911 SC brakes, 19mm MC combo question Options

[RoadGlue]

Hi everyone,

I've recently entered the world of bigger brakes, and hoped I could get some feedback here about proportioning valves. I have a set of 911 SC brakes ready to be mounted, and wondered if I'll get the correct brake bias by ditching the stock proportioning valve. I have the "T" fitting, but wonder if I shouldn't put an adjustable proportioning valve inline. Seems like it would always be better to have an adjustable proportioning valve, but is it absolutely necessary with that brake configuration?

Mmmm, brakes.

Thanks!

Randy

[lapuwali]

QUOTE (andys @ Apr 5 2005, 12:09 PM)

If there is a tested and established combination of parts known to work, then I suppose that would be ok. However, I see no way of obtaining proper or optimum brake balance without some from of adjustability built into a retrofit system (or perhaps swapping $$ parts until you reach good balance). Anyone with roadracing experience knows the value of this. (And) Yes you can have too much front brake.....A symptom of this becomes evident when under hard braking, the car feels like it wants to swap ends or becomes directionally unstable. Crank in some more rear brake, the car becomes stable on entry and you'll shorten up your braking distance. Too much, and of course you'll start locking the rears. BTW, the rear rotors on my Carrera brakes are slightly larger in diameter than the fronts (282mm F vs 290mm R). FWIW. Andy

Adjustability is indeed a good thing, but the point being made here is adding an adjustable prop valve will generally not give you any useful adjustability. With stock /4 rear calipers and SC front calipers, the valve would be wide open and still too front-biased. Thus, there's no way to get proper balance with a setup like that, no matter how much you spin the adjuster, and a T is just as good as an adjustable prop valve.

The only thing wrong with the stock 914/4 brakes is the calipers are heavy and the rotors are a bit undersized and not vented. Using most 911 calipers doesn't help the weight problem, and the non-vented rotors only seem to be a problem on the track. Using all stock (including the MC!) 914/4 parts with good pads, within everything in tip-top shape (rubber lines aren't swelled up, calipers aren't sticky, etc), I'd bet would be perfectly satisfactory for most people on the road. All too many people (including the DAPO with my car) have switched to 19mm MCs as an "upgrade", and now are hell-bent on adding bigger calipers, all to simply return the system back to the same hydraulic advantage it had with the stock MC.