Brake Vibration Under Heavy Use
 

I'm generally not too hard on the brakes on my car, but there are ALOT of windy, cop-free roads out where I live, so from time to time, I'll take my car out and drive it like it's meant to be driven. :D I'm fairly hard on the brakes during this little "session" and I've noticed that after hitting a straightaway at about 180 Km/h or so, (that's with a tailwind, and downhill,) and reefing on the brakes they will start a small vibration, and the pedal seems to "float" right before the car comes to a complete stop. I'm aware of the gasses, etc. produced (reason for cross-drilled / vented rotors) but why do I feel a vibration? The brakes do get very hot, but heat alone shouldn't cause this should it? I'm careful not to warp my rotors either. I always continue driving for awhile normally to get some air flowing past them and cool 'em off.

Please, no one lecture me on using my brakes or anything, I'm just asking a question petaining to my brakes, not my driving style. ;)

Thanks in advance!

i get the same problem when doing some hard driving myself....my friend suggested going for some dot 4 fluid(higher boiling point) and some steel braided lines...he also suggested cross drilled or slotted but the first option is ALOT cheaper and should help some....he also suggested using a little engine braking to slow down from really high speeds,but i think this would cause unnecessary tranny wear and tear.. whadda you think?

I thought this at first too, but I only notice it under really hard braking, and only after the discs are really hot. I know this can warp them, but if they're already warped, I should feel them during any braking situation.

If you've got under 20,000 km on your ride Mazda will replace the rotors free.

Been there, done that :D It's considered a defect from factory or shipping if it happens before that amount of mileage. Sweet I say :D

Nice! :D

Heat makes rotor warping more apparent, hence the vibration.

The "floaty" feeling is either brake fade or boiling brake fluid. To fix the first, you need high-performance pads; Hawk, Porterfield and EBC make good ones. To fix the second, replace the brake fluid with Castrol GT-LMA if you're cheap, Ford High Performance fluid (from your local Ford store, in the blue metal can) if you want to spend a little more, or Motul if you like spending a lot :D

Contrary to popular belief, slotted/drilled rotors will not do anything to fix your problem. They are cosmetic only.

Actually, the slotted / drilled rotors decrease your stopping distance significantly.

When you really reef on the brakes, the pads will heat up to a point where they actually form a gas byproduct from all the friction. This gas builds up, and actually pushes the pads away from the discs, in effect decreasing the amount of pad touching the disc, and therefore, less friction is availalbe, stopping distance increases, etc. The slotted / drilled rotors help in two ways: They are drilled in order to allow more heat to escape, thus helping to prevent the gasses from forming in the first place, and they are slotted to allow the said gasses to have some way of escaping, instead of building up between the pad and disc, thus increasing braking performance. They're not just for looks! ;)

Hope this sheds a little light on the subject.

im not sure if this is an uncommon thing among cars that are stock....

ive driven my fair share of cars up past 120mph, from a z3, m3, rx7, various eclipses, civics, a probe, my moms regal (only could do 110 because of govenor) and of course my car...... all had this similar reaction when i started to brake from high speeds....

so i figure it must just be the brakes getting hot and grabby or something....

Actually, you just rehashed most of the popular misconceptions about drilled and slotted rotors. Check the following link and scroll down to the bottom....

http://www.baer.com/faq.shtm

This company is one of the top manufacturers of REAL race car brake systems in this country. Although they sell drilled rotors, they state that they are offered "as a cosmetic option only." They didn't even sell them a few years ago but they caved in to market pressure :)

Basically, outgassing USED to be a problem in the 60's and 70's when almost all brake pads (including "high performance" ones) were organic. You can still get these pads at discount auto parts stores, but outgassing is not a factor with modern carbon pads or most good metallic pads (like the ones that come on all Mazdas from the factory). Unless you paid $9.95 for your pads at Pep Boys, they don't outgas :D

Drilling a rotor causes several problems. First, it accelerates brake pad wear because the holes scrape away the pad material when you brake. Second, the holes cause stress cracks. Third, the rotors will usually run HOTTER because of decreased heat-absorbing rotor mass. Fourth, the rotors wear out faster because of decreased surface area. Slotted rotors don't suffer from the second problem, but still suffer from the others.

The only stock-size rotor upgrade I've seen that IMHO is worth a damn is cryo-treatment (i.e. deep-freezing) which hardens the rotor and decreases wear.

In short, don't believe the hype :D Any questions?

Chris, I don't disagree, but I actually like the fact that slotting helps remove a bit more pad material. If your hard on your brakes, this can help prevent the pads from glazing.

Well, yeah, there are a couple of benefits to drilled/slotted rotors. This is one; the other one is marginally better wet braking because the water squeezes out the holes/slots.

However, IMHO the costs still outweigh the benefits, esp. when the main advertised benefits- shorter stopping distances and less fade- are :bs: To get a *real* improvement, you need either (a) new pads [cheap] or (b) larger rotors [$$$] :)

The first step should be new pads- modern carbon kevlar pads absolutely will NOT fade. The temperature they have to reach to start outgassing is higher than the melting point of a brake rotor :D

Soooo, do what I did. Compromise and get larger diameter rotors for increased stopping power AND cross drilled/slotted for good looks behind those large diameter open wheels. ;)

This might sound stupid but how about ABS. Under hard breaking the pedal starts to shake. You can feel it clearly under slippery conditions.

But if you've got warped discs, it's possible that they feel normal in a normal breaking but under hard breaking the pedal starts to shake. I just changed new discs into my gen1 because of warped discs.