D'oh

Well, just took a coworker to the local Nissan dealer to get the brakes on her XTerra replaced. As usual, the dealer said that the rotors needed to be turned or she might feel pulsing during braking. I never got to see the rotors before hand, but afterwards they looked very nice.

Now, I've been to 5 track days, and have replaced my rear pads twice (on my third set now) and my front pads once. In that time I've never turned the rotors, although I'm starting to see a significant groove on the front disks where the pads rub. The groove is probably 0.03" deep or so, and is consistent over the swept area of the pad.

Since I never got to see the brakes on my coworker's truck I don't know how they compared to mine, but since she doesn't track her XTerra, I'm guessing her rotors were not as worn as mine are.

So, after all this, I have a couple questions:
1. What exactly is turning the rotor supposed to accomplish?
2. How do you know they need to be turned?
3. If you don't turn them when they need it, what happens?

My thoughts are basically that turning the rotors is something any shop recommends just so they can pad their fee (whether the rotor actually needs it or not), but I'd like some feedback so I can better judge when I should quit doing my own brake jobs and have someone turn my rotors.

EDIT: From the few articles I've read so far, it looks like most performance brake companies actually recommend that you do not have your rotors turned. They want you to keep as much rotor mass and strength as possible.
END EDIT

EDIT AGAIN:
Here's pretty good article:
http://www.aa1car.com/library/2003/bf110322.htm
END EDIT

Any thoughts?

-D'oh!

Q45tech

Modern rotors have a flatness [across the face parallelism] spec of 0.001", older specs back in 90-2000 were 0.0028" for most Nissans.

Anything greater can be felt as a quiver in the steering wheel when brakes are lightly appplied at 65-75 mph.......brake pedal pulsation requires an out of spec flatness great than 0.003".

A individual driver sensitivity compliant issue.

Most Nissan brakes are designed for average insensivite drivers and the rotors are too thin and light weight for durabilty. For people who might make a panic stop from 75 mph one every 5 years. Not someone who might engage in track events or serious mountain driving near the limit.

The Extera is kind of self regulating in those regards.

Common on Nissan to resurface the rotors at least once per year to get rid of vibrations.

On my Q, I resurface every 7-8,000 miles but I am a perfectionist regarding brake feel........most look at me as a nut.

People with cars with superior brake designs [Brembo big thick rotors] are lucky...........they can go a year between resurfacing.

Q45tech

As to resurfacing if you turn them when they are only 0.005" out you have the ability to resurface 8 times [less natural wear] befre you reach the limit [1mm wear limit].

The longer you wait the more you have to remove to return to spec. The usual metal thickness is 10mm per side so 1mm is 10% and the edge metal is 60% of total rotor weight so from brand new to fully worn is a 6% reduction in total weight! This weight reduction will increase rotor temperature by roughly 6%.

A single 80 mph panic stop might raise rotor from 100F to 600F with worn out rotors it might be 636F even 650F.

The factory assumes worn out rotors equal [go along with] worn out thin brake pads which allow more heat to transfer [radiate] to the brake fluid thus the potential for fluid boiling and brake fade much earlier with worn rotors and pads.

The pads are 9-10 mm thick when new [insulating the fluid].

I alway change my pads when roughly half worn [3-4mm] instead of waiting till the factory safe minimum [1-2 mm].........pads are cheap ------an accident is not.


Most brake fade is fluid boiling vs pad fade.

The worst case for fluid temperature is 5-9 minutes after a serious stop sitting still! Heat soak from no air flow building up on caliper piston!

westpak

iTrader: (19)

The only reason to resurface is if you actually feel a difference in braking like pulsating, and that is usually due to uneven pad material on the rotors not warping. If you go to the track and bed ther pads in properly you probably don't get uneven material as the track pads are harder and remove the pad material.

In my opinion resurfacing rotors is a waste of money and just a way to charge you more and sell you rotors sooner.

That being said if yo ugo to the track often you should keep an eye on the rotors not so much for resurfacing but because of thickness, if they get too thin they will not handle heat as well, so after 5 track events I would think you are probably ready for some new rotors.

Q45tech

Of course you don't just cut the rotors unless you have the symptoms and measure the rotor runout with a dial indicator.

Different vehicles have different rotor quality and brake design.....many times rotor warping is caused by wheel hubs bending a 0.0003" which get multipled out to rotor edges. Why they invented on the car brake lathes which should be used with Nissan performance models.

Many non precision brake shops may make the problems worse with off car external brake lathes.

I measure my own runout and decide how and who is going to do what mostly I spend an afternoon fixing my own situations, since most won't take the care I demand.

I usually get 40-50k out of my rotors which is long enough.

Fixed 4-6 piston usually provide more even pressure than more warped prone floating caliuper systems but fixed have more rigorous requirements to not feel runout.

D'oh

Thanks for the responses guys. Sounds like it really does come down to personal preference as long as you still have good rotor mass. I figure I'll keep running my rotors until I expose the fins

-D'oh!

spf4000

If you track your car, you really don't want to be grinding your rotors--the only thing you will do is weaken the rotors, which will lead to warping and/or cracking.

Also, if you track your car heavily, you'll need to replace your rotors every few pad changes. This is especially necessary if you use race pads.

Jason@Performance

iTrader: (11)

it all depends on how much thickness is left onyour rotors... Most OEM rotors when it is time to replace the pads can not be turned because they will be thinner then spec calls for...

The pads are not going to make full contact with the rotor if there is any rotor wear that is un even. this will cause noise, uneven braking, and will also decrease the life of your new pads and your already worn rotors...

would you put used pads on your new rotors? and cut into your new rotors so they are un-even from day one?