Eric_Oz_S2

Since stiffening up the front and rear suspension and lowering all round, I am now getting significant front lock up under braking. The S2 has a 18/5 proportioning valve installed on the master cylinder. I have heard that 33/5 is a useful upgrade.

Would a 33/5 be "too much" for an S2. The S2 uses the same brakes as the turbo, but the Turbo S and later turbos have larger front pistons (36/44 vs 36/40).

Note that the car is predominantly for track use.

Anyone used a 33/5 in an S2 or early Turbo?

A variable proportioning valve may be a better bet, but it would then need to be professionally installed.

gt37vgt

i was under the impression that most people use that 33/5 for most set ups ..

Bri Bro

Changing the bias valve may not help this problem since the brakes setup hasn't changed. As you change suspension and ride height, the threshold of your braking will change since the balance of the car has changed. Have you tried to adjust your braking pattern to find your new threshold and how many driving hours do you have on the new setup? It took me some time figure out how to drive my car after changing out the stock suspension. The car drove very different near the limits.

Eric_Oz_S2

Brian,
The problem is the braking deceleration with the new setup is less than with the old suspension. I think another part of the problem is my pads are less efficient than they used to be (50% worn) and don't have the bite they once did. This means that because I have to apply more pressure to the pedal, in effect the rear gets less pressure (because of the bias valve cutting pressure above 18 bar) than it would with "grippier" pads (which would require less pressure).

Tried new PFC 97 in rear - braking feels stronger but then rear locks up first.

Eric

Bri Bro

If your using PFC 97 in the front, I would think you are getting good first bite out of the pads when they were new, at least I did. I found the pads to be a little hard on the rotors and I had to replace the rotors once or twice a year but they had great bite and had little fade with heat. I would NOT like to get too much rear braking,as that makes trail braking very hard to do.

After the pads get to 50%, they do start to go away and I retire them to the spare box. Maybe it is as simple as getting fresh pads on the front.

Changing the brake bias valve works well with big reds/blacks on the front and stock on the rear. I never needed it on a stock setup.

gt37vgt

well the valve will increase rear line pressure when system pressure goes above 5 bar ...it is a pretty common thing to do ..

Oddjob

If you use a 33 bar, instead of the stock 18, there will be an increase in the pressure to the rear brakes above 18 bar. The "5" is for 50% reduction.

When you say lockup - I am assuing you are hitting the ABS on an S2? Going stiffer with the suspension should have no negative impact on braking performance, typically it improves it. Did the alignment get changed radically when the new suspension was installed? How stiff did you go? Any work done on any of the brake system components at that time?

Pad wear usually does not decrease the pad coefficient of friction; they have less material and therefore heat up faster and will fade quicker. I have not used Perf Frict, but that is the case with other brands I have used like Pagid, Cool Carbon, Porterfield and Hawk.

When you stiffen up the suspension, the car dives less in transition. So under braking there is less weight transfer (nose dive) to the front. Therefore the rear does not lighten up as much, and you can get away with using more rear brake without impending lockup.

As I stated in your x-post on the 944 board - you can put the 33 bar valve on the car, and it will use more rear brake and slightly improve straight line braking performance. I have used higher rate rear proportioning valves on 4 of the 5 944s that I have tracked. Its a subtle improvement, dont expect a dramatic change in braking.

Yes, if you do a lot of heavy trail braking it might be too much rear bias when the car is rotating. But may still worth trying.