: Do I have to change the brake rotors?



Shaun V
01-08-13, 06:59 PM
2004 CTS-V: The dealer says that I have to change the rotors every time I change the pads. Is this true? Is there a less costly option? Thanks!

carlson_mn
01-08-13, 07:19 PM
No need to do that. Bring them to your local auto store and they will measure the thickness and you can choose to have them turned or replaced.

Either option will be about 1/4 the cost of dealer parts. The dealers recommend that because they don't want to deal with the 1/10 cars that end up with noise or other issues when they keep the rotors, not to mention most Cadillac owners are probably easy to squeeze money out of.

SevillianSTS
01-08-13, 07:27 PM
Absolutely not.

I would look at them and analyze the old ones first, but in my experience usually you can change the pads at least once without changing rotors.

Really just comes down to what kind of shape the rotors are in at the time of the pad change..

darkman
01-08-13, 07:29 PM
The dealer is essentially correct, although there can be exceptions. As indicated in the specifications (see attached) there is very little difference betweeen the minimum rotor thickness and the rotor thickness when new. This means that the metal available for removal by turning the rotors is quite small. So if you run the pads long enough to wear them out, the chances are high that the rotors will be too rough to smooth out by turning.

It is conceivable that the rotors could be turned once.

Finally, some folks will run new pads on a old rotor without turning them. This will work, but braking power is reduced as compared with new pads on smooth rotors.

SevillianSTS
01-08-13, 07:45 PM
Hey Darkman, one of my rear rotors is cracked. I was thinking about going with the factory drilled / slotted all the way around, and my pads are still good all around, can I used the existing pads on new rotors, or should I change those too ?

darkman
01-08-13, 07:52 PM
Hey Darkman, one of my rear rotors is cracked. I was thinking about going with the factory drilled / slotted all the way around, and my pads are still good all around, can I used the existing pads on new rotors, or should I change those too ?

You can use existing pads on new rotors. You should to bed them in just like they were new pads.

JDB
01-10-13, 10:31 PM
OMG...I hate dealers or any mechanic with this attitude...

If there's meat left above min spec, why would you need new rotors?

Bacon V
01-10-13, 11:22 PM
HA! Oh man my front rotors are way overdue by that chart. I knew they were worn but could only get pads and wanted to get it back on the road. Rotors looked good and had no warping, but they had a very noticeable lip on the edge. Guess Ill replace those soon...thanks for the docs Darkman, I appreciate every one of them.

AAIIIC
01-11-13, 10:40 AM
No, you don't need to change the rotors, unless they are at the minimum thickness. Turning rotors is just a waste of time, energy, and useful rotor material, so the explanation that the old rotors can't be used because they need to be turned is BS.

The last time I had a set of rotors turned was March 2000 - I remember, because I had pads installed before my first ever track event. The 2 cars I had back then I still have 12 years later, and I added the V in late 2007. With all of the track days, brake swaps/upgrades, etc over that time, I can't tell you how many times I've changed out rotors or pads. If I'm changing pads and using the same rotors, I just use a scotchbrite pad on a drill to scuff the surface of the rotors to give the new pads a rough surface to bed into. Works like a charm and takes all of about a minute per rotor.


Finally, some folks will run new pads on a old rotor without turning them. This will work, but braking power is reduced as compared with new pads on smooth rotors.
Poppycock. I mean, that may be true for the first couple/few days, but after that there's no difference. Based on my experience, even with new pads on new rotors, if you look at the wear pattern during the initial driving, there is not 100% contact - you can see swaths of the rotor that the pad isn't even touching yet. So it's no different than using new pads on old rotors.

GreaseMonkey
01-11-13, 11:37 AM
Brake pads and rotors both transfer material to each other, which aids in friction ultimately aiding in better braking performance.

That being said, you CAN put old pads on new rotors, or new pads on old rotors and the car will still stop. Hell, I've seen cars with the pads completely gone that will still stop with just the metal brake pad backing plate.

I personally don't recommend turning rotors. There is a small window between minimum discard thickness and the thickness rotors start at. If you don't have any pulsation, what you can do is just take a die grinder with a 3M scuff pad and clean up the rotor surface. Turning a rotor for a new set of pads is just being performed to take off the material that is transferred onto the rotor from the old pads so the new pads can bed in. It's not a very thick suface, and turning usually takes more material off than need be. Just scuffing them up with the grinder will take the material off and put a non-directional finish on the rotor so the new pads will bed in.

mackey
01-11-13, 02:16 PM
when i raced motorcycles, i rarely if ever changed rotors when i changed pads but i always bead blasted them if i was changing mfr or compounds. i will also say i also changed fluids frequently (< 1k mi), cleaned the pistons annually if not every 6 months and inspected the brakes very often.

is it a good idea to change them at the same time? sure. is it absolutely necessary? no, but you should take the opportunity to thoroughly inspect the entire braking system while you are changing the pads and R&R as necessary. if youre not doing the work yourself, then youll have to take their word that its time to replace them whether they measured them or they didnt.

YMMV

Shaun V
01-12-13, 04:16 PM
Thanks for the advice!

UnsafeAtAnySpd
01-13-13, 03:39 PM
I've gone through around 8 sets of front pads in the past 50k miles. I haven't gone through 8 sets of front rotors in that time...

JDB
01-13-13, 07:50 PM
I've gone through around 8 sets of front pads in the past 50k miles. I haven't gone through 8 sets of front rotors in that time...


Yeah, Waste of $ to replace rotors with every pad. I'm still on the original set of rotors all around. Multiple sets of street and track pads worn out and swaps. If its about min spec, there is NO reason to replace. If you say "warped" or have vibrations, I bet its just pad material transfer that needs to be knocked off. Brake hard a few times to re-bed the pads. Done. $ saved.

barrok69
01-14-13, 06:15 PM
If the DTV (Disc Thickness Variation) on the current rotors is high and you have any kind of grooving you will wear out the new pads rather quickly and be prone to more noise, dust and vibrations in the brake pedal giving the perception of a "warped" rotor. Turning the rotor will help with this and also give you a clean slate to bed in the new pads properly. Most rotors these days are manufactured as throw aways due to min thickness specs and don't leave much room for turning.

Depending on how sensitive the vehicle is to DTV a rotor change may be the only option to ensure a vibration free driving experience.

For somebody looking to get the most out of their brakes, New rotors would be the best option. Not only do you get a fresh clean surface to bed, but you get more effective mass for dissipating heat from the system keeping pedal feel more consistent and less prone to fade.

Using an old rotor also has a downside. If you did have uneven pad wear on it, and you "scrape it away" or turn it, there is still a chemical reaction that goes on behind those spots and changes the material properties of the metal making it more brittle and likely to generate more hot spots during braking events and will prematurely wear out any new pads you put on and also lead to more vibrations.

V8V
01-22-13, 01:59 PM
I had mine turned after 150k highway miles when I changed the pads because one of the pads was starting to de-laminate. The guy that did the work commented several times on how hard the metal was compared to other rotors. I think it was about $30 total, with no obvious change other than the chirp that disappeared with the bad pad.