Like most of our cars, the brake proportioning valve is 45 to 50 years old. While it's design and action is relatively simple, - holds the hydraulic pressure at a factory determined maximum value (550lb/square inch?) while under pedal pressure, the probabilities of function failure must exist - whether through wear or contamination.

In my case, my brakes work well and when bleeding them all four calipers appear to experience free flowing brake fluid. My proportioning valve does not leak and there are no signs of abuse, or that it has ever been "serviced", but the latter is hard to tell. My guess is it still works or is "seized" and works as a simple T connection for the three brake lines.

I have refurbished stock rear brakes and have just installed Boxter front calipers on 911 Carrera suspension. Brakes are much improved and I can't get the rear brakes to slide under hard braking, suggesting the more effective front brakes "overpower" the rear brakes such that a proportioning valve is no longer necessary.

Any comments will be welcome.

I bet @Eric_Shea could answer that question.

Keith, if it turns out you need the proportioning valve pm me. I have a few sitting around.

This suggests the proportioning valve is working.

You still need a rear proportioning valve. If you were getting full pressure to the rear (without a proportioning valve) you would get rear wheel lock and especially so on wet pavement, snow, or ice.

You never want rear wheels to lock 1st. It makes the vehicle inherently unstable.

I highly recommend Eric's services. You want and need a functional proportioning valve. His price is incredibly resonable and ensures that the 40-50 year valve is working properly.

Watch your terminology.
It's known as a 'brake pressure regulator'
I was recently corrected by Mr. Shea himself.

PMB rebuilt mine and it came back looking like new of course.

Thanks for your responses. After more testing will post again.

Don't disagree. You are correct. It is the equivalent of everyone calling anti-roll bars -- sway bars. I certainly don't way sway!

All three of our 914’s have full PMB restored braking systems and new master cylinders The only problem is that they look so good it forces us to powder-coat the backing plates and plate the hardware