Joe Still

Have slight front end shimmy under moderate braking that's gotta be warped rotors (93 FD). Car has 40k and rotors have bee turned once. I don't mind getting new ones but wonder if this is a part best had from:

Dealer-Factory original
After Market- they say they equal
Upgrade after market-slotted etc.

I autocross average 4 times a year. Other than that Ijust enjoy spirited street driving.

Suggestions?

FormerPorscheGuy

Honestly, I would go with the aftermarket. Brembo makes a nice set for our cars. Plus I have heard that the factory originals are expensive when replaced with new one's.

phlanigan

I got a set of fronts for $43 ea from alloemautoparts.com. I autocrossed on them about a month ago and had absolutely no problems. They are solid surface Brembos and came in Brembo packaging.

rynberg

Just get some Brembo blanks. The cross-drilled WILL crack on the track but apparently are fine for street driving.

ExpensiveHobby22

that's some good info phlanigan, thanks.

shred

Saw some RX7 stuff on Ebay today that included some front and rear Brembo rotors. Believe that they were both drilled and slotted. One guy was selling a package of front and rear, some other was selling pairs only, front or rear. Stock size so you don't need to replace anything.

The ebay link for the set here-

I wouldn't bid on them at this price, will probably be lower next time they go around if they don't sell.

Fronts only

Here are the fronts only, pretty good buy it now price on these. Don't know the guy or the manufacturer of these but, you can always email him. Search on rx7 and rotors, will come up with some good stuff.

Anyhow, just an option if you want to use it. I usually find some cool stuff here every once in a while.

RonKMiller

Why not just turn them again? They should still be in spec even after a second turn.

shred

Believe that Ron is right. I kill my brakes. Brake rotors and pads are cheap compared to turbo rebuilds and other garbage. I never down-shift, just kill the hell out of my brakes.

So if you can get a good turn out of them, I would do it also unless they were miced as too warped to turn again. Unless you are going to get some bigger rims and some larger rotors, better calipers, just keep grinding what you have. A good set of pads will give some decent performance stops (not as many as an upgraded system before fading) but it is cool until you upgrade the whole thing.

911GT2

This may seem like a dumb question, but i can't figure out why turning the brake rotors does anything. Do you rotate them about their normal axis of roatation? If you do, and i can't see any other way to do it, then that seems like it would do nothing, because they normally rotate that way anyway, and all 360 degrees of the rotor ar still swept through the caliper. Do you spin them so the side that was on the inside is now oustide?, and vice versa?

Jammer5703

I have the brembo dimpled-slotted rotors, ss lines, and hawk pads, definitely not too bad.

shred

You don't really 'turn' them, you have a shop grind them flat again.

The Car-Tech term is 'turning' your rotors but they really put them on a small device that spins them and a cutter (a lot like a potatoe peel cutter) slowlly takes off anything that sticks out. This will make the surface flat again and take out the warping.

Only problem is that you can only take off so much until the rotor is so thin that it cannot keep itself cool enough under braking from cracking, melting, warping severly causing an accident of the worst kind.

So mechanics will take a micrometer and 'mic' your rotor to tell how much they need to take off. They break out the big book (most know off the top of their head) to see the minimum width for your rotor, if they need to grind it past this minimum width to get the warp out, they won't do it and tell you that you need a new rotor (if you get one, get the pair either both front or both back!).

Hope that helps.

maxcooper

Most rotors have the minimum thickness specification cast right into them.

I have warped a bunch of rotors in my car. My last set were some rears, probably from using the parking brake on hot brakes. I don't use the parking brake at the track, but I think letting the car sit with hot brakes can lead to "warping" whether the brakes are on or not. My suspicions about what causes the warping are that you stop and get one part of the rotor hotter than the rest, and it expands accordingly. Then you go use the car and when you brake it tends to take more rotor material off the hot spots, which are now higher than the rest of the rotor. When it cools back down, you now have one part of the rotor that is not as thick as the rest. Turning the rotors seems to fix the problem, but with even less rotor mass, the brakes will fade faster and you are probably even more likely to warp them again.

