Kento

Yes, I have searched, but the only thread that came up was inconclusive.

The brake system on my FD is entirely stock at this time, and since I'm only the second owner, I'm virtually positive that it hasn't been autocrossed or "track day" run (the previous owner was an engineer who was extremely **** about the car). The FD has only seen street and the occassional aggressive canyon drive, and I can't say there were any instances where there was extremely heavy braking for long periods of time. Braking has only been moderate for the most part (well, in my opinion at least...) since you can't drive on the street like you would on a track. Yet I notice that if I brake hard from higher speeds (say 80 mph), that a vibration appears. I haven't noticed any pulsation through the brake pedal. Wheel weights are all intact, and not enough mileage to alter balance. Wheel bearing and suspension components all seem in excellent condition after the usual cursory inspections.

Are the FD discs very susceptible to warpage?

jumprdude

Not particularly, but some bad habits can cause the rotors to warp.

If the lugnuts were overtightened (very common problem) that may cause the rotor to warp.

Lunar7

In my experience the front rotors do tend to warp on/after hard usage (120+ mph stops).

Just turn them and they will be good again.
RX-7 brakes were designed to be as light as reasonably possible, so extra heat sinking ability for extreme use is not part of the equation.

If you upgrade to 99 spec RS brakes you will be amazed how much heavier the rotors are.
Of course the bigger heavier RS brakes stop much better and don't warp.
They could be considered overkill for most street driving due to the unsprung weight penalty and the fact they engage ABS so easy.
Considering that, I can understand why Mazda went with the lighter brakes untill the RS came out.

artowar2

If you haven't done it, I suggest that you try loosening, then retightening the lug nuts with a torque wrench (and a proper sequence). Then see whether you still have the problem.

Kento

When I installed the Fikse wheels, I tightened them to the proper torque (66-86 ft./lbs.), and in a criss-cross sequence. Just to be sure, however, I retorqued them all-- and the vibration still exists. I noticed that the vibration doesn't appear unless the braking is from a speed higher than 80 mph, and and it occurs whether the braking is moderate or heavy.

Guess it's time to get'em turned, and/or upgrade the package, eh?

RonKMiller

OK, this goes into the urban myth category: Brake Rotors Warping.

Does not happen on street driven vehicles, and rarely happens even on race cars.

What you are feeling are deposits that have built up unevenly on the rotors from LIGHT braking. What you think is a "warped" rotor is uneven deposition of this crud, hence the pulsation.

You can turn the rotors (everybody ignorant does this) but usually you can take care of if by polishing the surfaces of the rotor with emery paper - it's the only thing hard enough to cut this stuff, which is actually an iron based deposit. I've had great success with a palm sander just holding moderate pressure on the faces while you spin the wheel (or have a helper do it) for a few minutes.

After you have removed this stuff you can then re-bed the rotors and brake pads by doing 10 progressively slower hard stops from speed. You are trying to get the rotors really hot. Once you've made your last run park the car with the parking brake OFF. You've just re-bedded the rotors and shoes.

RX7Elmo

To double check warped rotors, i would jack the front up,a nd turn the wheel. if you hear/feel resistance in a certain area, it could be a warped rotor.

Kento

Jacked up all ends of the car, spun the wheels, no resistance or weird noises.

Ron, I will try your solution. Is there any way to keep this buildup from reoccurring? (other than braking like a maniac all the time...obviously not an option) Upgraded brake pads?

ZeroBanger

just get brembo slotted drilled rotors. My FD rotors were warped when I bought the car, had them turned, 10K later warped again.

Lunar7

If this works please post back here and state that your problem is solved.
This could be good advice but the statements about brake warp, and ignorance of people who turn rotors seem a bit off.

Are you saying that the brake lathe is not cutting away warp induced distortion but rather deposits on the rotor surface?

If only ignorant people turn rotors, then I guess products like "Brake True" are for the divinely intelligent.

RonKMiller

The emery paper will only work if the deposits are small and this just started happening. If this does not work Blanchard grinding is about the only thing to do, unfortunately, the cementite (the iron deposit I was talking about) is so freaking hard that the relatively soft surface of the disc will cut unevenly and the problem will reappear in a little while. Its kind of a vicious circle.
Oh, btw, the cementite is pretty much invisible - think of it as a thin layer that is welded to the surface of the rotor.

