when do you need new rotors...?

My brake light has gone on and I was thinking of just replacing the pads... is it true that rotors need to be replaced as well? somebody told me that aftera while the rotors have grooves in them that were made by the pads and fresh pads will cause considerable steering wheel shake if the rotors aren't replaced as well... the car has 43,000 miles on it and rotors are stock... any opinions?

When I got my brakes replaced around the 50K mile mark on my 996, I was told that the rotors needed replacement as well as pads, and that Porsche recommends this. I may have just been a sucker, but my maintenance on my lease was subsidised so it didn't end up costing me all that much more just to do it.

Its not the grooves that will shake the car, but that over time the heat will make the rotar not staight and that will cause the shudder. Generally speaking if the car does not shake now it won't with new pads. However if the rotars do have considerable groove the braking efficency is reducesd and you can get brake squeel noise. The only true way to know if the rotars are done is to have the thickness measured and see if they can be resurfaced. Given that you have so many miles its probably time or close to it to replace them. Only a machine shop or brake shop can tell you if you do. The dealer will tell you to replace them because they will want to up sell you. Its hard to find a honest opinon out there.

Depends how you have driven those 43K miles. But basically it comes down to rotor width and condition of rotors. The crossdrilled rotors can not be turned if I remember correctly, so if they are warped or gouged, you will have to replace them. If they are true, and within size spec, just replace the pads. You will only have steering wheel shake if the rotors are warped. The number one cause of warped rotors is improperly torque rotors, by the way. So make sure they are properly torqued by the people that do work on your cars (which is rare for them to do it right). If your rotors have groves, you can still use them. The pad material is pretty soft and it will conform to the groves quickly. In my less rich days, you should have seen the groved rotors that I reused with no problem!

How do you torque rotors? They are held in place by two very small screws until you put the wheels on. Do you mean torquing the wheel bolts? Rotors are cheap so you might want to replace them just to be safe. As I recall they are around $140 each and very easy to put on. There should be almost no labor if they are also changing the pads. Maybe 1/2 hour at most. You'll also need new caliper bolts. It is unlikely that your rotors are warped. They can take a massive amount of heat. (to start a debate, many experts don't think rotors ever actually warp. The shutter is caused by deposits) They may be too thin or they may be cracking. Look for little cracks between the holes. If they are close to connecting or if any cracks are reaching the edge then you should replace them. Just my ideas. They could be wrong. Jim

I have not yet replaced my stock pads (48,000 miles), but I will probably throw on a new stock rotors when I do. They are cheap enough and easy to do. However, replacing them is not necessary as long as they are true, thickness within specs and minimal cracks around the holes.

How much to OEM brake pads and rotors cost, if you decide to replace both? What would be the labor costs?

I am just going through the same decision process.

Rasta: Car & Driver suggest in their long term test, that the C4S brakes will last the life of the car or 100k miles.

I have had to replace both fornt and rear rotors on my 996 C2 due to wear below the minimum thickness. Both were below minimums at nearly the same mileage. I didn't make it to 100k as stated in previous posts...only about 95k miles and they were below minimums. No track, but a couple of autox. YMMV

just a reminder that the C4S comes with the much larger turbo brakes; so not really comparable.

What is said above is mostly great advise. However, I didn't see anyone mentioning small fractures that may appear near the holes (although I could have missed it). These cracks need to be watched carefully. If they become too stressed, the rotor could fail. Check them carefully and replace when needed...as has been said, they're not terribly expensive.

when do you need new rotors...? If you take your car to Prestige Porsche then it's every time you need an oil change.

AFAIK, there are three main factors to consider: 1. width of rotor -- Porsche publishes specs on when rotors must be replaced. I don't have it in front of me but someone should be able to chime in. 2. warped rotor -- It is unlikely that your rotor will be warped if your width is in spec, but I guess it could happen 3. cracked rotor -- You should replace your rotor if the cracks on your rotor either (a) join two holes [or are more than 2/3 of the way to joining the holes] or (b) go from one of the holes to the edge of the rotor. The rotors are about $100 each. Since you do NOT want to replace your pads and your rotors at the same time, I would not let a dealer do it. Buy them from suncoast or somewhere else and then replace them after your new pads are worn in.

Hey TD... thx for the info... I will inspect them tomorrow... I don't remember seeing any cracks as you describe them... the only thing is (and this may be normal) if you slide your finger from the center of the rotor to the top... there is a bit of a lip right at the edge of the rotor... one of the tech guys (Porsche) told me if I didn't replace my rotors and just did pads... the steering wheel would shake violently... sell tactic? it's funny... about 6,000 miles ago when I had the car in for an oil change the dealer wanted to replace pads.... you know the standard "lets' replace everything"... but they never commented on the rotors... now at 44K miles the rotors must be replaced... hmmm just 6K ago it wasn't an issue... I don't know...

The lip at the edge is normal and is a result of disc wear where the pads touch. And, yes, most dealers will try to sell you all sorts of services when they are not necessary. Like RMS replacement when there is no oil leak from the seal??????? Always verify any problems a dealer says exists.

yep. that's the sort of tactic that forces you to no longer trust that person. i just did all pad replacement, and i can tell you there is absolutely no shake whatsoever. and there never has been when i do pad only replacement on many of my cars. i change a lot of pads because i always replace with low dust pads like EBC, ceramics, or in the 911 case, Mintex.

how do the mintex compare to OEM... are they as grippy? I don't mind the dust... I don't want brake squeal and at least OEM performance; are they cheaper than OEM pads?

