Brakes Question...

The shop I take my Porsche to just told me I am going to need new pads for my front brakes soon. No big deal but they also told me that in order to make sure I don't get any squeel once they are changed that I should also have the rotors changed out. They said they can't be "turned" since they are cross drilled. Does anyone know if that is true? It seems that if you have to change the rotors whenever the pads are changed that it would get REALLY expensive.

NOT true! Brake sqeal is due to poor pad seating during light to moderate braking. I NEVER turn my rotors except as required for slight warping or roughness/grooving.

wwest is right. The pad is what is squealing. Also, you shouldn't turn modern performance rotors ever. It will only make the problems worse. For example if they have a slight warp and you turn them, they are now thinner in areas making them even more prone to warp! You should run your rotors until they get too thin (less than spec runout) or they get jiggly from warp. A very slight pulse under light braking is no big deal, so long as it doesn't turn into a shudder under more forceful braking. One more thing: make sure you bed the pads properly! That makes the biggest difference of all. Also, if you change to a different pad compound, give it a few days before using them hard to allow some pad material to bed into the rotor surface. Happy motoring! -Paul

OK...so it is true that the rotors shouldn't/can't be turned but should they be replaced in order to prevent squeeling? The car barely has 30K miles and from what I can tell the rotors look like they are in pretty good shape. I do not feel any pulsing or problems at all. I just don't want to have to replace the rotors unless I have to. Are these guys just trying to get extra dough out of me?

My BMW service rep., who always seems to give me good info., told me that if the rotors were still above minimum thickness, they did not have to be changed. He said, however, that not changing them might result in some squealing for awhile, which would eventually get better. I chose not to change them, and sure enough, they squealed for awhile. Within a few hundred miles,though, the squealing was gone. Very glad I didn't spend the money for new rotors.

Porsche dealers typically change the pads and the rotars at the same time primarilly 1) for the ultimate in safety for an ulta high performance car and 2) because they make more $$ than on a standard brake job! Just like for the pads, there are specs for the rotors. If they are 'in spec' they dont need to be changed. However, the dealer may refuse to do the brake job if you dont change the rotors. I would like to know what they say .... BTW, ETTSN, what is bedding the brake pads?? thanks

Well this is not the dealer telling me this...it is an independent shop that does a lot of older Porsches. I am going to ask the dealer for their opinion though... Like CAndrew says I may just have the pads done and if they squeel for a while that is fine. If they continue to squeel I will then have the rotors changed out...

Well as long as if you turn them and they are above min. thickness I see no problem. If the issue is whether the holes might get a crack then that's valid but otherwise I don't see a problem. I have been doing it for years. The squeeling is definitely the pads, with the brake dust and pad material not mating completely flat to the rotor. For replacement look at the minimium thickness of the pads and rotors. Don't go by anything else unless you are upgrading for the sake of a better pad or floating rotor or something.

Rotors do not make the squeal, it is the pads, or material from the pads, or the anti squeal dampers. If there is pad material stuck to the rotor surface then they can be cleaned with a slight turning... again not enough to go below minimum tolerance. Rotors only need to be replaced if they are outside the thickness tolerance, or if the lateral runout is to great, or if there are cracks between the cross drilled holes over 7 mm long. (per the service manual)

Once again, Loren gives perfect advice! Bedding the pads refers to the mechanical 'mating' of the pads to the rotor surface. The best way to do it is to find a big empty parking lot near where you swap the pads (and drive very easy on the way there). Start with a few medium pedal pressure near-stops (to about 5mph) from ~30mph, then move up to heavy pressure at ~60mph for 2-3 more. Let them completely cool (only a few minutes from these speeds. It's best to keep moving very slowly while cooling, but if you park do not engage the parking brake! ). This allows the pads to settle into the calipers and begin depositing pad material to the rotor. Then warm them back up with 3-4 medium near-stops from ~30mph again, followed by 6-8 very heavy stops (near ABS onset) from 60+mph. Once again, let them cool completely. Your pads are now primed for repeated heavy stops without glazing! -Paul

The independent shop I use measured my rotors. Since they were within spec, they did not recommend changing the rotors. They showed me the specs and let me watch while they did the measuring. Good luck, Mike

Sounds like an attempt to increase profit margins. Loren is spot on - there's no reason to turn the rotors.... but if you want to "de glaze" the pads the easy way, buy the set of pads, and heat them in your oven.... it works, but gosh, what a smell!!!! (doing this evaporates the thin layer of mold release compound which can cause some squealing). Jeff