Re: Re: RE: Rear brake conversion

From: Michael Maskalans (dml@tepidcola.com)
Date: Sat May 01 2004 - 10:07:50 EDT


On May 1, 2004, at 09:03, Bill Knight wrote:

> If disc brakes are so good then why do all tractor/trailer rigs have
> drum
> brakes?

because they're cheaper. discs are more complex and more expensive,
and generally not quite as stupid-simple-reliable (how many times have
you seen a caliper lock up? how many times have you seen slide pins
strip out? on the other hand, how many leaking wheel cylinders have you
seen in a drum continue to work fine until they're found and replaced?)

> If drum brakes faded so much and did not have such great
> stopping power I'd stay away from the front of those big trucks.

you should stay away from the front of big trucks. and they do fade
like a sonofabitch - those runaway truck ramps aren't there for looks -
if a big rig comes downhill too fast, drums hold heat incredibly well,
and the hotter they are the less stopping power you have. In the days
before compression brakes, those ramps got a lot more use than they do
now.

as materials heat, they expand, and whereas that would push a disc into
the pads harder, on a drum increases in size and runs away from the
shoes.

there's a reason the first application of discs was airplanes - when
you need to haul yourself down from high speed, you need to be able to
shed heat, and drums can't begin to compare with discs in ability to
loose heat.

> They have
> drums all the way around. And how many times have you seen someone
> pull in
> front and cut thes trucks off andwhen they hit the brakes tires smoke
> because the brakes work.

often you'll see and smell a lot of brake smoke in those situations too
- anything is capable of locking a tire up. but to modulate from
lockup (it's right before lockup that you're stopping the hardest) and
to keep fade at bay is far more difficult. I can lock up the tire on
my bike - does that mean it's as good a braking system as my dakota
has? Hell, I don't remember anything stopping a tire from turning
quite as effectively as the coaster brakes on my first bike.... how's
that for your next truck?

> For a smaller vehicle application disc does make
> sense but I would not go so far as to say disc brakes are superior to
> drum
> brakes.
> Let the flames begin.

you're wrong, but that's okay: you're not designing cars or big rigs....

look at racecars - $$ mean nothing, and performance and weight do:
discs. look at airplanes - $$ mean nothing, and performance and weight
do: discs. look at big trucks - bottom line and reduced maintenance
are key, weight is nearly meaningless: drums. look at upmarket autos -
$$ and performance both matter: discs. look econoboxes - $$ means a
lot, and safety is the next concern: balance $$ with safety/stopping
power with disc/drum setups.

--
Mike Maskalans            <http://mike.tepidcola.com/dodge/>
84 RamCharger 360 (parked)         98 Dakota CC 318 (Fixed!)
mobile.612.618.4652   campus.585.274.2246   fax.360.364.3930



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