Where to you buy the tool to measure the caliper thickness? Thx

Mintex seem to have the same brake feel as stock. I don't know how much OEM's cost, but for all 4 wheels, Mintex was less than $100. There's no brake squeal. I wouldn't go for that either. Calipers can be bought at any fine tool parts store. You can easily search the web for companies that will ship them to you.

What an absolute load of crap! I am very thankful that my service techs are track junkies and honest. You do NOT want to replace pads and rotors at the same time. If you have your sensors still in your pads, you don't need to replace them until your warning light comes on. I removed my sensors (actually, just zip tied them out of the way), so I inspect mine visually every weekend. You need to replace your pads whenever the pad thickness is equal to or less than the thickness of the backing plate. Easy to check without even removing the wheel. The only thing that should be shaking violently is the tech's neck after he tries to tell you that you must replace your rotors when you replace your pads or vice versa. As 1999Porsche911 pointed out, the ridge is not a problem per se. The thickness of the narrowest portion of the rotor is what counts. Also, "grooves" on the rotor are not a problem either. Mine are well grooved but my brakes are outstanding.

You can spend $$$$$$$$$ by buying a nice one from snap on tools, or you can do what I did and buy one from Home Depot. Just make sure you get one with a metric measurement scale because the tech specs from Porsche are, of course, in metric. Also, when measuring your rotor thickness, be careful not to bend your dust shield ( or accidentally include it in your measurement). If you do, you might cause it to scrape on the rotor when you are driving. Ask me how I know . . .

Thx TD. What is the measurement point / metric for when they are too thin?

The minimum thickness for the fronts is 1.025 inches and the rears are .875 inches. Use a caliper to measure accurately.

Much appreciated. Also, my caliper is in inches so this REALLY helps! Thx!

TD - why do you say to never replace the rotors and pads at the same time? This is what the dealer normally does for service. I have a new set of rotors and pads I am getting ready to install and wonder if I should do the rotors first now and then the pads later per your advice? thx John

No, it should NOT be what the dealer normally does unless they are trying to upsell. If you install rotor and pads at the same time, it becomes harder for BOTH to break-in. Think pad glazing and perhaps smear (ask Jeeva what that is like). It is far better to install new pads, get them broken-in on the old rotors, which should not take very long, and then install your new rotors.

Thanks TD -- so I need to do it the opposite of what I was planning. New pads first and then rotors. thx John

No problem. Keep in mind that if your old pads still have plenty of life, you can install your rotors first, break them in until your old pads really need to be replaced, and then put in your new pads. I think it probably takes just a little longer to break-in your rotors, so if it were close, I personally would change the pads first, then the rotors.

D'oh! Thanks for pointing out the obvious fact that you can convert. Sadly, I bought a metric caliper without even thinking of converting. Nothing like a brain fart that lingers a little too long

Where do you take your car for service TD?

I take the 996 to Porsche of Arlington for all service except for suspension and alignment work, which I have done at Autobahn in Fairfax. I used to take my former 986S to HBL of Tysons where I bought it. I take my 944 to RPM in Newington. We are lucky around the DC area because there are many good shops.

I don't know how some of you guys are driving to get your pads to last to 45K or 50K miles , but mine were shot at just under 30K and I didn't track the car (996 C4). I just swapped out the pads, visually inspected the rotors, and was on my way. No problems at all!

Just had mine replaced all round (Discs (as we call them) and pads). - Cost � 1100.00 at Porsche dealer. I'm staggered by the increase in braking performance now. Much more even and much less pedal travel. My discs were absoluetly knackered and worn down below the minimum thickness at 29,000 miles. However this is partly the fault of the supplying dealer who at one year old scimmed the discs to remove corrosion. Adrian

LOL. i agree with you, but the BMW dealers near you wouldn't think of replacing pads without also changing the rotors. It's a text book case of upselling.

True most dealers are interested in upselling these days since cars tosay require less maintanence. However I disagree with TD remarks. Yes rotars and pads that are new may take a little longer to break in, but its not that much longer. I feel you are giving bad info, the fact is that if the rotars need to be replaced then do the pads too, because an uneven pad can cuase pressure points only on certain spot of the rotor thus wearing them uneven. In general a rotor that needs to be replaced has grooves in them and may even be warped so the pad will have defects that I would not want to scrape them on a new rotor. In general you can break in most pads with 100 miles of normal daily driving, unless your daily trip is 100 miles of pure highway.

If someone has let their rotors AND pads both wear to the point that they cannot break-in a set of pads (which takes only a couple of hours (or even less) as a search on this forum will explain) before replacing the rotors, then they really need to learn about preventative maintenance or let their dealers have it for letting their machinery get into such bad shape. I am not giving bad info. I am not saying that you should not replace both. I am saying that it is far better to replace one then the other, and both can replaced in the same day. I completely disagree with your comment about the grooves in the rotor will cause the pads to develop "defects." Pad will conform to the rotor. Just as they conformed to the grooves, they will reconform to the new rotor. The pads are not so stiff that they will carve grooves into the new rotors. I think you may have misunderstood what I am advising, or perhaps we just disagree.

Well you can tell this is not the OT forum. I commend both jetskied and TD. They disagreed but there was no flaming nor name calling.

No need for namecalling! We all share the same passion and all have the same goal: to help each other learn a little more about our P-cars! Besides, I would hope that Jetskied would want to buy me a beer (or a wine) if I ever make it to his neck of the woods, even if he does think my info on rotors is bad (even though it's not ).

I chalk that up to maturity. Although I'm certain that there are some posters on this Board that are in their teens, my guess is that most are much older and hence you won't find as much flaming here as you find on other Boards.

When I was reading it, i thought, oh no TD is not going to take this well.Well done TD, i was sure a rip n' tear was comin'

Nice job Todd! Once again, great explanation.