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Re: emergency brake, for disc brakes. ( was: [T3] Stainless steel braided brake lines )

--- John Fessenden fess <fess-vwtype3.org@fess.org>
> however advice from this list was also that
> the rear disc brake kits were useless, since
> they were no longer balanced with the front brake
> you would lock up the rears and get less overall
> braking.

I should note that discs are not inherently "more
powerful" than drums.  They have a number of
advantages, including easier servicing, less
likelyhood of fade, and not as much of a problem with
water splashes.  Sheer braking power, however, can be
quite high for a good drum setup, until fade enters
the picture.

Brake balance is something of a tricky subject, and I
don't want to write a whole treatise here on the
subject.  However, brake proportioning valves operate
by reducing the amount of pressure available one pair
of brakes (usually the rear) to get the right
front/rear balance, so having rear brakes that are too
powerful is actually *required* for a proportioning
valve to work.  There are a number of adjustable
proportioning valves available for fairly reasonable

You actually want the front brakes to lock first in
any actual situation.  In a straight line, it doesn't
matter all that much, but braking in a corner with the
rears locked means you spin pretty much instantly. 
With the fronts locked you simply understeer straight
on, which is easier to cope with in most situations.  

This is something of a problem for many cars, and esp.
cars with relatively high centers of mass, as the
weight transfers forward under braking, giving more
traction to the front wheels and less to the rears, so
the harder you brake, the less rear braking force you
want.  Some cars have employed dynamic proportioning
valves to handle this, sometimes very simply.  Many
FIATs with solid rear axles had a lever arrangement
with a link to the prop valve attached to the body
above the axle.  When the body rose away from the axle
(as it will under braking), the prop valve reduced the
rear brake power.  The more the body rose, the less
rear braking power there was.  One could do a similar
thing on a T3 by attaching the link to the rear spring

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