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Minimum pad thickness


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Just got through replacing the brake pads on my wifes '07 Buick with four wheel disc brakes. After pulling the calipers on both ends I found both sets needed replacing.


So I glanced at the pads through the wheels on my '03 Baja and they look like they are going to need replacing soon. Best I can tell. The car only has 65K miles on it and I'm not hard on brakes and the car is a 5 speed so I tend to gear the car down on hills rather than riding the brakes like most people do especially with automatics.


So I can't understand why the car would need pads this early. Unless that's just normal wear on a Subaru.


I'm going to pull the wheels off and see if I can measure the thickness with a slide ruler without pulling the calipers.


Any idea what the minimum thickness of the brake media is which would merit replacing the pads?


Since this is MY car and not my wife's car and I have plenty others to drive if the brakes start squeeling, I thought about just waiting until the squeelers got down to the rotors before replacing the pads.


Also when I hit the brakes I can feel some vibration in the steering wheel. The rotors are smooth and ordinarily I would not have the rotors turned but I'm wondering if the vibration is from warpage. Either from a tire store using an air impact wrench to put the wheels back on or they got hot and lost their temper.


I'm concerned if I have them turned, if they have lost their temper, the vibration will come right back.


Just curious.

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65,000 miles on the car - is that the original brakes? That's really good actually to get 65,000 miles on front pads. and you're not to the wear indicators yet so you have more mileage to go.


I would wait until the wear indicators start sounding off. they give you plenty of warning and you can drive them for awhile after, giving you plenty of time to arrange parts/repair. And who knows - you might get another year or two out of them.


As for the vibration, you can google it but rotors don't technically "warp". I think it's more like material build up and driving style and conditions are most likely to make it happen again. There are some excellent technical reads about it. So turning is a fine solution.


Sometimes you can tell which side it is...turn the wheel by hand and you'll feel it hit a high spot - that's the warped one. If you can't tell then install a new rotor on one side and then:

1. if it goes away you're done

2. if it doesn't go away then install the rotor you removed to install the new one on the other side


Or just replace them both or have them both turned, lots of options.

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Also make sure to check the thickness of the rotors. Discard spec for those is .866" and usually you can turn them once before they need to be replaced unless its gone metal to metal.


Brake pads I usually replace at 2mm thickness but recommend doing them at 4mm. I use Akebono brand pads at work as those are pretty much a standard OE replacement pad. Remember, the cheaper the pads, the worse the braking performance and they can also make noise.

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The squeal plates hit the disc around 2-3mm of material, the absolute minimum.


For track application, "we" like to replace when the material has worn down to the same thickness as the backing plate: 4-5mm.


In both cases, it's a question of heat. You need the material to absorb the heat from the disc/pad interface. The last few millimeters should never see any real braking action, but simply act as a heat sink.

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Yes 65K miles, original brakes. I bought the car new about two weeks before Christmas in 2002. It's been one of the best cars I've ever owned. So far the only two issues have been a bad O2 sensor ($200 expensive yet took me 30 minutes), and a blown inner CV joint boot ($20 but took me 6 hours to fix it).


I printed this conversation off and will inspect the pads when I get a chance and take some measurements.


And yes it's probably not a bad idea to change them before winter. My Subaru get's driven mostly during the winter months. Living in Tennessee, it can be 70 degrees in January one day and 6" of snow the next.


I tend to drive my Mustang GT in the summer as well as some of my other collector cars.


And I'm a blue collar worker at a chemical plant so I can't just bail out like management does when the weatherman is calling for a big snowstorm like back in 2009.


It started snowing around 3 pm that day and I didn't get off until 6:30. Management bailed out and went home while all the worker bees had to stay behind.


My Subaru got me home without incident but it took forever having to wait on people trying to make it up hills. Or having to take detours because of all the abandoned cars parked in the road (on hills).


I hate to have a chip on my shoulder but I finally got so pissed off at these people I just started driving around them while they were spinning out.


I mean, I love my Mustang and all my other rear wheel drive cars but when the conditions are right for a snowstorm, those cars stay in the garage.


Here are some shots I took the day after. Notice the abandoned Mustang on the interstate (photo 19 of 43).



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My boss had three vettes. He was a pompus twit. He couldnt even get out of the office driveway one day when we got a surprise snow storm, and all the mustangs and other cars with summer tires just spun and spun and spun, so it is always fun to make fun of them.

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I've changed the rotors/pads in my Legacy about 3 times since 70K... Mostly due to emergency stopping in LI due to people who can't judge space/speed from another car.




Like they all said, just replace the parts, even go one better and flush the fluid. I'm sure it will help wonders once I do it on both of my Subaru's.

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  • 4 months later...

Sorry for the thread mining but I finally got around to checking the pad thickness on my 2003 Baja.


The other day the brakes would squeel slightly when applied so I was afraid the squeelers might be getting near the rotors.


So I pulled the front and rear calipers on the passenger side. ASSuming because the car stops straight I am going to say there was no need in checking the driver's side. And because I've done tons of brake jobs in the past pads usually wear out the same on both sides.


Using one of those slide calipers that has the pocket clip on it:


I measured the actual thickness from the backing plate to the media. Not from the groove cut into the center of the media.


The front pad thickness was 5.5mm and the rears was 4mm.


The thickness of the new pads I got from Advance Auto were fronts: 10 mm and 8 mm rears.


Does that sound right? Or is my cheap slight ruler marked incorrectly?


So that leads me to believe after 70,000 miles the pads have only worn down half and if my driving habits don't change I shouldn't need to install new pads until 140,000 miles.


Is this a good assumption?


I use my engine as a brake instead of riding my brakes when going down steep hills and even on flat land tend to gear down to 3rd then to 2nd and then hit my brakes at around 20 mph before coming to a stop.

Edited by jseabolt
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I have no idea if pad material can break down with time so, I'd say your calculations are as good an indicator as anything else would be. I suppose it might still be a good idea to tear down and lube stuff as I'm sure exposure/time/corrosion etc. can still affect the slide pins and other moving parts.


In the US, there can be a slight asymmetry to pad wear favoring the pass side. this is due to parking at the curb where gravel, leaves and other debris may allow a little sliding that the DS doesn't experience. This is most extreme on Postal Vehicles but, the DS is probably the best 'tattle-tale' for general pad wear. And, suppose a caliper is sticking at one of the other 2 corners?

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  • 1 month later...

I can tell you from selling auto parts (we surfaced rotors and flywheels too). Rotors do warp do too rapid heat changes. Most can be machined one time before replaceing them. As for pad thickness a rule of thumb we always went by was when the material on the pad gets down to the same thickness as the metal its mounted too its time to change them. You want try and avoid getting to the wear squeakers they can groov your rotor

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