I have an epidemic of disk brake pulsation, with 2 different cars doing it
soon after brake jobs. Multiple times in a row. I've been doing this a while
- starting in 1965, on my '57 smallmouth TR3. I'm not a full-time mechanic
but I think I know most of the important stuff. My race cars never did this,
and neither did any of the dozens of other disk brake jobs I've done over the
decades. Now I'm stumped.
Our '93 Suburban kept its original rotors till about 170,000 miles. Though
they were actually worn below the service limit when we bought the vehicle (at
80,000 miles) the rotors were true and never pulsed, so I just kept putting in
new pads, going through maybe 4 sets of Raybestos Brute Stop
lifetime-warrantee pads. Great stopping power, but each set wore out in 15 -
20K miles. Had them on another car and got about the same mileage, and
Raybestos apparently knew about it too. Eventually they told me I'd received
my last warrantee replacement set and so I switched to their (then new
top-of-the-line) Quiet Stop pads. Those have lasted well, but not long after
I put them in the old faithful rotors developed a pulsation. I put in new
Raybestos premium-grade rotors, cleaning them well before installation.
Pretty soon (a few months) the brakes started pulsing again. Within the
one-year warrantee I got 2 more replacement pairs of rotors for the same
problem. They would be fine when new, but after a month or two they would
start to pulse and when I miked them they'd show measurable low spots. I'd
take them back and get a new set under warrantee. Now the warrantee is many
months past and I'm sick of doing brakes a few times a year on the Suburban.
The pads are finally about worn out, after maybe 40,000 miles.
Switch to my '94 Mustang GT.
I bought it with 74,000 miles and it developed a pulsation within the first
year, so I ordered a set of Brembo rotors and EBC Greenstuff pads, wanting
some really great brakes. The Brembo rotors, BTW, are actually US castings
from American Bridge and Iron. Beautiful pieces to look at. The
highly-ballyhooed Greenstuff pads were never a religious experience, and in
fact I bet whatever I would have bought cheap at NAPA would have been better.
Anyway, the worst disappointment was that I soon felt a pulsation with the new
rotors and pads - a couple of months at most. No real measurable runout, or
thickness variance when I checked the rotors - maybe a tenth or two, maybe my
imagination. Tire Rack (where I bought the rotors and pads) told me they'd
heard something about this before, and it was some sort of contamination on
the rotors generated by the pads. They said to try to re-scuff the rotors.
That didn't help. I've tried hard stops to maybe burn off whatever is there,
but the pads begin to fade and stink with the first hard stop. And still
pulse afterwards.
I'm pretty religious about making sure all caliper hardware is unrusted,
clean, and greased, and the rotors are clean before I put the pads on. I wipe
off any errant grease again before putting on the wheels. I always apply the
anti-squeal goop that comes with the pads (or else CRC's stuff) and let it dry
properly. I've never tightened wheels with an impact ever, but now I've even
taken to torquing wheels rather than relying on my calibrated hands on the
cross wrench. Much of this is stuff that lots of people ignore and they still
don't usually have problems.
Obviously I have to start over again with new brakes on both cars, but I want
this time to be the last for a while. FWIW, I think the Quiet Stops are
ceramic, and the EBC Greenstuff are Kevlar. Both are destined for my garbage
can.
Suggestions?
Thanks!
Karl Vacek
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