Drum Brake Distribution Block

[projectfolly]

I'm sure this topic has been covered, but my search hasnt turned up the definative answer, so here goes.

My '68 Firebird was originally equipped with 4 wheel drum brakes.
I'm in the process of plumbing the car for 4 wheel disc brakes using C5 Corvette calipers/rotors.
The question revolves around the distribution block under the master - is it strictly a distribution block or does it meter brake pressure at all?
I assume it does not affect brake line pressure and I was thinking of using it as is, and installing an adjustible proportioning valve in the rear line downstream.

Thoughts? Opinions?

[rchaskin]

Ditch the factory distribution valve.

Come out of the port for the front and go to a tee and then to each front caliper.

Come out of the port for the rear and go to an adjustable proportioning valve then to the rear tee.

[cdrod]

Ditch the factory distribution valve.

Come out of the port for the front and go to a tee and then to each front caliper.

Come out of the port for the rear and go to an adjustable proportioning valve then to the rear tee.

Randy:
I like the simplicity of your answer, but what if you want to run the factory brake warning light? Is there another way to accomplish this without the factory distribution block?

Rodney

[JustJohn]

Randy:
I like the simplicity of your answer, but what if you want to run the factory brake warning light? Is there another way to accomplish this without the factory distribution block?

Rodney

Yes. http://www.wilwood.com/MasterCylinders/MasterCylinderKits.aspx

[TheJDMan]

My 68 was also born with a 4 wheel drum system and the same distribution block. I replaced the entire brake system including MC and all new lines with C6 Z06 brakes front and rear. The ONLY part that I retained from the original system was the distribution block and I have had no problems at all. This system is not adjustable but it is well balanced and I currently see no need for a proportioning valve. I actually have one of those Willwood proportioning valve kits but just have not felt the need to install it yet. I figure I can always add the proportioning valve at some point in the future should the need arise.

[pist0lpete]

Somebody with more knowledge than I may correct me, but I believe the factory drum/drum distribution blocks shouldn't cause any issues. The ones you need to watch out for are the disc/drum Valves.

[pist0lpete]

Yes. http://www.wilwood.com/MasterCylinders/MasterCylinderKits.aspx
I believe the switch you see there is a brake light switch not a brake warning switch. The warning switch works off a shuttle valve inside the factor distribution block. If for some reason pressure is lost(read a leak) in the front or rear system, the pressure differential moves the shuttle valve over closing off the leaking side of the system. This activates the warning switch.

[JustJohn]

That's what I initially thought as well so I called Wilwood and spoke to a tech. Even after re-reading their instructions I'm confused. Either the install sheet is completely wrong or the tech was, which complicates things as I just finished fabricating/rerouting brake lines.

I'll be checking again now that there's conflicting info from Wilwood.

If I hear differently after a second call, I'll make sure to clarify.

[JustJohn]

That's what I initially thought as well so I called Wilwood and spoke to a tech. Even after re-reading their instructions I'm confused. Either the install sheet is completely wrong or the tech was, which complicates things as I just finished fabricating/rerouting brake lines.

I'll be checking again now that there's conflicting info from Wilwood.

If I hear differently after a second call, I'll make sure to clarify.

I put in my second call to Wilwood and got some explanation which I think helps everyone (disclaimer: I work as an automotive design engineer so I get paid to break things and be wrong 90% of the time. Also I design fuel side components these days.). Here goes:

The GM disc/drum distribution block, which I also had, has a pressure differential switch that gives you a warning when it sees a pressure difference per the GM design pressures. That point is important because when you change the design parameters from what GM intended, the pressure differential switch is no longer applicable to your car. The prop valve feeds into the pressure differential switch, so if you replaced your fixed value prop valve and make an adjustment, you get a warning light because the pressure differential switch sees a pressure difference it was not designed for. I can't think of an easy way to get a pressure differential switch that I could re-calibrate every time I make a change, so I think I have lost my warning light function unless there's one out there that can be plumbed before the prop valve and is looking for equal line pressures.

So after my discussion with the Wilwood tech, the switch that comes with their metering valve is a pressure switch but will not function as a warning light. It's just a pressure activated switch you can use for brake lights if needed.

If someone who is more knowledgeable about brakes sees something wrong here, please correct me on it. I haven't filled my system with fluid yet so it's not messy making changes.

[pist0lpete]

John, appreciate you following up with Wilwood. I agree if you were able to mount the shuttle valve upstream of the proportioning valve it could still function.