If you go the grinding route then proper bedding in - as described - should help to eliminate the problem. If it doesn't (and this happens alot) new rotors are the only solution - but - once again they need to be bedded in properly right from the start.

I've seen guys grind and re-grind and spend a lot of money on different compound pads and rebuilds only to have the problem appear again and again. Once this happens it's kind a downhill spiral that only - you guessed it - mo' money - will solve!

RonKMiller

Yep, that's exactly what I am saying.

You are grinding off deposits of friction material that have been unevenly transferred to the surface of the rotor. That's exactly what causes the variation on the run out and has everyone running around saying the disc is "warped". No way, no how, can't be done.

Cementite is the iron carbide that forms from the process of these deposits being heated to extremely high temperatures. You KNOW how hard carbide is.

I think you need to understand the true meaning of the word ignorant - uneducated is what I am trying to say. There are plenty of ignorant mechanics running around out there with pre-conceived notions that have been handed down from generation to generation - incorrectly. That's why I said this falls into the category of urban myth.

Did you hear the one about cell phones causing gas station fires?

RonKMiller

Yep, no doubt it would cure the problem - but your problem was not warped rotors.

It's the most expensive route to take, but once again, without proper bedding in of the new pads and rotors it can happen again - guaranteed.

Now you know why brake shops are as common McDonalds.

SleepR1

The stock US-spec FD rotors have not warped with hard use. I'm now using the Type RS rotors with hard use, and they are also very good...

RonKMiller

Ahhhh, thank you berry berry much. Someone who finally understands.....it is all about brake PADS.

DamonB

Mine get punished constantly and I have never warped a rotor. Apparently this is one case where Ron is NOT lazy and he uses some elbow grease I take the easy way out and have mine turned but I go to a good machine shop that understands I really just want them "skimmed" as little as possible. They double check for warping (never had any) and then basically just renew the surface for me.

Bedding in of the pads is very important. I apparently didn't do a good job the last time I changed them and they are squeaking like mad along with slight pulsing through the pedal. Off come the rotors...

redrotorR1

Agreed. I absolutely abuse the brake rotors on my FD and I've yet to encounter a warped rotor. I've even put on used brake pads that were unevenly worn and not seen any signs of warping. (Although the prolonged squealing taught me a valuable lesson ... ) One year of regular auto-x and a few time trials/hot laps .... nada. And, if I'm not mistaken, these are the original rotors that came with the car! (I have the rusty centers to prove it. )

The_7

why do you have to bed-in the rotors? why are bare rotors more prone to this carbide problem than a rotor with a thin layer of brake pad material? does it have to do with the bedded in rotors being able to dissapate heat faster? also, why does over torqueing the lug nuts damage the rotors?

artowar

iTrader: (1)

Here's the frequently referred link to the Stoptech Warped Disk Myth article:

http://www.stoptech.com/whitepapers/...otors_myth.htm

And a link to their other technical articles:

http://www.stoptech.com/technical/

dis1

Just thought I'd add my experience with warped brake rotors. My first set (stock) became so badly warped that even the hats were warped. (Deposits my a$$!) They were so bad the place I took them to get turned said the machine couldn't even mount them properly. Anyway my second set also started to warp on one side. (Brembo slotted.) This was due to a bad wheel bearing. In regards to stock rotors easily warping I use to believe this but now I think it has more to do with the stock pads. When I had stock pads they would fuse to the rotors after a hard stop very easily, which leaves behind deposits. Deposits alone can cause a pulsing feeling but can later cause a warped rotor. For those that say warped rotors is a myth they would rethink that position if they have seen what I have.

DamonB

That is more than likely due to improper (too much) lug nut torque.

To warp the hat from heat the disc would be so far gone that it probably wouldn't even pass through the caliper any longer.

cavellm

I had the same wobbling issue. 80+ braking and the steering wheel and shifter would strongly vibrate, but not the peddle.

I also had some bad brake fluid (don't ask me how...). A bleed, then suck EVERY bit of fluid from the reservoir, then bleed again fixed this. The pistons were sticking and my brakes were constantly on. Plus a new set of HPS pads. Still had plenty of pad left, but these are a lot better.

But the sqweak a LOT. Got some brembo rotors ready to be installed, hopefully with proper bedding, that'll stop the noise.