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Old 11-20-2008, 03:24 PM   #1
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Brake Wear Specs

I have a 99 Boxster with an intermittent beak wear dash light. I have been unable to find the minimum operating specs for rotors and pads. After inspection, I found a 1mm lip around the edge of my front rotors and about half that on the rear. At what point do the rotors need to be replaced? Previous owner replaced front pads and rotors at 48k miles (currently at 96k) with OEM parts at an Authorized Dealer.

I am new at vehicle DIY but, after reading the other posts, I think I will take a shot at replacing the pads and rotors, if necessary.


Any help is appreciated!
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Old 11-20-2008, 06:40 PM   #2
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Because the rotors are thick enough you could probably get away with just pads. I do not know the wear specs either, I'm sure someone here does. I have heard the best bet is two sets of pads per rotor.

I am about to do the same thing. I deemed the rotors were good enough so i am flushing the fluid and changing all the pads.

Get a motive power bleeder. You can do it without but why?

just my .02

-Greg
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Old 11-20-2008, 09:29 PM   #3
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There are wear limits. These are:

New:

Front: 24mm (0.94 in.)

Rear: 20mm (0.79 in.)

Wear Limit:

Front: 22.6mm (0.89 in.)

Rear: 18.6mm (0.73 in.)

Machining Limit: ('after' machining)

Front: 22.0mm (0.87 in.)

Rear: 18.0mm (0.71 in.)

Plus, there's a Peak-to-valley surface roughness measure of the brake disc after machining, which is: Max. 0.006 mm.

Finally, the Lateral Runout of the brake disc, which is: Max. 0.03 mm.

You need to use a mic or caliper on several spots around the rotor and avg. your readings to determine replacement or not, and a dial gauge to measure the lateral runout.

The rule-of-thumb is that you get two sets of pads out of each set of rotors (street pads - if more agressive street/track pads are used, you need to adjust for this). Again, pads usually last 30k-35k mi. You can use the car's mileage to roughly determine if rotors are needed. I would say that if you have 55k mi.+, you should probably be looking at rotors too. Again, you need to take into account the driving style too, these 'rules' are for 'normal' use. Total freeway miles and you can extend this a bit. Total in-town stop & go, or track, ax, or de days and you should use reduced limits.
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Old 11-21-2008, 11:37 AM   #4
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pardon the hijack, but in the process of putting in a rear wheel bearing, on my '01 S. I measured my rear disc and it was 22+ mm. Do 'S' and base use the same discs? The bentley makes no such distinction. Did a previous owner put front discs on my rears? Weird.
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Old 11-21-2008, 12:48 PM   #5
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Quote:
Originally Posted by brp987
pardon the hijack, but in the process of putting in a rear wheel bearing, on my '01 S. I measured my rear disc and it was 22+ mm. Do 'S' and base use the same discs? The bentley makes no such distinction. Did a previous owner put front discs on my rears? Weird.
The Base and 'S' do not use the same discs. The discs on the 'S' are 318mm (f)/299mm (r) in diameter vs 298mm(f)/292mm(r) for the base.

Also, new the 'S' rotors are 28.0mm(f)/24.0mm(r) with wear limits of 26.0mm(f) and 22.0mm(r).
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