proportional valve: how important to have working one?

[Phil Payne]

> yes... on the 2wd cars, the valve is down by the rear axle and
> presumably alters it's effect slightly depending on how much "pull"
> there is on a spring going to it.

I think ABS is the deciding factor rather than FWD vs AWD.

> On quattros, which don't have a dual diagonal braking system, the prop
> valve is under the master and is set to a fixed ratio.

I'm not sure the ratio is fixed.  I think there's a mass inside that is affected by
decelleration.

> The main function is to "proportion" the front and rear braking
> pressure, I guess the rears do not require as much since there is less
> weight back there, especially when the car noses down during braking.
> Some people bypass them when they go bad - I would worry about the rears
> locking up in a hard stop, perhaps making control of the car less
> predictable.

Agreed.

--
  Phil Payne
  http://www.isham-research.com/quattro
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