C5/LS1 disc brake proportioning valve question

[BigBlockOlds]

Hello all, been a while since I've posted as I've been trying to finish my '87 pro-touting Cutlass. I'm currently trying to work on the brake lines and brakes some and was curious what type of a proportioning valve should I be running?
I have a C5 hybrid kit up front (C5 calipers with LS1 rotors) along with a stock LS1 rear disc setup. I assume my stock disc/drum proportioning valve won't work properly to maximize everything but is it possible to leave this in place?
I don't want to change the plumbing too much if at all possible. I already need a custom frame line and rear lines.

Thanks,

[Samckitt]

I don't know this to be 100% accurate, but was what I was told to do. Some others will reply I am sure. I have Vette front C5 calipers & rotors with LT1 style rear calipers. I was told to remove the guts from the factory G body proportioning valve & add an adjustable one in the line from it to the rears.

[Apogee]

Just don't run two proportioning valves in one line...if you add an adjustable, remove the OE unit like Samckitt said.

What MC are you running? If you have a residual pressure check valve in the MC port to the rear brakes, like in most GM disc/drum units, remove it so you don't have excessive drag with the rear calipers. If you've got a disc/disc MC this shouldn't be an issue.

Balance-wise, you're a little weaker up front with the C5 calipers (40.5mm pistons) versus the LT1 calipers (43mm pistons) on the smaller diameter LS1 rotors. You can play with friction compounds front to rear though and regain some of your overall brake torque balance without swapping other components.

Tobin

[BigBlockOlds]

Thanks.

As far as a master cylinder, I have a stock MC which I was told would work fine with this setup. I'm using a Hydratech hydroboost setup as well if that makes any difference.

As far as the C5 brakes smaller pistons, will this be noticeable at all? Keep in mind the last time the car was together it had the stock front disc brakes, rear drums and a worn out master cylinder. I would assume, even with the C5 caliper/LS1 rotor that it would still be a fast improvement over the stock stuff.

[Apogee]

Your stock MC should be what is essentially the power brake equipped S10 MC of that era with the stepped bores of 36mm and 24mm respectively. With hydroboost, you should have a very high and firm pedal.

Braking performance should put your old stuff to shame, just be sure to test it out thoroughly and make absolutely certain that the fronts lock before the rears in panic stop situations. You won't really be able to get everything totally dialed in until you've bedded-in the pads and rotors and put a few miles on them...but get it in the ballpark and then go from there.

Tobin

[BigBlockOlds]

Thanks for the help guys.

One last question, when I take the "guts" out of my stock proportioning valve, I assume my brake light switch for the dash will still remain functional?

Thanks,

[Apogee]

Yes, you are correct, so long as you still plumb the rear line through what used to be the port for the prop valve...otherwise you won't have fluid on both sides to balance the switch.

[BigBlockOlds]

Okay guys, finally got around to messing with the proportioning valve and have a question.

What all am I supposed to remove to properly "gut" one? I've removed a couple of plugs along with springs and a plunger but what do I do from there? Do I remove the springs from the plugs and then reinstall?

Thanks,

[86Cutlass383SR]

I'm curious myself what all this entails as I will be doing the same thing.

Doug

[Jameson]

Okay guys, finally got around to messing with the proportioning valve and have a question.

What all am I supposed to remove to properly "gut" one? I've removed a couple of plugs along with springs and a plunger but what do I do from there? Do I remove the springs from the plugs and then reinstall?

Thanks,

I hate bumping old threads especially at 5yrs old, But I am at this exact same point as you... I have C5 fronts and LS1 rears on my car and pulled the combination valve off the frame rail and I don't know what to pull out and what to put back...

Anyone have the response to this?

[ryeguy2006a]

I am curious as well. I am doing the same thing on my car. C5 front, and ls1 rear 1" bore master cylinder and stock proportioning valve.

[Zee]

How about this: http://www.jegs.com/i/Wilwood/950/260-11179/10002/-1