Do you know of engineering papers for what people call brake rotor 'warp'?

As far as I know there is no such thing; excluding cracks or other "damage" they pass/fail based on overall thickness. -----

- gpsman

Reply to
gpsman
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Joe Mastroianni wrote in news:kftfs3$rem$ snipped-for-privacy@dont-email.me:

None of the fairly-extensive Honda documentation I have gives any such number. Neither does any of my other documentation specify a figure. Sometimes it's advised to grind or replace the disc if grooving is "excessive", but then there is no indication of what counts as excessive".

However, I see universal directives to replace the disc if it measures below the wear-limit at the thinnest point measured on inspection.

Reply to
Tegger

Yeah, don't bother to respond to me if you can't even understand what the s ubject is. You're talking about brake runout but I'm not talking about that . What I'm talking about, dude, is the transference of pad material onto th e surface of the cast iron surface of the rotor. This layer is invisible to the naked eye and you can't measure it as runout because the whole idea of seating new pads is to get an even layer of this stuff onto the surface of the rotor. I'm not interested in getting sucked into your discussion about warped brakes and disk runout - dude.

P.S., If you think that machining a rotor results in a grooved surface... w ell that just explains everything.

Reply to
dsi1

The dirty little secret is that a lot of people will install new pads on a rotor that's grooved. I've done it myself and it seemed to work OK - but yo u didn't hear me say it...

Reply to
dsi1

where do you get this stuff? seriously, i'm fascinated.

indeed it does - but not he way you think. any machining operation leaves physical evidence, be it lathe or mill, and if you look under a microscope, you'll see it plainly.

which brings us neatly back to your obsession with deposition - what exactly is the effect you think it's supposed to have?

Reply to
jim beam

dude, /all/ rotors are grooved, even new ones. the question is, how big those grooves are relative to the abrasives in the brake pad, and what is their orientation.

Reply to
jim beam

Thanks for checking.

Googling for random manufacturer's specifications, I find this GM spec:

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Which says: Do not resurface rotors for light grooving. Resurface rotors only when grooves of 1.5 mm (0.060 in) or deeper are present.

"A dime may be used to determine disc brake groove depth. Place a dime in the groove, with Roosevelt's head toward the groove. If the dime goes into the groove beyond the top of his head, the groove exceeds 1.5 mm (0.060 in) and the rotor should be serviced. In Canada, if any portion of the letters of "Canada" are covered, the rotor should be serviced. If the groove is too narrow for the dime to be inserted, it is not a cause for concern."

Conversely this spec:

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Says: "Check disc for scoring or grooves over .012" depth. If either applies, resurfacing or replacement is required."

But, the point is that grooves have to be "really big" to fail a rotor.

PS: How did we get onto the side topic of rotor scoring anyway?

Reply to
Joe Mastroianni

rotor that's grooved. I've done it myself and it seemed to work OK - but you didn't hear me say it...

I don't bother keeping it a secret. I just buy pads when I do the fronts, then decide about the rotors when I pull the calipers. I've learned that if the rotors are "wavy" enough to feel it, there's a better chance for grit to get in before the pads wear in. The shallow wavy grooving is probably due to a hardness inconsistency in the rotor or pad. I've had wavy rotors get deeply grooved after putting new pads in. Then they will wear the pads real fast. Still not worth putting new rotors in if you're going to junk the car soon. If I know I'll have the car for more than a couple years I replace wavy rotors.

Reply to
Vic Smith

Since it's usually circular scoring, I'm "guessing" it's the particles in the pad - as the rotors should be relatively uniform (as compared to the uniformity of the pads).

BTW, for PAD IMPRINTS ... would just rubbing with 120 grit sandpaper remove the pad deposition?

Reply to
Joe Mastroianni

"Thread drift". More common than not. -----

- gpsman

Reply to
gpsman

I had a 1979 Plymouth Champ Twin-Stik I bought new. With about 5K miles on it, I took it on a hairball trip through the Sierras. By the end of the trip, the rotors were definitely warped. The dealer didn't have the special tool that car needed to remove the rotors, no one had needed it yet. So given the choice of waiting several weeks for one to be shipped from Japan, or machining their own tool, they made their own tool. At least, that's what they told me, and I can't imagine them making up stories to make more problems, work and expense for themselves.

Man, that was a little pocket rocket, before the term was invented. And I thought that coming from a '63 Vette.

Thanks for the judder links, Joe.

jg

Reply to
jgar the jorrible

rotor that's grooved. I've done it myself and it seemed to work OK - but you didn't hear me say it...

This sounds reasonable to me although professional mechanics probably don't have that option due to liability concerns.

Reply to
dsi1

rotor that's grooved. I've done it myself and it seemed to work OK - but you didn't hear me say it...

pad not the rotor - the chances of the rotor having circumferential bands of different hardness material are pretty much zero.

some pads are total garbage. these days, i'll only use ceramics because they're highly fade resistant and don't screw up the disk too much as they wear.

there are two reasons to replace [or skim] "wavy" rotors:

  1. if one is worse than the other, braking can become uneven causing the steering to pull to one side, particularly in emergency braking. [it can also make normal brake use somewhat non-linear too.]
  2. a new flat pad on a wavy disk doesn't have much contact area until the two are worn to fit each other. depending on the pad, that may take a few hundred miles of impaired braking. maybe not a problem if you're pottering about in some backwater, but definitely not recommended for city driving or freeways. if the pads are hard and the grooving deep, you can quickly get extreme local heating where the peaks of the groove touch the pad, and fade can become a real problem real fast.

regardless of how long the car is intended to last, if you [or you and your passengers] are planning on outliving that vehicle, it's wise to just replace the disks. even cheapo chinese $15 disks can be better than badly uneven oem disks with almost no pad contact.

if you want to avoid these problems in the first place, buy decent pads. depending on who the manufacturer is, oem is not always best. good modern pads, such as high quality ceramics, wear well, keep the disk in decent [reusable] condition, etc., as above. it's better to spend a couple of bucks extra on good pads and save on disk replacement later than it is to buy cheap pads today and have to replace disks and pads tomorrow.

Reply to
jim beam

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