Exploding Rotors: why you do not drill

[Brett Dikeman]

I just got back from working a club event at Lime Rock- a little wet
yesterday, little on the hot side today(in both cases, for workers),
but as usual a rewarding experience.  Certainly kept busy, save this
afternoon when I took a ride with an instructor every chance I could
get(incidentally, thanks to Carter, who gave the fastest ride of the
set.)

One of the things I help out with is tech'ing cars. It's not exactly
mind-taxing work, nor do you need strong mechanical skills- you're
checking over a dozen plus simple things, to basically make sure
nothing has happened to the car since the student had a pre-tech done
by a certified mechanic(which is at least 2 dozen lines long, and is
required- if you don't have it done, you don't run.)  Is anything
leaking, is the suspension about to fall off, battery bouncing
around, brake fluid 1+ year old, any caps about to come off, yadda
yadda.

So the night before, when we open tech for a couple of hours, up
pulls a TT.  I start going down the checklist, talking with the
student...and get to the wheels/tires/brakes part.  I explained to
the student my personal feelings about cross-drilled rotors, and the
student said something about just wanting to give 'em a try, etc...

Fast forward to today- day #2 of the event.  I'm riding with a
friend/instructor in his UrQ, and after a few laps, we get a yellow
at the Uphill station.  Mike comments on what he thinks are chunks of
rubber on the track- and as we zip by- there's a blue TT sitting off
on the right in the chicane, with the driver+passenger on the hill
waiting for the end of the session.  Mike has some trouble with the
UrQ, so we pack it in a lap or two later, and I resume working the
pit lane for the rest of the session.  In comes the rungroup, and
then- at the tail end, very slowly, the TT on the spare tire.
Thusfar, it looks like he's had a blowout.

Not quite.  The carnage:

-rotor exploded into about at least a half dozen chunks.  All chunks
had fairly clean breaks centered on the centers of the holes.

-the entire caliper was ripped off the car.  One guide pin mount
gone, other intact- guide pin probably sheared.  Pads nowhere to be
found.  Outer bracket, nowhere to be found, only the piston half was
recovered- and it looked like it had been in a cement mixer with some
boulders.  Bleeder nipple and brake hose fitting were unrecognizable.

-the rim disintegrated.  There's no better word for what happened.
Almost the entire inner area was broken into dozens of various sized
chunks- only the spokes were intact.

-the tire had at least one large puncture in the middle of the tread

-brake line obviously severed

Damage was rather well-contained; the wheel well liner was only
lightly cut in a few places and there was zero damage to the
body/paint- with all that metal flying around, kind of amazing.

Thankfully, the failure was on the right front, not left front- if it
had been the left front, it could have put him head-on into some
armco.  It would have been a very ugly collision.  Instead, the right
wheel failure probably pulled him into the turn, and saved his bacon.

Pictures of the carnage:

http://frank.mercea.net/~brett/pics/car/rotor_carnage/

Of particular note are the pictures of the left rotor- I saw at least
two cracks, which I took photos of.  They were deep in places, and
extended almost the entire width of the rotor surface.


Brett
--
----
"They that give up essential liberty to obtain temporary
safety deserve neither liberty nor safety." - Ben Franklin
http://www.users.cloud9.net/~brett/