What Percent of brake life is 3mm?

Can anyone tell me the approximate brake life remaining when a brake pad has 3mm remaining? What is the usual new thickness and does the pad actually have 3mm left when that is the measurement, or does some pad thickness need to be remaining for the pad to still operate properly? In other words, can it still work at 1mm? Thx

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Tester

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Most new brake pads are 12mm and 3mm is replacement time . As to how far or how long is dependent on the driving ( city with many stops or highway with very few stops ) .

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Friction material thickness varies quite a bit between various vehicles and even optional brakes on performance cars. For that reason, you can’t say 3 mm is 50% worn or 80% worn. The pad thickness on my Mustang is different front to rear as it is my Audi. My truck is the same.

Per Testor’s picture, that is for people who ignore their car’s maintenance…which is what service centers would assume every customer is for legal reasons. The wear tabs that screetch when the pads need replacing are spaced about 2 mm out. Same for wired wear indicators.

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1.Jack up the front of the vehicle and support it with safety stands.

2.Remove the wheel and tire. (See WHEEL AND TIRE REMOVAL/INSTALLATION.)

3.Verify the remaining thickness of the pads.

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Minimum front disc pad thickness

2.0 mm {0.079 in}

• Replace the pads as a set (right and left wheels) if either one is at or less than the minimum thickness.(See FRONT BRAKE DISC REMOVAL/INSTALLATION [WITH SINGLE PISTON FLOATING CALIPER].) (See FRONT BRAKE DISC REMOVAL/INSTALLATION [WITH 2-PISTON FLOATING CALIPER].)

The above is a cut and paste from the factory service manual for a 2018 CX-5.

New brakes will be 10-12mm, most manufacturers say 2mm is minimum lining thickness. Replacing brakes at 5mm is wasteful, like replacing tires when there is still 5/32" of tread remaining.

You can’t express brake pad life in percentage because it largely depends on driving habits and that can change on a moments notice. So if I tell you that a new brake pad is 10mm, minimum is 2mm, and yours are at 3mm, you can decide to replace them now or wait. Yes, a brake pad will work at 1mm, but you’re one panic stop or downhill grade away from grinding into the rotor. I would say you’re close enough.

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I wouldn’t panic at 3mm, but I’d start making plans. There are a lot of factors here. How many miles on the current pads, what was the original thickness. That can give you an idea of how many miles are left.

I’ll use my car as an example. The dealer told me that my rear pads were at 3mm, he lied but thats not the point. I don’t know why the mechanic would pull my rear wheels when the car was in for a takata air bag recall. But anyways, the car had about 100k on it. The OEM thickness is 16mm.

If the pads had really been at 3mm, that would mean I had worn 13mm off in 100k miles. That would be about 7700 miles per mm of wear. You can go to 1mm but you risk damaging your rotors. Any way, I figured I needed to replace them sometime in the next 10k miles.

It was spring and the weather was nice so I decided to go ahead and replace them. I ordered new pads from RockAuto and one fine day when it was particularly nice and I had nothing else to do, I replaced them. The most worn down rear pad still had 6mm left.

BTW, he also told me that I needed a new cabin filter. BS, I had just put a new one in. Everyone else in the waiting room was also told their rear brakes were at 3mm and they needed a new cabin filter.

Edit: I was doing an inspection on my daughters car and I noticed one of her rear pads was down to 3mm. For her I ordered pads and did them the next weekend. She is notoriously hard on brakes and I calculated that she had about six more weeks of life in them before they got too close for comfort.

Every case is different but I hope you have enough information to make good decision for yourself.

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3mm is about 50% worn, if this is the wear limit:

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Massage-o-matic brakes? … lol .

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If mine were at 3mm I’d replace them, that’s a bit over 1/10”. A concern is how evenly they’re wearing. One area could be at 3mm, some other area at 2mm or 1mm. If you want to cut it close, you’ll need to look at every pad.

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No. Depends how the person drives.

Original thickness depends on manufacture, there is no standard “new thickness”. If it is measured at 3mm. then it is 3mm. Yes there needs to be some pad thickness remaining. Metal to metal is not effective, and will cause damage.

Yes, but not for long.
Coming from you I really hope these questions are rhetorical or just meant to get a discussion going.

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I also thought it strange for John Goreham to start this thread . Seems like he would post research on the subject . I think the people who are now in charge are trying to increase participation in the Forum . Who ever is the current Web Lackey has also started some threads that did not really have much response .

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Happy Thanksgiving Volvo.

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Thanks, everyone. Very helpful. Sometimes I think this is the best place to find out an answer with details, which is why I asked here. To Volvo’s point, I don’t usually create a post as Web Lackey here. Have not done so in a long time.

Dealer quote for front brakes (Pads and rotors plus usual labor only) $690, but loaner car offered. The local shop estimate is “About $400.” Going to try the local shop and do the drop off and pick up routine. Need to find a new trusted mechanic anyway, and this is a great test.
Cheers and happy holidays,

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Look, if a semi-metallic brake pad is superior to an organic pad, then a full-metallic brake pad should be even better, right? :laughing:

Just out of curiosity, what’s your methodology for choosing an auto shop? Is price a major concern?

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Yeah I guess I had it all wrong. More is always better :rofl: :joy:

It appears from some responses that the wear rate on a pad is thought to be linear over its lifespan. My suspicions are it is not.

Empirically, I have far fewer rotor issues if I am more proactive at pad replacement than if I let them get very thin before changing them out.

I believe the pads transfer more heat and faster as they wear. Most braking is very intermittent. On a thick new pad, the material has a thermal gradient across it, allowing it to absorb the heat being produced. As the material diminishes, this capacity also does and everything gets hotter faster. The binders in the pad material are subjected to ever higher thermal loads and so break down faster as the pad wears. There’s a whole scientific discussion out there regarding wear shed, shearing, outgassing effects on wear and so on with the pad design folks if you care to read it. I won’t go into that but just summarize my thoughts above.

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I would think that if the pad material has low thermal conductivity it acts as an insulator, so the surface of a thick pad will get hotter than a thin pad.
OTOH, once a pad gets thin the remaining material has been subjected to long term high temps and outgassing, which might reduce its cohesion and resistance to wear.
Thus, heat degradation might cause thin pads to wear away faster.

Heat capacity is a big part of the puzzle with intermittent use.

Make sure you are getting an apples to apples quote. You want to get new hardware with the pads. If this is the first brake job done on this vehicle since new, I would recommend NOT changing the rotors. Almost all factory rotors are good for two pad sets and still have some meat left over. They also seem to be less prone to warping than many after market rotors.

Also make sure you are getting at least OEM quality pads. Find out exactly what pads are going to be used, brand and model.

Lastly, get the brake fluid flushed with the pad change. If you haven’t been following the recommended PM schedule for Brake fluid exchange in the owners manual, then you should at least flush/exchange the brake fluid with each pad change.

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You want to install new rotors with the new brake pads.

In order for the new brake pads to bed properly, the rotors require the proper surface to do so.

The old used rotors don’t have this proper surface to accomplish this.

And you could end up with brake noise.

Tester

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