"Ashton Crusher" <demi@[EMAIL PROTECTED]
> wrote in message
news:oqp724hom34taqbtdaqbsd07fjh7jdea7f@[EMAIL PROTECTED]
>
> Is that how it works these days. In the old days they used a hold off
> valve to make sure the rear brakes came on before the fronts because
> it makes the car more stable to do it that way.
>
Your "hold off" valve was actually called a metering valve. This was
required on vehicles with a combination of front disc/rear drum brakes.
This
was to keep the front brakes from applying before the rears.... This was
accompl;ished by "metering" the amount of fluid sent to the front brakes -
limiting it, if you will, the movement of the front calipers until the
rear
drums "caught up". What it never did was to cause the rear brakes to apply
"first", rather, it's purpose was to have the brakes apply in unison.
Which
brings us to the pro****tioning valve....
The proprotioning valve was there to limit the pressure to the rear
brakes.
The harder we brake, the more weight is ****fted to the front wheels... If
we
allow the rear brakes to lock up early, the car will swap ends...
Notice we haven't mentioned the residual pressure valve.
Some vehicles used a "combination valve". This was a metering valve plus
pro****tioning valve combined into one unit. But the theory is still the
same
and it does not involve applying any one axles brakes "first". Something
like that is going to be a nightmare from a stability standpoint.
With the advent of 4WABs, all of these functions can be incor****ated into
the hydraulic control unit.
Misunderstanding both vehicle systems as well as vehicle dynamics can lead
to all kinds of problems... Things "these days" work the same as they did
"in the old days" as far as dynamics are concerned... Depending on the
system, technology may achieve these conditions in a mechanically
different
way...
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