At 08:35 AM 7/4/2010 Sunday, Dave Mcneely wrote:
>Now, if drum brakes are less effective than disc brakes, why do so
>many vehicles have rear drums?  Vanagon content here in that
>vanagons are built that way.

Drum brakes were the standard automotive brake for many many years,
although my grandmother's Studebaker still used band brakes.  Some
time in the sixties IIRC disk brakes began to be available, and there
was discussion in the magazines like Motor Trend and Road & Track as
to whether the handling problems from increase in unsprung weight was
a greater disadvantage than any increase in brake performance would
make up for.

Clearly the universe decided otherwise, and AFAIK front drum brakes
have entirely disappeared (I wonder what the Trabant used?).  Early
systems were mostly dual-piston, with the caliper fixed in place; my
Saab 96 had a pivoting system where the pads started out very thick
on one side and were even when they were worn out.  More recently
single-piston designs with sliding calipers have been popular as
they're cheaper to build.

Until lately nobody considered putting disk brakes on rear wheels
because the rears do so little actual braking that it doesn't really
make sense -- you'd end up with more unsprung weight, which is bad,
with no particular advantage in braking, since the rear brakes in
general have to be restrained from using their full capacity anyway.

Disk brakes do have two advantages for rear brakes -- they are
inherently self-adjusting, and they look cool -- at least until they
get all rusty.  I'm waiting to see what happens when all these fancy
cars with transparent wheels start getting rusty disks and calipers;
will they look so pretty then?  The heat from braking accelerates corrosion...

But if you want my bet as to why cars are being built with rear disk
brakes (leaving aside race cars) -- I suspect it is purely cosmetic.

Yours,
David