Michael D. Porter wrote...
> I'm wondering about how you measured the run-out on these. You say you
found low spots--was that done by miking the
> thickness around the rotor, or did you see low and high spots with a dial
indicator while the rotors were mounted?
Both, but again, I saw maybe a few tenths - not thousandths at all. Wheel
bearing play makes it hard to believe that anything less than a few
thousandths is real.
> If the former, it could be that the rotors are getting too hot and
developing work-hardened spots. When that occurs, the
> hard spots don't wear as quickly as the rest of the rotor, and gradually,
the non-hardened areas around them will wear,
> creating a ripple as the pad moves over the surface.
That's been my assumption every time I've had bad rotors since my first
experience with pulsation, on my 1978 Turbo LeSabre at 27,000 miles. Cut
the rotors and put in new pads and drove maybe 60,000 miles till the pads
wore out with no more trouble.
> If the latter, the rotors may be warped by too much heat. Every once in a
while, a manufacturer will put out a big batch
> of bad rotors, so every replacement rotor is just as bad as the one
before. In the early `70s, I bought my only new car,
> a Mercury Capri, and it was in the shop nine times in fourteen months for
brake rotor warpage. Probably had three sets
> of new rotors installed (they would cut them a couple of times, until they
hit the limit, then install new rotors on my
> next visit). Didn't make a difference--each new rotor was from the same
batch as was on the car originally. If the pads
> you're using are producing a bit more heat than the stock pads, that might
be enough to warp them.
But, like the guy who wrote the article Steven Trovato posted, I've NEVER
seen a warped disk, probably due to my avoidance of certain kinds of cars.
When manufacturers started putting disk brakes on cheap cars, they skimped
and legions of Hondas, etc. had warped disks every time they hit a puddle.
I don't really hear about that any more - but then again most Hondas,
Toyotas, etc. never break or wear out. Funny how my two Japanese cars were
so far from that standard.
> As a test, with a fresh set of rotors, I would bite the bullet and buy
factory replacements from the dealer, rather than
> use an aftermarket brand. If the problem persists with those pads, you can
be fairly certain that the fault is with the
> rotors.
That may be what I do with the Suburban's rotors, but I'll try GM-rebuilt
calipers with GM pads on these rotors (resurfaced) first. Calipers are
original and I just can't believe I've got almost 200,000 miles without
problems. Time to rebuild them just because, and since AC-Delco rebuilt
calipers are reasonably cheap and come with all new hardware, preloaded GM
pads, etc. - I think I'll go that way.
Karl
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