I understand what they do more or less and when I bought my car it had a tilton proportioning valve but it didn't work.

I'm installing a new one this week and will be on track in about a week. Anyone have any practical experience? I think I'll probably just set it or try to set it the same way my broken valve is now set. It looks like rain next weekend on track so I'm thinking in theory I'd like a little rear bias.

Any thoughts?

I change mine every different track and especially when it rains

Get 1-2 guys to stand beside (each side) of the path as you drive be down a paved surface and lock a wheel. Set your fronts to lock first button increase the rear until they lock and back up a hair

Of course the track at speed is slightly different... but you will be close and can tweek from baseline

Is the proportioning valve in your front or rear brake circuit? What calipers do you have?

The stock 914 brake prop valve is in the rear circuit of course, but depending on which calipers you are using, it sometimes makes more sense to put the valve in the front circuit (stock brake setups are usually more front-biased purposely to avoid ever getting rear wheel lockup).

Scott

I've used mine to dial in the front/rear balance just as Brant described; adjust it until rears just lock then back it down. I'm using it on an autocross car where the track doesn't change that dramatically so I only need to make adjustments to account for wet or dry conditions.

Valve is on the rear brake circuit. Currently running 930 turbo brakes but also have a set of S brakes that I may put on at a later date.

My 914 has one as well, but it's fully open nearly all the time. A former mechanic actually suggested removing it at one point since the brakes/car so are well-balanced in typical conditions. I really just kept it in case of rain/damp surface so I can dial-back the rears a tad. Also in theory at least, major changes in aero, tire wear or fuel load/weight could make enough difference to warrant fine-tuning, but in practice I just leave it untouched most of the time.

I suspect mine will be full open as well which I guess means if I close it at all it give me more front bias since it is in the rear circuit?

It really depends on what brakes and pads your running if you need it. I have a "T" in my car and could use more rear bias:

911M fronts with Hawk HP+
914 rears with R-4S

Car stops FAST, but locks the fronts pretty easy even with DOT-R tires.

Correct - you only can limit rear brake with your setup. Sounds like whoever set up your brake system mimicked the factory setup (prop valve in the rear circuit), which may not be an ideal setup with 930 brakes. I don't think the factory put a limiter or prop valve in the rear circuit of the 930, which means they handled the front-rear bias with caliper piston sizes. Assuming you have 930 fronts on the front of your car and 930 rears on the rear, I assume you'll need to run whatever proportioning valve you have in the rear circuit wide open, or remove it.

rear engine versus mid engine is the reason for the factory self regulating valve

The best method of balancing F/R bias is with a balance bar - more effective since the hydraulic in-line proportioning valve is very limited in the amount of adjustment. I tune the balance in gross with the pedal and fine tune on track with the hydraulic unit.

Tony

Balance bar with dual MC's is much better for gross adjustments. With an OEM-style double MC you are forces to have the same travel on both sides since the pistons are "linked," severely limiting your overall adjustability.

Just got through racing with my local vintage club. When it was dry I had it slightly closed but I'm not sure I really needed any front bias, I was just feeling it out. Spent a lot of time in the rain and ran it full open.

It was a great weekend. In the wet I destroyed the big bore cars.