbers. Thickness new 1.103", discard 1.039" that means only 0.064", or 0.032" each side can be removed from new before the rotor is not to be used. A credit card is @ 0.30" thick, so one can see that only the thickness of a credit card can be used, then throw away as most used rotors when cut, will always be under the factory minimum. Rotors will wear significantly and may be under the factory minimum at time of a brake pad change, so they become a throw away item. One might notice the large lip around the edge of the rotor where the pad doesn't make contact.
That is the original thickness and the braking surface is most likly more an a credit card from that lip.

On the other hand, some, let's say some expensive rotors will live through multiple pad changes, but one needs to be aware of the tolerance before making a decision on turning the rotor. If under cut, it causes additional heat and the possibility of other problems. The minimum thickness will be on the rotor somewhere, but may be hard to read after years of use, so it's wise to check, but with the cost of replacement rotors one is better served to just do a replacement.

I know long winded, but last year was at a Kia dealership getting the 2.0T update, and a woman was paying the bill for a brake job and one of the items was for the cutting of all 4 rotors. I couldn't stop myself, so mentioned that to the service manger, away from the woman, that after cutting the rotors they will be under the minimum spec, and his reply, "yeah, they will be under the minimum, but Kia approves cutting the rotors". Figures, nobody cares, just more money in their pocket.

Time to take the Goldendoodle out.
 

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I always thought that most factory rotors could be machined at least once and still have enough thickness, unless pads were severely worn and started eating the rotor or it was too badly warped. You don't need new rotors at every brake job.
With the cost of labor being so high nowadays, the incremental cost increase of new rotors is not very high as compared to paying for the labor to have them turned. At least aftermarket rotors, I don't know what the genuine Hyundai rotors cost. And I've had good performance with aftermarket rotors from reputable brands.

Plus the time involved in taking them in and waiting for the job to be done - once they're off the car you have to borrow your significant other's car to take them to the shop. I lived somewhere a few years back where the parts store was within walking distance, so I walked them over there one time, but otherwise, you're going to have to borrow a car, bike, something.

I just buy new ones every time now.

Although I have to say that I miss being within walking distance of the parts store! That's great when you need something and the car is already apart. But anyway.
 

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With the cost of labor being so high nowadays, the incremental cost increase of new rotors is not very high as compared to paying for the labor to have them turned. At least aftermarket rotors, I don't know what the genuine Hyundai rotors cost. And I've had good performance with aftermarket rotors from reputable brands.

Plus the time involved in taking them in and waiting for the job to be done - once they're off the car you have to borrow your significant other's car to take them to the shop. I lived somewhere a few years back where the parts store was within walking distance, so I walked them over there one time, but otherwise, you're going to have to borrow a car, bike, something.
Not to mention trusting the rotor lathe to be serviced properly and in spec at "Joe Bob's muffler and tire". Not that I'm an environmentalist but I don't have heartburn throwing old rotors in the metal recycling bin and just using new ones at every brake job.
 

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The main thing about a new rotors is they are ground to a finer finish much better than any lathe can do. Labor cost is a big factor when deciding which way to go.
 

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When a rotor is sufficiently worn, and the pads are very low.... Sometimes that "lip" on the outer rim of the rotor surface where the pads have not worn the rotor, contact is made there and a grinding "growling" noise is heard. SOME pads are wider at their base where adhered to the metal backer plate.

Measure the rotor thickness, check the pads inner and outer. New rotors about the same price as cutting the old ones (if you DIY).
 
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