Date:         Sat, 27 Mar 2010 15:12:41 -0700
Reply-To:     neil n <musomuso@GMAIL.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         neil n <musomuso@GMAIL.COM>
Subject:      Re: Brake Proportioning Valve: Traps Air?
Comments: To: Don Hanson <dhanson928@gmail.com>
In-Reply-To:  <6bc66ccf1003271316t55656842n3756ebb976142919@mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1

On Sat, Mar 27, 2010 at 1:16 PM, Don Hanson <dhanson928@gmail.com> wrote:
>   Dunno about a bleeder screw on the proportioning valve.but the
> Proportioning valve is probably why your rear brakes bleed fluid more slowly
> than the fronts.  The P valve is essentially a gate-valve that controls the
> flow of your hydraulic fluid..restricting some flow towards the rear,
> increasing the relative initial "action" of the front brakes.  Eventually
> you will have even pressure at all the wheel cylinders, but that P valve's
> function is to regulate or adjust how quickly the pressure can equalize...
>
>   If you had no proportioning valve...as you stepped on the brakes you would
> likely get rear wheel lockup.  You would have a 50:50 application of braking
> force, front to rear, with no valve,   but when you apply the brakes the
> vehicle weight shifts onto the front wheels.  So, the P-valve starts the
> braking at the front wheels and then, depending on the valve, lets  brake
> force take hold at the rear wheels more slowly.
>


Ah you say my other post.   ;)

My understanding is that the ball and spring inside valve are not in
use until one is braking hard. So..... does the act of pushing fluid
through when flushing or bleeding push the ball forward a a bit thus
reducing flow? Or does part of the valve design (ball, passages, etc)
restrict flow?

And to be clear to others, the BPV with bleeder I refer to, was seen
in my T2 Haynes manual. AFAIK, there weren't any installed on the
Vanagon brake proportioning valve.

Neil.

-- 
Neil Nicholson '81 VanaJetta 2.0 "Jaco"

http://tubaneil.googlepages.com/

http://groups.google.com/group/vanagons-with-vw-inline-4-cylinder-gas-engines