OT: brake pressure regulator adjustment

I'm changing the rear drums on my Golf over to discs. I understand that the brake pressure regulator (same thing as a proprtioning valve??) needs to be adjusted as a result.

The Bentley manual says that this adjustment is a black art that should only be attempted by the VW gurus at the dealership. I'm not too crazy about that option because they usually pee their pants and cower in the corner when they see that my car is a little less than bone stock.

What I'm wondering is, if I had the numbers (i.e., the desired operating pressure) for my new calipers, and threaded a pressure gauge into the bleeder port hole, could I then have a buddy stomp on the brakes, read the pressure, and adjust the pressure regulator accordingly?

I've done a similar task to this on aircraft brakes, but there's different things to consider with automotive brakes and I want to be sure I'm addressing all the important issues.

Any thoughts would be appreciated.

[Bill Verburg]

One thing you need to do is be sure that the residual pressure valve on the rear circuit is removed. The best thing to do is follow the manufacturers suggestions as far as a p/v is concerned. If not try an adjustable p/v and tune to suit.

Do you mean like one of those cockpit-adjustable brake bias controllers that some race cars have? I suppose that would do it, and make all the ricers on my block soooo jealous.

Speaking of rice, do you know how hard it is to find rear disc conversion kits for compact cars that don't have drilled and gas slotted rotors?

I'll go looking for the residual pressure valve, too. Is that a part used specifically for drum brake installations?

Thanks for the reply. I hope some info might come up here that would be of use to anyone considering a brake upgrade, whether on a 911 or another car.

[89911]

You don't need to put the adjustments in the interior of the car. In fact, it is better in a remote place such as the front compartment to avoid accidentally changing the settings. Once the restriction is removed and replaced with an adjustable bias control, it is simply a matter of using some old tires and a nonpublic stoping area and doing full braking until lockup and adjusting the rear to lockup after the fronts. Helps to have a spotter outside the car to monitor the action.

[Tyson Schmidt]

Rob, the residual pressure valve is for drum brakes only, and if used on a disc brake set-up, it will not allow the rear brakes to fully retract.

Sometimes they are built into the master cylinder, or are a fitting on the master cylinder. Or at the junction box.
You might just consider buying a master cylinder for a 4 wheel disc brake car.

Yeah, the cockpit adjustable setup is a little over the top. I was half kidding when I said it, but the bling factor of a red anodised brake bias knob on the dash is undeniable.

Tyson, I was looking into master cylinders anyway, because I wonder if my stock one can move the volume required to operate four calipers instead of only two with the smaller drum brake pistons out back.

Master cylinder sizing is decided upon after considering all kinds of things, some of which kind of conflict with each other. Hopefully I can mimic some sort of factory setup that will work well.

If anyone can add to this thread with their experience in upgrading the brakes on their 911's, that would be great. The laws governing hydraulic systems operations still apply whether it's a 911, 727 or a go kart, so there might be something I can learn.

Plus it might keep this from being banished to the OT forum. Just read Wayne's post...oops. Sorry, man.