Pads AND rotors?
03-10-2018, 09:00 PM
#1
Rennlist Member
Thread Starter
Pads AND rotors?
I am into my second year of ownership of my C4S. When I bought the car I replaced pads and rotors all around. I put on pads for 80/20 Street/track use. I can’t remember the pads but I just had them replaced and was told I needed new rotors as well. Is this normal? The tech said that’s what they typically do. I had a 964 prior to this beauty and have to say I would get 3 pads/rotors replacement. Anyways, thought I would ask the community here. Thanks
03-10-2018, 11:01 PM
#2
Rennlist Member
Unless the pads you were using were too agressive (metal?), the rotors shouldn't need to be replaced that soon.
03-11-2018, 08:01 AM
#4
Drifting
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Location: Ephrata, PA, USA now. Originally from the UK
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If the rotors need to be changed you should be able to feel a lip on them. It's an easy enough job if you have an impact driver in your tool kit. Go for it.
03-11-2018, 11:36 AM
#6
Instructor
IMHO the best method is to measure the thickness of your rotors using a micrometer (Harbor Freight makes an economical 3-tool set which is plenty accurate enough for this purpose). Provided the rotors are above minimum thickness and show no significant cracks linking up between ventilation holes, you're perfectly fine reusing them. The minimum thickness is cast or stamped into the rotor (factory ones, at any rate) or you can find this info in the service manual.
Brake rotors are a wear item and WILL develop a "lip" in use. It's how big the lip is--or, conversely, the thickness of the rotor in contact with the brake pads--that really matters.
Good luck.
Brake rotors are a wear item and WILL develop a "lip" in use. It's how big the lip is--or, conversely, the thickness of the rotor in contact with the brake pads--that really matters.
Good luck.
03-11-2018, 10:22 PM
#7
IMHO the best method is to measure the thickness of your rotors using a micrometer (Harbor Freight makes an economical 3-tool set which is plenty accurate enough for this purpose). Provided the rotors are above minimum thickness and show no significant cracks linking up between ventilation holes, you're perfectly fine reusing them. The minimum thickness is cast or stamped into the rotor (factory ones, at any rate) or you can find this info in the service manual.
Brake rotors are a wear item and WILL develop a "lip" in use. It's how big the lip is--or, conversely, the thickness of the rotor in contact with the brake pads--that really matters.
Good luck.
Brake rotors are a wear item and WILL develop a "lip" in use. It's how big the lip is--or, conversely, the thickness of the rotor in contact with the brake pads--that really matters.
Good luck.
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03-13-2018, 08:46 AM
#8
Rennlist Member
I'd say change the pads, leave the rotors and find a new shop 
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Bash Hat (12-27-2019)
03-13-2018, 01:53 PM
#9
Race Car
With the amount of track time you have planned, they'll crack up pretty fast and need replacing long before they wear down. So unless they are already close to wear limits, I'd say reuse them. Also, every time you remove & reinstall the calipers to change the rotor you are getting closer to the inevitability of stripping the threads on the upright.
For the caliper bolts, use a little PB blaster and always start them by hand to prevent this. If you can’t get them started by hand, remove the brake pads and try again. After having two wheel carriers cross thread on me I’ve learned to be extra careful. Haven’t had a single problem since doing the above. The bolt for the front brake line bracket is even worse. I swap it out for an m6 stud on any car I plan on keeping.
03-13-2018, 11:06 PM
#10
Shameful Thread Killer
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Every driver, every mission, every car is different. It's a use-case determination and there is no right answer. Measure them with a mic, look for cracks, and propagation. Decide if you need that N-th limit of brake authority. No right or wrong answer here.
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Ratchet1025 (12-28-2019)
03-14-2018, 02:42 AM
#11
Rennlist Member
The wear limit is 1mm per surface, 2mm total. So if they are 28mm new, the wear limit is 26mm and should be replaced.
12-27-2019, 04:43 PM
#12
Rennlist Member
At what remaining pad thickness is it recommended to change pads? I had my 996 in for smog this morning, and tech measured 6mm front and 8mm rear. Also, the owner's manual refers to the Maintenance Booklet / Maintenance Schedule. I seem to have a fairly complete set of documentation (3rd owner) but see nothing that is Maintenance Booklet / Maintenance Schedule. Anyone know where I can find a PDF of that?
12-27-2019, 09:37 PM
#13
No reason to replace pads until they're down to ~1/8" (3mm) of material remaining. They'll fail state inspection at or below that limit. Of course if you have OE pad wear sensors installed, they will bark at you long before that and encourage you to waste perfectly useful pad material 
I disabled my sensors long ago.
I disabled my sensors long ago.
12-27-2019, 10:24 PM
#14
Burning Brakes
Replace separately as needed. I swap track pads and street pads myself before and after track events. Swapping pads is not difficult, so if the shop you are using wants to replace both, just buy a set of pads and do it yourself or find another shop to do it for you. Measure or have measured the rotors and visually inspect for cracks though.