99Hawk120

Some of you may know I've been chasing down a hard pedal and poor braking performance with my current setup:

1LE front brakes
'89-'92 PBR rear brakes
Durastop pads (front and rear)
Stock 92 Master
1990 First Design Proportioning Valve (I think that is right, it's the one that fits the older brake fittings)
ATE Super Blue Fluid

Symptoms:
Pedal is ok but stiff until it reaches a certain point, then it becomes hard as a rock. Car stops ok, not fantastic. Completely unable to lock the brakes even from a 60mph panic stop.

Attempted fixes:
* Stainless steel braided hoses--these made the pedal harder. No improvement in braking noticed yet.
* Brake booster replacement--cured sloppy brake pedal due to worn out booster pushrod. No braking improvement. Pedal is slightly easier to push.
* Soft vacuum line to brake booster replaced with hard line--Jeez, am I pushing on the brake pedal or the firewall? Pedal is easier to depress then before, until it hits the "magic spot", then it is completely immobile. Even with legs of steel you couldn't get it in any farther!

However...

I noticed an interesting thing when bleeding the brakes. The back brakes behave exactly like I think they should. Plenty of pressure when turning the bleeder screw open. Actually, there's more than I expected. But that's not really a problem.

The front brakes, on the other hand... well, the fluid comes out of them at a speed far less than half the rears--I could force fluid through a straw with more pressure! The brake pedal only sinks to the floor VERY slowly when the screw is opened, unlike the rears, where it plunges rapidly to the floor.

Now, all of the hard lines in the car are new. All of the rubber lines were replaced with stainless steel braided a couple months ago. The master cylinder and proportioning valve are new as of when I installed the Ford 9" (less than a year).

So then I asked myself--what the helll is limiting the pressure to the front brakes?

Then it hit me. Someone recently posted here about removing their proportioning valve altogether and the resulting massive improvement in braking power.

It's got to be the proportioning valve. Nothing else makes any sense. The front calipers should be getting way more pressure than the rears. They're not. The car should dive when I stomp the brakes on. It doesn't. Conclusion: The damn proportioning valve is limiting the pressure/fluid flow to the front brakes.

The first question is why. The second question is, what the hell do I do about it? I have an adjustable proportioning valve, but I don't have the tools to install it. But since the proportioning valve is actually a combination valve, what other functionality do I lose if I ditch it completely and use an adjustable one?

ANDYZ28

I installed GM part# 14089496 proportioning valve when I did my 1LE upgrade. It works good for me . The brake function is exactly as it should be.

I hope it helps. ANDYZ28

Jza

Just throwing out a couple ideas:

Accidentally switched the front/rear lines?
Valve and M.S. are used? Could be damaged.
The piston in the M.S. could have popped the seal and the only reason the fronts work at all is the mechanical contact (sort of their backup system). The (!) brake light should come on if that was the case though.

Anyway, just tossing out a couple ideas. Not saying those are it, but that's what I would check if it were me.

99Hawk120

The MC is not the problem. I had to rebleed the master cylinder this time and I noticed nothing strange about the fluid coming from the front OR rear port.

As far as swapping the front and the rear lines, I have no idea how you could do this. The rear line is a different size fitting than the front two (making it impossible to swap the output lines on the proportioning valve). Swapping input lines would be a neat trick, considering the lengths of piping you have to work with; the only way to do THAT would be to install either the MC or PV backwards (not possible in the first case, and the output lines wouldn't line up right in the second case).

I suppose it's possible that I got a defective PV. That would be my luck.

Eightyninef

First I'd try bedding your pads. beat the hell out of them till they smoke. then let them cool and see what happens.

otherwise I'd try another combo-valve.