Brake proportioning valve in the Turbo S
03-08-2002, 12:00 PM
#31
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REPOST - i jst found a 5/18 valve in one of the many parts i got from an auction, but anyway could i use this in my system for what i've decribed above. i dont want the tail to come out when stopping,i have the stock single piston(floating)calipers on all 4.
03-08-2002, 12:41 PM
#32
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Instigator,
I believe the bias valve you have is already a 5/18- if not, you would need to find out what it is first, but even the turbo's had the 5/18, which is why I'm going to the more agressive 5/33, to get more pressure to the rears w/out going overboard- I think a 5/45 or 5/55 would be too much for the 951. The 5/45 and 5/55 were made for 911's, that have a better weight distribution under braking, since they start w/almost 65% of their weight on their rear wheels at rest. Your car should be somewhere in the 49/51 to 50/50 area, whereas a 951 is in the 50/50 to 51/49 range. And while weight distribution is just ONE of the factors in the bias valve question, I hardly think a 5/18 would cause the rears to lock prematurely in any of our cars. Actually, I wasn't aware that ANY of the 924/944/968 series had anything BUT the 5/18 until reading one of the replies to this thread that said the 944S had the 5/33(?)- if that is the case, then it's likely that a regular 944 would be able to use a 5/33 as well, although I'd have to know all of the details to say for sure....
I believe the bias valve you have is already a 5/18- if not, you would need to find out what it is first, but even the turbo's had the 5/18, which is why I'm going to the more agressive 5/33, to get more pressure to the rears w/out going overboard- I think a 5/45 or 5/55 would be too much for the 951. The 5/45 and 5/55 were made for 911's, that have a better weight distribution under braking, since they start w/almost 65% of their weight on their rear wheels at rest. Your car should be somewhere in the 49/51 to 50/50 area, whereas a 951 is in the 50/50 to 51/49 range. And while weight distribution is just ONE of the factors in the bias valve question, I hardly think a 5/18 would cause the rears to lock prematurely in any of our cars. Actually, I wasn't aware that ANY of the 924/944/968 series had anything BUT the 5/18 until reading one of the replies to this thread that said the 944S had the 5/33(?)- if that is the case, then it's likely that a regular 944 would be able to use a 5/33 as well, although I'd have to know all of the details to say for sure....
03-08-2002, 07:25 PM
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[quote]Originally posted by instigator:
<strong>my doesnt have a proportioning on the MC, i was asking if puting the 5/18 would be advantageous for me now that i have bigger tire for the rear?</strong><hr></blockquote>Installing the valve will give you less rear braking. Since you've installed larger tires, you shouldn't have to limit the fluid pressure to the rear circuit unless you are experiencing lockup.
The brake proportioning valve works by changing the slope of the force curve. Below 18 bar (or 33, 45, or 55), whatever pressure is in the circuit gets applied to the rear brakes... 100 psi in, 100 psi out. Once you hit the cutover point, increasing the input pressure results in less of an increase in output pressure, so for instance, maybe you get something like 400 psi in, 250 psi out.
<strong>my doesnt have a proportioning on the MC, i was asking if puting the 5/18 would be advantageous for me now that i have bigger tire for the rear?</strong><hr></blockquote>Installing the valve will give you less rear braking. Since you've installed larger tires, you shouldn't have to limit the fluid pressure to the rear circuit unless you are experiencing lockup.
The brake proportioning valve works by changing the slope of the force curve. Below 18 bar (or 33, 45, or 55), whatever pressure is in the circuit gets applied to the rear brakes... 100 psi in, 100 psi out. Once you hit the cutover point, increasing the input pressure results in less of an increase in output pressure, so for instance, maybe you get something like 400 psi in, 250 psi out.
