Disc Conv. Proportioning Valve

[Burb]

Ok gents... I have just installed rear disc conversion on a 8 lug FF 14bolt on my 1971 C-20 burban from scratch using custom cut brackets, cadillac rear calipers w/e-brakes and front rotors from a 1971 4x4 K-20. My question is ... do I run my newly added rear adjustable proportioning valve before or after the stock disc/drum valve unit and if I run it before, do I have to block off the input and output of the old valve?

Any thoughts would be great.

[N2TRUX]

Anyone?

[55belairtim]

Hi
you dont need a proprtioning valve if you have 4 wheel disc.

[55belairtim]

Matter of fact remove the factory disc drom valve go strait from the master to the barakes, the proporioning valve is to keep your rear drums from locking up befor your front disc's

[Shane]

Originally Posted by 55belairtim

Hi
you dont need a proprtioning valve if you have 4 wheel disc.

And where exactly did you come up with that bit of information?

[cparman]

I tend to agree with 55belair. The reason you have a PROP valve is to compensate for the difference in disc brakes/ drum brakes. I need help here /// drum brakes need a bit of residual pressure ( 2-3 lbs ) so they respond to brake pedal application. Disc brakes are ready right now. and do not need residual pressure. I do know that there are two different PROP valves for disc drum/ disc disc applications.

Some of the mid year Corvettes ( 65-67 ) with 4 wheel disc do not have a prop valve

[Shane]

You can agree with 55belair if ya want, but believe me you will definitely WANT a disc/disc prop valve on your system the first time you hit the brakes in the wet. Just because it has discs both front and rear does not mean it requires equal pressure front and rear.

To compare our trucks to a Corvette is not a reasonable comparison. 65-66 Corvettes also have a LOT different front-to rear weight bias as well as a total weight difference compared to our 1/2 ton trucks. They starting putting prop valves on the 'Vette in '67, so that argument is moot.

Not trying to sound like a know it all, but I have already been down this slippery road. I added the prop valve.

[55belairtim]

I have been selling and building car/trucks since i was 14 yrs old. Yrs of experience dealing with companies like mcgaughys, ssbc, bear,mp, they have all told me in the past you dont need them. Lots of times those blocks arnt proprtioning valves they are just dirtrabution blocks. At least thats what a guy at gm told me.

[Shane]

What the heck does your age have to do with anything?

Funny, SSBC is the company that sold me my prop valve.

[fixit-p]

I would say your adjustable prop valve replaces the stock disc/drum a typical disc/drum prop valve distributes the brake fluid 70/30. 30% of the fluid to the rear disc's would not give you much braking for the simple fact that the calipers volume is greater than the original wheel cylinders they need more oil but 50/50 would cause the rear wheels to lock up due to front to back weight bias. Ditch the original prop install the adjustable and fine tune it.

[XXL]

Originally Posted by 55belairtim

I have been selling and building car/trucks since i was 14 yrs old. Yrs of experience dealing with companies like mcgaughys, ssbc, bear,mp, they have all told me in the past you dont need them. Lots of times those blocks arnt proprtioning valves they are just dirtrabution blocks. At least thats what a guy at gm told me.

My uncle used to be an Amway distributor and I have a scar on my right hand.

[55belairtim]

Originally Posted by shane

what the heck does your age have to do with anything?

Funny, ssbc is the company that sold me my prop valve.

that may be but when i bought my complete kit for my mustang disc brake front rear, booster master, there was no proprotioning valve, i called and asked them about it and they told me that i didnt need one since i have 4 wheel disc. That was about 12 yrs ago. Maybe they changed there mind but i know for 12 yrs now ive been selling and installing these kits i have never used a proportioning valve on 4 wheel discs, never had one car or truck have the rears lock up before the fronts did.

[Shane]

So now we are talking about Mustangs? <double-checks original post>

Another case of a very large difference in the front to rear weight bias of a light & fairly neutral balanced car versus a very disproportionately nose-heavy 1/2 ton truck.

Apples to oranges.

[bw4sale]

I'm no expert, but I have to agree with Shane on this one. It's not just a drum/disc issue. You want your fronts doing most of the work. My brother also had an unfortunate experience when his rears grabbed to much. He ended up sideways in an interesection.

