Originally Posted by GalantVR4

OK, I have to pipe in on this. EVERY car with four wheel brakes has a proportioning valve. However, it is usually buried. Older, non-abs cars usually had the P-Valve right under the master cylinder or it was on or near the center of the firewall. Pretty simple deal a brass block with different sized orifices and a "shuttle" valve that also activates that "dual/diagonal" braking system if you blow a brake line. Which is why, when you're bleeding your brakes, you NEVER do a FULL STROKE and bottom out the master cylinder. Then the shuttle valve will go off center and trigger your emergency brake light on the dash. Wilwood makes an adjustable one that sells on ebay for about 50 bucks or so.

Problem is, on OUR cars, and most ABS cars, the P-Valve is built into the ABS motor/control box. (remember where all those brake lines go from the master cylinder?)

Now, on to the idea that you'll wreck the proportioning differences by upgrading calipers. Let's say you throw a set of supra or LS four piston calipers, or even Wilwood or Brembo four piston calipers on. (The Wilwood four piston calipers for sprint cars, brand new from summit, are 129 each and a LOT lighter than the LS calipers) You will, naturally, use a bit more brake fluid per stroke of the brake pedal, simply because the four piston caliper has more internal volume. However, if you kept close to the same PHYSICAL size caliper, it should be close, because the four piston caliper has smaller individual pistons.

HOWEVER, if you get the uber huge piston calipers like the BIG road racing Wilwoods, (as a sample, the TCI big brake kit on my Race Galant VR4 has calipers that are twice the size of the stockers in length as well as thickness, and its pucks are the same size as the stock twin piston) then you run into another, more serious problem -- your master cylinder can't push enough fluid to move the calipers! Which means, you don't STOP.

However, from what I've seen, you'll just get those "Mushy Brakes", no matter how hard you bleed them. This is because you're essentially bottoming out the master cylinder and just missing getting the brakes completely applied. The "MUSH" comes from just trying to stomp that last little bit on the pedal..it is instinctive to do that, but all you're effectively doing is a bit of firewall flexing. Or, you're pushing the plunger down the bore far enough that the bore isn't smooth. The bore has corroded because you weren't using that part of it with the stock brakes and now fluid is bypassing the seals on the plunger internally)

From what I've seen, we don't have a larger BOLT ON master cylinder. One with a longer stroke is not a good idea, because the longer stroke will put your pedal all the way to the floor. The only other way is to find a master cylinder with a significantly larger bore. Problem is, an LS400 and a Supra master cylinder will not bolt on. For some reason, probably a nod at firewall flex, Toyota used a THREE BOLT flange on the SC master cylinder, while using a TWO BOLT flange on every other vehicle they made. So unless you're good at making an adapter flange, nothing else would work. The supra master cylinder would be ideal..even better if there was a TRD m/c, but without the adapter plate, it isn't possible.

Now for the rest of the brake bias story. If you upgrade, normally you will not be using factory brake pads, right? If you do use factory organic or semi-metallic Advance Auto or O'Reilly OEM style pads, you realistically will only increase your clamping force by maybe ten percent.

The advantage to bigger brakes, more caliper pucks, and bigger rotors lies, as was stated above, in the fade resistance given with the increased surface area of the rotor. Plus the extra area and fluid capacity of the caliper also acts as a heatsink. But if you use a performance brake pad for the front, like EBC Greens or reds, or even worse a ROTOR EATING pad that makes the rotor glow cherry red after each stop, you WILL radically alter the brake bias.

Fixing that is fairly easy though, and you do not have to resort to dual piston rears. Just get a more aggressive rear pad. Personally I tune bias BY brake pad material selection so I get exactly the grabbing power and fade resistance I need. On a car that isn't well balanced, like a 67 camaro with a cast iron big block, you'd need that adjustable proportioning valve. However, in our cars, you don't.

So much for brakes 101..
Dave

Originally Posted by Djdot2k

are there any other open nipples on the abs unit?

tried this guy with no luck