ABS & Proportioning Valve Question

[Quiny]

I did not use the ABS from my 2002 donor but I did use the stock calipers, if you check my build thread you will see in one of the go-kart videos that the fronts do lock first with the proportioning valve wide open. I have since started to adjust it to even things out. Still fine tuning on every test. Keep in mind as well the adjustment is counter-intuitive (screw in vs. screw out).

[Oppenheimer]

It certainly seems like a better idea to even out the balance naturally, than to resort to reducing the front bias with proportioning valve(s). If its as simple as using another set of front calipers on the rear, so they are all 4 the same, that sounds like a pretty sweet solution (even if it involves some effort to make those calipers fit on the rear). I can understand FFR wanting to go with the prop valve though, to keep it single donor.

[Bob_n_Cincy]

It certainly seems like a better idea to even out the balance naturally, than to resort to reducing the front bias with proportioning valve(s). If its as simple as using another set of front calipers on the rear, so they are all 4 the same, that sounds like a pretty sweet solution (even if it involves some effort to make those calipers fit on the rear). I can understand FFR wanting to go with the prop valve though, to keep it single donor.

Oppenheimer
That is exactly what I did.
http://thefactoryfiveforum.com/showt...l=1#post173658
Bob

[C.Plavan]

I'm in the camp of do not change anything until you try the first solution. There are tons of 818S's running the stock proportion valve without going to bigger rear brakes. You want the fronts to lock up before the rears.

I could not get my Wilwoods to lock up with the pressure full front. I did not like the feeling at all at the track either. I just changed to a more aggressive pad, and now pedal pressure is perfect, and I can lock up the fronts out on my test loop easily with little pressure at the same valve setting. I will probably have to back out some front pressure next time at the track.


Just as a FYI-
Screw out (Counter Clockwise) all the way for maximum 57% reduction in stock pressure.
Screw in (Clockwise) to add more pressure to front brakes.

http://www.wilwood.com/PDF/DataSheets/ds488.pdf

[Scargo]

I got the same answer as what is being said and discussed here, from two brake experts. First, an engineer that used to work for AP and then Stoptech. I also was told that a proportioning valve will slow braking response and that a balanced system and adjustable bias on the master cylinders, using a racing pedal box, like the Tilton 600 and 900, is the best way to address braking pressure bias. I submitted all the pertinent data about my R to Stoptech and they said the weight distribution under braking is very close to 50/50, so I could use the same caliper sizing front and rear.
I went with, Front & Rear: STR40/28-32 (28 &32 are the piston sizes), 328x28mm rotor
Recommended Master Cylinder Size: Front: ¾”, Rear: ¾”
Recommended Pedal Ratio: 5.61
You can also juggle brake pads to get the best results.

[TouchStone]

Here is what I'm doing based on a suggestion from Wayne. I haven't tested it but it makes sense to me.

Rather than matching the original Subaru design of having the brakes paired (front left / rear right) and (front right / rear left), I will be pairing them (front left / front right) and (rear left / rear right). This allows a single proportioning valve on the input to the ABS module for the front pair, rather than two prop. values after the ABS module. Changing the wheel outputs like this means that the ABS sensors will need to be rewired to match this new configuration (Don't want to activate ABS on a wheel that isn't slipping).
DSC_0105.jpg

[AZPete]

When you can road test your set-up please post the results. I've got my ABS plumbed differently but not yet tested. Lots of guys are waiting for results.

[TouchStone]

I'd love to and I will, but I'm many months out from a drive.