[240] Interesting brake deal

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clay - 12 May 2007 10:11 GMT

Master cylinder went out on my '83 245 so I figured as long as I had to
visit all four corners to bleed the brakes, I might as well replace the
pads.
I discover they were only half worn but one was squeaking, chattering,
moaning, and generally annoying me.
Pedal had some pulsing and things shook like the rotors were warped.
Being the tightwad I am, I usually don't turn rotors... figure the
grooves just add area to them and make for better cooling.
I knocked the glaze off the rotors with some 80 grit, put new pucks in,
bled them and went for a drive.
Surprise, surprise! no more chatter, pulsing, "warped rotor" shaking.
Apparently, 'warped rotors' really aren't warped at all. It's the shiny
spots on the rotors causing all the shaking.
Something to keep in mind, next time the shop charges you for turning
the rotors because they're 'warped'.
ymmv.

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Michael Pardee - 12 May 2007 14:42 GMT

> Master cylinder went out on my '83 245 so I figured as long as I had to
> visit all four corners to bleed the brakes, I might as well replace the
[quoted text clipped - 12 lines]
> rotors because they're 'warped'.
> ymmv.

For all the grief pulsating brakes have caused, there is still a lot of
controversy over the cause(s). Some point out that "warping" per se doesn't
affect the brakes, that thickness variations are the concern. Others point
to cementite (http://en.wikipedia.org/wiki/Cementite) formation, and I think
there is a good case for cementite being a trigger for progressive
deterioration of the disc surface:
http://www.powerbrake.co.za/downloads/tech_01_judder.pdf It could be that
you broke a beginning cycle of disc surface trouble, maybe like the effect
that causes cars to create washboard surfaces on dirt roads.

Personally, I found I had much less trouble with pulsation after I started
using a torque wrench on lug nuts. YMMV.

Mike

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