Front rotors?

brad98S70 · Post by **brad98S70** » 01 Feb 2012, 06:43

My 98 S70 (133k) had new front pads and rotors at 106k 2 1/2 yrs ago. I really don't check brakes often but I noticed the rotors look like the pads had a wire comb on them making many circular grooves in the rotors. Outside and inside of the fronts. What's happening here?
Brad98s70

Post by **jblackburn** » 01 Feb 2012, 07:17

Road crap (gravel, sand, etc) gets caught in between the pads and rotors and digs into the rotors.

It's not pretty, but as long as the rotors aren't shaking or you don't feel like braking function is reduced or whatever, it's really nothing to worry too much about.

Post by **fazool** » 01 Feb 2012, 11:27

Rotors will often look ugly. The bare and exposed metal has no protection and it rusts FAST. After a rain, my rotors always get orange with surface rust. A couple miles of driving and they are shiny again.

Scratches and score marks aren't too worrisome. If they are really excessive you will lose surface area for braking contact.

Once that comb shape is there, however, it will take a while to remove it. Imagine one single groove caused by a stone or something (as explained above). This will make a groove in the rotor. As the brake wears down on the rotor, the rotor will polish itself down a little. BUT, the pad will conform to fit into this groove and mate somewhat to this shape. Instead of just rubbing on the flat part of the rotor, it will rub on the flat part AND inside the groove deepening the groove as it goes.

If you took the rotor off the car and turned it on a lathe, you would cut/wear down the flat surface until the groove is gone. On the car, however, the brake pads wear down the flat surface and the groove at the same time.

In the first picture is a typical grooved rotor with pad materiual in purple. The second is what you would THINK will happen when the brake works for a while, but the third pic is (an exageration of) what really happens.

brad98S70 · Post by **brad98S70** » 01 Feb 2012, 12:14

Thanks for your replies.. This is possible on both front rotors, both sides inside and out? Rear show normal flat wear. I'm not looking for a problem if there isn't one but seems pretty weird to have matching grooves on both sides...

Post by **fazool** » 01 Feb 2012, 14:03

Well it depends how symetrical they are. Most of a vehicles stopping power is in the front wheels so front brakes are always balanced to do more work. Therefore you can't compare front to rear.

Some manufacturer's brake pads include wear indicators, which are basically soft rivets down in the materal (in a hole) that will start to squeal/ring when the pad gets low (so you audibly know the pad is low). Grooves made from these are exactly located and there is usually two of them (2 rivets) on each side of the rotor.

I have, however, in all my years, never had Volvo pads with those rivets in them, I don't think thats whats going on there.

When you look at the side of the pad, can you see pad material? You should be able to see how much pad is left without even removing the tires.
If there is sufficient pad material (> 5/16") you should be fine and its just grit and debris.

The propblem is that these pads minimally retract and debris can get in there and get held in place.

If you can takle a close up picture showing the edge of the brake pad and the rotor surface and post it here, we can help more

brad98S70 · Post by **brad98S70** » 02 Feb 2012, 07:50

Thanks Fazool for the reply, I will get some pictures and post. I looked, but to my untrained eye, it looks like there's a good amount of meat left on the pads. But one more thing only because I find this really interesting. According to your diagram my rotors will continue to wear deeper into the grooves because the calipers will keep pressure on the pads on those points. Do I have that right? Also if I take the pads out, they will be grooved also to match the grooves on the rotors?

Post by **erikv11** » 02 Feb 2012, 08:03

I doubt that the grooves will get deeper, they just won't get corrected under normal use.

I turn the rotors if the grooves get bad and there is enough meat on the rotor. Like jablackburn said they still stop well when grooved, even with new pads. But will stop better with a flat rotor surface (pads will wear smooth on a freshly turned rotor).

Post by **vjaneczko** » 03 Feb 2012, 10:14

If you can afford the upgrade, I've been using Zimmerman cross drilled rotors and Akebono pads for two years and the rotors are still baby-butt smooth.

Post by **jblackburn** » 03 Feb 2012, 11:36

I have the same combination, but I've warped mine 2 years/40,000 miles later.