[55belairtim]

did your brother have 4 wheel disc.
shane i was useing the mustang as an example. i know there different, that was just my first experience dealing with ssbc and what they had told me. also my buddy has a 73 chevy truck with 13" big brakes front and rear that i installed, no proportioning valve anywhere and the fronts still lock up before the rears. even if the ground is wet.

[LONGHAIR]

Originally Posted by 55belairtim

my buddy has a 73 chevy truck with 13" big brakes front and rear that i installed, no proportioning valve anywhere and the fronts still lock up before the rears. even if the ground is wet.

You are aware that "lock-up" is not the goal here right? If your buddie's truck had more brake bias to the rear, it might stop better, and have steering control at the same time.

[fixit-p]

Originally Posted by Burb

Ok gents... I have just installed rear disc conversion on a 8 lug FF 14bolt on my 1971 C-20 burban from scratch using custom cut brackets, cadillac rear calipers w/e-brakes and front rotors from a 1971 4x4 K-20. My question is ... do I run my newly added rear adjustable proportioning valve before or after the stock disc/drum valve unit and if I run it before, do I have to block off the input and output of the old valve?

Any thoughts would be great.

Found this on the web, hope it helps...

The SSBC kit is designed to work with the vehicle's stock proportioning valve arrangement, but you may want to fine tune your front-to-rear brake bias by adding an aftermarket adjustable proportioning valve. Brakes stop best when adjusted so the front wheels lock up a fraction of a second before the rears. There are many brands and styles of adjustable valves to choose from, but all are installed in the rear brake line and reduce the amount of fluid pressure going to the rear brakes. Many late-model vehicles have a combination valve that handles rear brake proportioning along with several other brake functions such as serving as a mounting point for warning light switches, bleeder valves, and metering valves and serving as junction blocks. Combination valves must be modified before using an aftermarket adjustable valve. We modified a late '70s Ford combination valve for this story. Other makes may look the same, but function differently, so get a repair or service manual to figure out how yours operates and what needs to be changed.

[XXL]

Originally Posted by fixit-p

Brakes stop best when adjusted so the front wheels lock up a fraction of a second before the rears.

That's just a top brake vendor. What do they know?

[Burb]

Ok...with your input and more research I have ordered a Disc/Disc Proportioning valve from CPP and have installed a single line adjustable proportioning valve on the the rear out line hopefully allowing a bit more fine tuning ... in going without any I feel I would loose that choice, and when I have 3/16" front hard brake line and 1/4" rear hard brake line I think I might need to adjust it a bit to prevent unexpected lock-ups.
I'll let you know how it grabs.

Thanks guys



a mustang ??????

[Shane]

Good luck and be sure to keep us up to date on how it turns out.

[Sinisterspeed]

One more thing. Drum brakes require 10lbs residual pressure where disk only require 2lbs. When you order them ( I got mine from SSBC the Drum ones are anodized red and the disk ones are anodized blue. The residual valves goes in after the prop valve.

[Burb]

So Sinister, you are suggesting I add an additional 2lbs residual pressure valve as well?

I would have thought the new propotioning valve set for disc would already do this?

Never too old to seek knowledge ...

[55belairtim]

hi
sorry for the bad advice, i gave you i was corrected this afternoon about it, if you have adisc/disc combo brake system that has two different size calipers then you do need a proportioning valve, if you run the same size calipers front and rear you dont nessesarily need them. sorry guys for giving bad information, but you learn something new everyday, the reason i never had a problem is i always run the same size caliper front and rear with a disc disc mastercylinder.

[55belairtim]

hope you guys can forgive me.

[Shane]

Originally Posted by Burb

So Sinister, you are suggesting I add an additional 2lbs residual pressure valve as well?

I would have thought the new propotioning valve set for disc would already do this?

Never too old to seek knowledge ...

If you bought a proportioning valve specifically designed for disc-disc application then it should have the metering built in for the residual pressure. An adjustable-type prop valve is more of a "regulator" type valve (controls pressure only) and does nothing in the way of metering residual pressures.