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Re: [T3] Brake Pedal Set Up

On 20 Mar 2006 at 19:36, andy wrote:

> > The reason is to ensure that there is enough movement possible for the pedal in
> > case one circuit fails, as the pedal then moves the full distance that circuit
> > allows before pressurising the other (hopefully OK) circuit.  You don't want it
> > to hit the bulkhead before it can do that.
> this doesnt make any sense to me. from my understanding....
> a dual circuit MC uses one circuit for the fronts and one for the rear.
> they are both always active. if you lose one you still have half of your
> brakes, unlike a single.

If you look at the cross section diagram of a tandem MC you will see 
that the pedal force is applied directly to the rear circuit. The 
pressure is then transferred hydraulically from the rear circuit to 
the front circuit. If there is a leak in either circuit, that circuit 
collapses. The amount of collapse is limited by the construction of 
the front and rear pistons, but the collapse still consumes 
significant pedal travel.

If the pushrod is incorrectly adjusted, it is possible to set things 
up so when one circuit fails you will run out of pedal travel before 
you get the remaining circuit to work.  

The available pedal stroke is almost never a problem as long as both 
circuits are working correctly; it's only when one circuit fails that 
it becomes important.

> the reason the mc needs to fully disengage is to allow the pressure
> release ports to open. otherwise there will always be pressure on the
> brakes, your mileage will suffer, they could overheat and they will wear
> out prematurely.

Exactly right.  ;-)

Jim Adney, jadney@vwtype3.org
Madison, Wisconsin, USA

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