Thread: Proportioning Valve? Dual inlet/outlet vs Single inlet/outlet

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I am collecting parts for a master cylinder upgrade in my heavy Chevy and I see the need to install a proportioning valve, but am confused as to whether run the type that have a dual inlet/outlet to manage both front and rear brakes. or just use a single inlet/outlet valve on the rear brakes...

Which do you guys prefer? Any advice?

I usually just run the single on the rear line, works good for me... The entire system works best with residual valves used in conjunction with the proportioning valve....

I think it depends on your setup. I have all disks so I used a gm factory m/c and prop valve, rod and pedal assembly. which has a 2 in/out set up. But I have a buddy that just has a wilwood prop valve in the rear line with no problems.

on the Nova it looks like we have a factory MC, manual, but we have 4 wheel discs. I'm guessing I need 2 residual valves and a proportioning? any input appreciated, I like going fast but love being able to stop.

Red

I believe a residual valve is only needed if the MC is mounted below the slave cylinders (like under the floorboard). They prevent the fluid from draining out of the slaves into the MC due to the effects of gravity...

Mine is up on the firewall still, and not power either, if that matters.

Dago, if I were you...Id go with one p-valve on the rears with no residuals. That's the route I am going to do on my car. Maybe someone else will chime in and tell us we are on track or clueless...

I've got 3 set this way, Master on the firewall,Single p-valve on the rear line , no residual valves --not a problem.

Do you mean to run a 4 line or a 5 line combination valve?

A combination valve is both a proportioning valve and a metering valve or "hold off valve" together.

The proportioning valve is used in the rear to decrease the rate of pressure rise to the drums relative to the pedal force as weight is shifted to the front during braking. This prevents the rear from locking up under hard braking conditions.

The metering or hold off valve is used in the brake system to better balance the front to rear brakes. The valve does not allow the pressure to rise at the front disc brakes until the pressure at the rear drums has risen sufficiently to overcome the brake shoe springs. At this point the valve opens to allow full pressure to build at the front brakes.

A 4 line has a front line in, and a line out to a "T" to both front brakes & a line in for the rear and a line out to a "T" for both rear brakes.

A 5 line has a line in for the front and two lines out for the front brakes, one to each brake to balance them out side to side better, a line in for the rear and a line out to a "T" for the rear brakes.

When ever possible never run a Residual valve, unless your MC is lower than any wheel cyl or caliper. It will hold unwanted pressure against your brakes and cause extra brake wear.

Pat

Pat for 4 wheel disc, non power, is it just a standard one in one out proportioning valve that I need?

I know the factory setup on the disk/disk configuration is the 5 line valve. by running this, I've had no bias problems when braking. for my degree of knowledge and my individual needs, the factory engineering was just the ticket.

Dago Red,

The proportioning valve was necessary in the disc/drum set up to compensate for the delay of the rear drum brakes. Since there is no delay in the rear disc set up only a block is needed to separate the front and rear systems (with a dual line MC) and activate a warning light in the event of failure, if you want a warning light. Which is simple to wire.

An adjustable proportioning valve in the rear line can be used to set front to rear reaction time if you find it necessary to tweak the braking of the car. Under braking, most vehicles transfer more weight to the front wheels. When this happens, the rear wheels lose some weight and can lock up if the pressure is too great too quickly in the braking.
Eventually full pressure is applied to the rear brakes through the proportioning valve, if it's a factory or a aftermarket or a adjustable.

Are you using a dual line master cylinder? You should, in case one end brakes a line, or pops a wheel cylinder, or any leak, you'll still have brakes at the other end, hopefully the front!

If you want to stop better/quicker, add power asst, or larger front disc setup.

Pat

Pat, Thx for the info. I am not sure what I was actually looking at. The item I initially saw was a GM proportioning valve that had 2 ins and 2 outs with a safety light switch. Now that I know more about what these things are, Ill go back and do some more snooping.
Thx again -Joe

My 68 suburban has a block with one-in and one-out on each end (total four fittings) appears to be blocked in the middle where an electrical sender is. There doesn't seem to be anything else inside. Is this the right piece for front disc?

AzDon,
Is it a stock setup, or did you switch it to front disc's?

The factory 1968 drum/drum master will have the residual check valves built into the master, and have a failure block (sounds like what you see) When you get a leak it will move to the low pressure side trip a switch which will turn on the light on the dash.
You should add a porportioning valve to the rear brakes, if this is a none factory setup, because a drum/drum setup did not come with one!

A combination valve is both in one, plus has metering valve to the front wheels.

Picture is of what you have now, and if it is a factory disc setup, there should be another block in the rear line after this block, to the rear brakes which would be the proportioning valve.

The other picture is of a combination valve with 5 lines.

Pat