Warped Rotor Myth?

[ruudvd]

ik kwam het volgende artikel tegen op internet.

zelf had ik al het idee dat vibrerende remmen niet altijd veroorzaakt worden door daadwerkelijk krom getrokken remschijven. De schijven van m'n xj heb ik destijds op de yj gezet . Op de xj trilden de remmen licht. voordat ik de remschijven op de yj monteerde heb ik ze licht opgeschuurd. Bij de yj was geen enkele vibratie te voelen.

De zj had voor dat ik brakemax remmen monteerde ook hevig vibrerende remmen. Bij nameten kon ik echter geen afwijking meten.

Na een rit met trailer door frankrijk begonnen ook de brakemax remmen ligt te pulseren.

thuis losgehaald schoongemaakt en bewust verdraait tov de vorige montage positie gemonteerd.

resultaat: pulsering voor 90% weg.

　

　

In 40 years of working on cars, 15 years of open track driving, 4 years of racing, and 2 years of racing instruction (which involves safety inspections,) I have NEVER seen a rotor warped or otherwise damaged or affected by over-torqued wheel studs or bolts. I say it's an urban legend.

As far as rotors warping at all -- I don't think I've ever seen one that's truly warped unless it was WAY below spec, and I can count those on one hand.

Unfortunately, you run across pulsating or vibrating brakes, and everyone instantly says "warped rotor" and either they replace the rotor or turn it on a brake lathe and -- poof -- no more vibrations! So they're convinced that a warped rotor was the cause.

It is much more likely that instead of a warped rotor, you have uneven pad deposits on the brake rotor.

When a new rotor is installed the braking surface is just machined cast iron. Once you start using the brakes material from the brake pad is transferred onto the rotor's surface and actually bonds to the cast iron. When installed correctly, this is done by properly bedding the pads.

The bedding procedure is intended to transfer an even layer of pad material to the rotor's surface. This does two things. First, it raises the coefficient of friction between the rotor and the pads, which makes the brakes feel more effective (less pedal pressure is required to slow th vehicle.)

Secondly, and more germane to this discussion, the proper bedding procedure insures that an even layer of material is deposited onto the rotor. A difference in material thickness as little as 0.001" can be felt in the brake pedal.

If you end up with pulsing or vibrating in your rake pedal, especially if it shows up after a brake job, chances are very, very good that its due to the pad material transferred to the rotor and NOT because of a warped rotor.

You can check this with a $30 dial indicator and magnetic base. Just measure rotor run-out at the extreme outer edge of the rotor where th pad doesn't contact and the rotor thus has no pad material deposits. Do this for the front and rear face of the rotor. Any true warping will show up in one or both faces.

So how do you fix a problem with pad deposits? Well, you can replace or reface the rotor on a brake lathe, which is what's done for a warped rotor, so most folks just do that and say that it was a warped rotor to begin with. But, you can also scrub off the old pad material with GARNET paper (not sandpaper or aluminum oxide!!) and carefully re-bed the pads according to the pad manufacturer's instructions.

Bedding in the pads properly is essential to avoiding getting a pulsing pedal in the future. And I'll bet dealerships and other mechanics don't do it properly (if at all). THAT'S why many folks end up with pulsing, vibrating brakes miles down the road.

Case in point -- Taurus brakes were notorious for "warping". Dad's went through FIVE sets of rotors, all replaced at a well-known dealership in Dallas. "Must have gotten a bad batch of rotors" was their explanation. I thought that was a load of carp, so I took the fourth and fifth rotors, stuck 'em on a brake lathe and measured the run-out -- all four were under 0.001" (I have a good relationship with the shop foreman.) Next, I took all for and cleaned them up using garnet paper and reinstalled a pair and bedded the pads myself.

That was 6 years ago and they've been perfect ever since.

So, EVERY TIME you install new rotors, be extra careful to bed the pads correctly -- even if the mechanic/dealership says they've already bedded the pads -- you won't do any harm by bedding them in a second time.

Unfortunately, many ill-informed mechanics think that bedding the pads in is best done by braking very, very hard a few times and thats it. That's the WORST thing you can do to!!

If the pad manufacturer doesn't specify a bedding procedure, do this whenever you install a brand-new rotor, or whenever you change pad compounds:

Stop from 30mph to about 10 mph 3 times in quick succession, progressing from gentle braking to firm.

Repeat #1 from 45mph to 20 or so

Repeat #1 from 60mph down to 30, starting with moderate braking progressing to firm.

Repeat #1 from 70mph down to about 30 starting with firm braking. The third stop should be at maximum deceleration, keeping just short of engaging ABS.

Drive with minimal brake usage, allowing the brakes to cool off.

Chances are at some point along the way, the brakes will start to smell -- that's perfectly OK. Your brakes are getting hot and driving off volatile compounds from the brake pads. This actually will improve the pad's fade-resistance.

If you're using street pads, At some point during the procedure, you'll loose braking effort (i.e you'll fade the brakes.) That's fine (and pretty typical.) Once the brakes fade, go to step #5, even if you didn't make it to 70.

The idea is to gradually raise the temperature of the pads and rotor to a maximum temperature and then let it cool down completely. Pad material is transferred gradually during the heating process, and the cool off time is needed to give the pad material to fully bond to the cast iron surface.

Another case in point: I burned up a set of front pads on my race car in-between races one weekend. I only had an hour to change pads on the car and get out to the next race, and I didn't have another set of pads. I bought a set from a fellow racer that were a different compound and from a different manufacturer.

Since I couldn't get onto the track to bed the pads, and I had to make the next race, I ran the new pads with no bedding, ad minimal bedding on the race's warm-up lap.

The brake were FINE for that race, and the two races the next day. However, the next race weekend, the brakes got progressively worse. It got so bad that holding the steering wheel was difficult, and the car was darting all over the place under hard braking.

I pulled the rotor, thinking with such severe vibration, surely they were warped. Nope -- pad deposits again. A quick re-surfacing and proper re-bedding fixed things right up and I've been running those rotors and the same compound pas for the last year and a half with absolutely no issues at all.

This has turned out to be a lot longer than I intended. If you're really interested in this stuff, StopTech has an excellent white paper on the warped rotor myth, written by Carroll Smith, and well-respected race car mechanic who's campaigned cars at every level of motorsport including Formula One

en nog een artikel waarin omschreven staat waarom je je rem moet lossen bij stilstand...dat wisten we al, het mechanisme er achter is echter anders.

http://www.examiner....ed-brake-rotors

en

http://www.stoptech.com/technical-support/technical-white-papers/-warped-brake-disc-and-other-myths

December 13, 2011 bewerkt door ruudvd