Brake rotor wear - 986 Forum - The Community for Porsche Boxster & Cayman Owners

Frodo · 08-06-2012, 09:08 AM

Getting ready to do my first brake pad replacement. PO must have done the fronts before I bought the car, since I have more pad material in front than in the rears, so at the moment I'm just doing rear pads.

At one point maybe a year ago I took the car into a dealership so we could put it on the lift and he (& I) could take a good look underneath. (I had been doing most all of my own regular maintenance and I figured I'd have someone more knowledgeable than I at least inspect things for a change.) He had several suggestions that I won't go into here, but at one point I asked him about the brake rotors.

I asked because, obviously, the pads wear into the rotor and in doing so leave a narrow "lip" of material at the outermost edge of the rotor. He said I shouldn't have the rotors turned, but I could take it to a machine shop or brake place and have them just take off the lip. In the alternative, he said I could bevel the new pads a little for fitment purposes.

Now that I'm about to do the pads, looking back on what he said I can't really understand why he said that. Don't the new pads just fit into the worn area of the rotors? Or are they shaped slightly different depending on who made them? (I've had no complaints about braking---I'm inclined to just use the same brand of pads.)

BTW, the lip is about 0.5 mm each, inside and outside. The rotors are at about 23 mm, and the spec service limit (Bentley manual) is 18.6 mm, so they should be fine without replacing I would think. The car's got just over 65K miles on it.

mountainman · 08-06-2012, 09:22 AM

I generally get 50 to 60K before doing a brake job so I generally anticipate the change and watch for deals on the pads, rotors, sensors, etc and put everything on new. However If the rotor is not worn down too far I see no reason why new pads will not seat to the existing rotors. Granted each pad and rotor will wear differently and there may be some what less performance than with everything new, but not a tremendous amount
I generally spend less than $500 to do iit all the way around with the oem or better components, whereas the dealer will want around 2K. I don't mind spending $500 on brakes every 50,000 miles.

thstone · 08-06-2012, 11:46 AM

For the best performance, it is best to turn the entire rotor. This will remove the lip and give the new pads a perfectly flat and appropriately roughened surface to bed into. I don't see any advantage in having a machine shop remove just the lip (and not turn the entire face of the rotor) because most of the cost in turning a rotor is generally in the setup.

stephen wilson · 08-06-2012, 11:56 AM

Agreed, if the rotor is above the minimum thickness, and isn't badly grooved, throw the new pads on and be done with it. They will seat themselves just fine. If you turn the whole rotor face, you will generally end up below the min. thickness.

mountainman · 08-06-2012, 12:46 PM

bear in mind, some of these cast iron rotors are not turnable.

Dave928 · 08-06-2012, 12:50 PM

the lip is .5mm? that's nothing. put the pads on and drive it.

btw: this is too much rotor wear:

stephen wilson · 08-06-2012, 01:23 PM

That rotor's fine, there's a whole 'nother side to it! Besides, the ridges give extra grip, and help wipe the pads.

Overdrive · 08-06-2012, 01:29 PM

Quote:

Originally Posted by Dave928

the lip is .5mm? that's nothing. put the pads on and drive it.

btw: this is too much rotor wear:

Dave, WTF?! Where did that come from? That's just nuts...

It's my understanding that one is not supposed to turn these rotors and simply replace them every 3rd set of brake pads, provided you replace your pads when required so you don't do any additional damage to the rotors. That groove that develops on the edge of the rotor would be your gauge for how close your rotors are to requiring replacement. If you're still within the threshold for replacement, then you should be able to just put the new pads on and go.

As mountainman pointed out, $500 isn't really that bad at all for an infrequent expense, and you'll have fresh hardware all the way around.

Just out of curiosity, have you checked the difference in the size of the lip on the rotors in front vs. the rears you're looking to replace?

san rensho · 08-06-2012, 04:40 PM

As long as there is no vibration when you apply the brakes at high speed and the rotors are above the minimum thickness, just use the same rotors, even if there are slight visible grooves in them. The new pads will conform to the grooves and the lip.

bar10dah · 08-06-2012, 04:51 PM

Those are the new vertically slotted rotors. They're the latest "in" thing for ricers. Almost as popular as the cross drilled brake lines.

Dave928 · 08-07-2012, 09:07 PM

when i was a VW Tech one of the other techs bought a truck that was a trade-in. he found that when he went through the brakes. opposite rotor was the same.

opus69 · 08-08-2012, 03:12 AM

Two things I never try scrimp on: tires and brakes. I don't ever remember having any rotors turned on any vehicle I have owned and I have done a lot of brake jobs over the years. Recently I did a brake job on my 2002S w 43,000 mi. The pads looked original and were worn almost to the sensor. Rotors had .5+ mm lip so I just replaced them. That extra foot of stopping distance may be important in a critical situation.

jcb986 · 08-08-2012, 06:48 AM

Seems to me that kind of rotor will eat up pads. Looks like a cheese grader.

thstone · 08-08-2012, 07:12 AM

I always replace my rotors with every pad change. Yes, might be excessive and more expensive and this is definitely not required but I have also never had a brake problem and want to keep it that way.

Jager · 08-08-2012, 04:53 PM

Quote:

Originally Posted by thstone

I always replace my rotors with every pad change. Yes, might be excessive and more expensive and this is definitely not required but I have also never had a brake problem and want to keep it that way.

Ditto, I do the same.