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Originally Posted by JFP in PA
Without actually checking, I really do not know, but I suspect they do. What I do know is that we have installed several two and four wheel up grades, and none of them required the proportioning valve to be changed (the kits all came from Porsche). I have also worked on a couple of early cars that did the four wheel upgrade the hard way (swapping out the rear carriers with units from the bone yard) and neither had changed the master cylinder or proportioning valve either.
What I can tell you is that from 97-04, there are only two master cylinders for these cars: with or without stability management systems (PSM). The base and S car carry the same master cylinder....................
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I'd be really surprised if they were the same. Brake balancing is dependent on brake torque at the front/rear and weight distribution, which is different between brake designs and car models. Considering all the little "tweaks" that they make between models in the suspension because of weight balance, I'd think they'd do the same with brake balance.
It's not that you can't get away with proportioning that's off somewhat, it's just that the brakes are not as effective as they could be. In fact, it might never even be noticed especially with ABS keeping premature lockup from showing.
Adding more braking torque to the front wheels (bigger brakes, higher friction pads) will tend to lock them up sooner. So the proportioning should be shifted slightly rearward. Normally, a car is set up to lock up the fronts before the backs anyway to maintain stability, so upgrading just the fronts w/o the proportioning wouldn't change the car's balance but it wouldn't optimize the setup either. Upgrading the rears without the fronts, or significantly more than the fronts is when you'd start to run into problems with early ABS activation and a loss of stopping power.