If you track the car or really make the most of the brakes otherwise, don't get drilled because they will crack (see numerous posts on this topic in the Suspension forum). EBC's recent switch from drilled to dimpled was reportedly to keep the rotor cooler, so perhaps the holes screw up the cooling a bit, too. Slotted are supposed to be better from the cracking standpoint, and you probably get the same bite that you would with drilled anyway. For best durability, solid-face OEM-style rotors are surely to last the longest. Combine that with a cryo-treatment and you will get even more life. I tried cryo (from http://www.cryoscience.com) on some Brembo blanks and they lasted longer than other Brembo blanks that I had used in the past. They were still good but just starting to get heat-check surface cracks when I removed them to install a big brake kit. Anyway, cryo seems to help extend rotor life significantly.

The OEM Mazda rotors are high-quality, and may be worth the money if you end up warping a bunch of cheaper replacements.

-Max

Joe Still

Good advice- Thanks to all. I believe I'll start with a set of aftermarket oem type. I've heard drilled do break some and without pad upgrade doubt the dimpled or slotted will improve my performance.

rotary-tt

cryo treat the stock rotors and don't sit still with them hot like Max says. So if you autocross, try to drive the car around the lot for a minute after your run to cool them off evenly. Racing on the street and coming to a hard stop will also warp them...

Joe Still

Are cryo treaters easy to find or is it like the downpipe coaters where you send items off?

Joe Still

forgive my efforts- trying to figure out how to post pics

GoRacer

iTrader: (2)

Change your pads, this is what causes them to warp. Get the right pads for your rotors.

You can turn your rotor a bunch of times before it gets too thin. I had green stuff pads and had to turn the rotors three times before I got rid of them for stock and haven't turned them once since.

I have both slotted and cross drilled Z-Speed rotors on my Honda and they have never cracked under sprited street and street/strip drag (no auo-X track though).

With the cross drilled you loose alot of surface area, the slotted you loose less. The benefits are no slipping in the rain otherwise i've not noticed the difference.

rotary-tt

Cryo treating the rotors is proven to give about 300% more life. www.frozenrotors.com is one place but they aren't the cheapest. Just do a web search on Yahoo!

Tom Delegram

Joe,

Going to cross driled and /or slotted rotors will bump you up to AP. I did not see any mods so I don't know what class your running. Just an FYI. I have seen the moron protests first hand.

tom

Joe Still

I've been in S Stock as I've made no mods to date. I do have autocross gummies but the size is stock and they were allegedly DOT approved before they were turned down.

I see some of these guys work magic with different combinations of aftermarket and mods but for every success it looks like lots of disappointments.

jeff48

Here is a good site for information on myths about brakes
http://www.stoptech.com/whitepapers/...otors_myth.htm

GoRacer

iTrader: (2)

Quote from "jeff48's" web link above:
[/quote]In fact every case of "warped brake disc" that I have investigated, whether on a racing car or a street car, has turned out to be friction pad material transferred unevenly to the surface of the disc. [/quote]

The crossed drilled/slotted rotors make a huge difference in the rain. It keeps your brakes from slipping (similar result as anti-lock). The drawback is you loose surface aerea.

martini

these guys sell brembo's for fairly cheap:

http://catalog.thepartsbin.com/?AID=2331353&PID=1251091

RonKMiller

Good stuff. Required reading for everyone. I still get goosebumps when I think of Carroll and his cars...

Now I know that I don't need to go out and do an expensive brake job every time I start to feel a shimmy -all it takes is a some garnet paper, a little elbow grease and a couple of high speed runs.

Thanks jeff48! Just when I though I knew everything...

RonKMiller

Oh, by the way - Max DOES know everything.

Parking brake - whoda thunk??