"jim beam" <spamvortex@bad.example.net> wrote in message
news:r5Wdnc1D2fOgUNjbnZ2dnUVZ_s2vnZ2d@speakeasy.ne t...
> Michael Pardee wrote:
>> I don't want to trigger another never-ending thread, but in research for
>> another forum I stumbled across this essay on brake pulsations at
>> http://www.powerbrake.co.za/download..._01_judder.pdf
>>
>> It seems to pull together the cementite issue with the issue of disc
>> thickness variation and supports it with pictures. I've seen the
>> individual pieces in various places but thought this did a good job of
>> making sense of it all. There is also a good treatment of brake pad
>> selection that mainly reinforces my preference for staying with OEM.
>>
>> Mike
> dude, the moment they start talking about cementite, and getting it wrong,
> they lose all credibility.
>
> bottom line, honda disk hubs are ultra-lightweight. they elastically
> distort when the lugs are tightened. if the torque is incorrect, the disk
> starts to sit out of plane, and the brake judders. it's real simple!
>
> metallurgical problems can exist, and they show disk cracking as one of
> them, [but get that explanation wrong too], but cementite transformation
> at normal braking temperatures is pure b.s.
>
> i've permanently fixed this issue several times now on different civics
> and most recently on my crx. simply apply a thin layer of antiseize to
> the hub surfaces, torque in a 2 or more stage process and bob's your
> mother's brother.
>
> i've been thinking about this for a while, but i guess this article
> ratchets things up my agenda - i must go to a junk yard and take some pics
> of things to look out for in the disk brake department. there's one thing
> particularly i want to show for cheap chinese disk castings.
>

In spite of your doubt about the role of cementite, did you read it all? And
do you have disagreements about the rules for avoiding pulsations on page 7?

I am a skeptic about cementite formation as a factor in brake disc
deterioration, but looking back on the odd visual patterns I've seen on some
brake discs after being in service a while I am not so skeptical. I'm sure
you've seen those, too - scaly looking areas with irregular shapes. Given
that cementite will form below 700 degrees C (according to the link) and
that braking under adverse conditions such as short downhill freeway
off-ramps dumps a whole lot of energy into the brakes in a hurry, it makes
sense. As the link points out, cementite isn't necessarily the root cause of
brake pulsation. It places heavy blame on poorly cleaned surfaces and
anything else that causes uneven friction. The disc with darkened areas over
the dividers in the cooling vanes (figure 4) really turned on the light bulb
for me. I've seen that.

I too have experienced much less brake trouble since I began torquing wheels
with a torque wrench. But the pulsations often still appear down the road -
just farther down the road. Something is happening to what were carefully
installed brakes, and not just on Hondas. My Volvo is even touchier.

Does this prove cementite is to blame for all cases of brake pulsation or
worsening pulsations? No, but it is a good fit in that the conditions to
create cementite are known to exist in heavily used brakes. It isn't proof,
but it sure is more credible than global warming theories. It has my
attention.

Mike