Adding Adj Prop Valve

[Schralper]

Guessing someone here has had some experience w/ this one.
So I got me a summit adj prop valve cuz I wanna replace the one that came w/ the CPP front disc kit, manual brakes. I'm getting some shuddering that seems to be rear drums activating a lil early. Figured I'd add while installing lineloc.
The only issue I'm wondering about is the 3/16" (stock front size) rear brake outlet, as stock rear outlet is larger, 1/4"- 5/16"?.
Anyone had any issues adapting up to OE size line?
I'm wondering it there's gonna be enuff fluid moving thru fitting.

[smashingchuck]

The rear should be 1/4". I do not have this prop valve (yet), but from what I've been told by a fellow board member is that the Summit brand adjustable prop valve has two 3/16" ports for the front and one 1/4" one for the rear.

[jlaird]

Maybe i'm reading this wrong, but can't you just get an adapter fitting?

[smashingchuck]

Originally Posted by jlaird

Maybe i'm reading this wrong, but can't you just get an adapter fitting?

He's worried that an adapter fitting would reduce the flow of brake fluid; at least that's the way I interpret it.

[Schralper]

Originally Posted by smashingchuck

He's worried that an adapter fitting would reduce the flow of brake fluid; at least that's the way I interpret it.

yes that is correct, the summit valve has 1 rear outlet. 2 fronts like stock.
Since the rears brakes are drums they need a certain amount of fluid flow to activate them.
Does the 3/16 out, flow enuff w/ manuals?
That being said, yes an adapter in gonna be needed, as well as 3/16 coming in from MC.
I fingered that someone here had installed one and either found it sucked or the 3/16 outlet wasn't a problem.

[smashingchuck]

I'm glad you bring these issues up, as I will be going through the same thing. What is the PN for the prop valve you have? Is it this one?
http://www.summitracing.com/parts/SUM-G3910/

[Schralper]

WHOA how did you know that's the exact one I got, no really the one pictured is what they sent me
yeah it's the 3/16 fittings that I'm not sure about. I don't mind replumbing the brakelines, but not if I don't have to. Been there, done it.
the only other ?issue? is the psi switch on Summit on is bigger than OE single wire one. I plan on using OE switch.

[Shane]

Since the rears brakes are drums they need a certain amount of fluid flow to activate them.

It's not the volume of fluid that activates a braking system ... it's the pressure.

[Schralper]

Originally Posted by Shane

It's not the volume of fluid that activates a braking system ... it's the pressure.

actually I think i'd both. as you generally get one w/ the other.
from HRM
"the brake pedal pushes on a piston in a cylinder, called the master cylinder. The movement of this piston displaces incompressible hydraulic or brake fluid. The fluid flows through hoses to wheel cylinders, which push the brake pads against the drum or disc on the wheel. One advantage of the hydraulic brake system is that when properly combined, the piston size of the master cylinder and the wheel cylinder can multiply the force at the brake pads, so stopping the car is easier."
"If you need to press on the brake pedal with all your might just to slow the car, you probably have a master cylinder with too large of a piston diameter or a pedal ratio that is too low. If you have excess pedal travel, the piston size in the master cylinder is probably too small or the pedal ratio is too high. "
So the way I'm reading this is the MC controls psi AND vol. flow (displaces incompressible hydraulic fluid) to wheel cyl/caliper.
MC piston to big not enuff psi, though vol moved maybe more.
to small, psi but excess travel due to not enuff vol.
Vacuum assist just helps increase psi. which makes it easier to brake.
Or???

[cparman]

Please tell us what the brake setup is on your truck. I assume that it is disc/drum manual brake? As amazing as it might seem in today's world, GM really did have some GREAT people back in the day. Like smashingchuck said the line from the prop valve to the rear brakes really should be 1/4". I have done disc conversions, and gone both ways 3/16 or 1/4. If you are having a problem, I would bet the problem will be still there AFTER you work your fanny off to install a different prop valve. Brake chatter/vibration when brakes are applied usually is a drum or disc that is out of round. If I were you, I would drive my truck on a non busy street, and at about 35-45 apply the emergency brake. NOT THE FOOT BRAKE! Pay close attention, and see if you feel this chatter/vibration. I would recommend not leaving the brake on for long. 10-20 seconds, and then release it. If the vibration is there, have your drums check for minimum thickness, and then have them turned. Tell the shop who turns them what you are up to, and see if they find them out of round. IF there is no vibration found when the E BRAKE is applied, then you have a front drum/rotor that is out of round and do the same thing. The PROP valves on our stuff fail because of a leak, or being tripped, and the owner/shop not knowing how to center them. In respect to ANY prop valve, you can use one 3/16 and T it to both front wheels or use both.
Chip

[Schralper]

hey cpar
manual disc/drum, ebc green front pads, ss line replaced all 3 rubber.
fresh wheel cyl./drums/shoes when discs swapped.
i hear ya, i'll double check drums w/ ebrake
it doesn't appear to be drums outta round, as same issue w/ fresh drums.
It's as if there's a just a bit to much rear being applied vs front especially from 35-15. It doesn't pulse or feel strange thru pedal. Brakes work fine just a lil jerky/shudder, almost like abs when it pulses.
No side to side, seems straight forward pulse.
No my discs aren't on backwards either.
I just didn't know if there was gonna be enough of a restriction on flow w/ 3/16 out vs 1/4 out for rear, as well as the 3/16 inlet vs 1/4 out of MC.
I'm fine w/ the fronts.


btw, from 1wire alt post awhile back, getting truck dialed w/ MAD electric parts.

[XXL]

Originally Posted by cparman

The PROP valves on our stuff fail because of a leak, or being tripped, and the owner/shop not knowing how to center them.

What does this mean?

[cparman]

An over zelous pumper pushing too hard and then you open a rear bleeder screw. Pedal goes to the floor, and get the prop valve out of its normal position ( not centered) then the brakes feel like you have half a brake pedal, and the next time you open a rear bleeder you have no fluid, or little fluid coming out where as before you had good fluid flow.

Originally Posted by XXL

What does this mean?

[DHPmike]

You should be using the one in one out adjustable one. Then yes theres enough fluid and all you do to adjust is do some high speed stops and adjust until the brakes lock up then back them off some.

I have no experience with the two inlet one.

[Shane]

Ok, I'll bite ... how do you "reset" a prop valve.

[joe231]

by equalizing the pressure between the front and rear circuit....

The rear drums do require more volume due to the almost 1:7 hydraulic ratio...if your master cylinder piston is, hypothetically speaking, one inch in diameter and your wheel cylinder is 3/4 of an inch in diameter, the wheel cylinder piston would move a farther distance, and have less psi than the master cylinder piston.....using the same master and a 2 inch diameter caliper piston you would get a 4:1 ratio, so the force at the master would be quadruped at the caliper, and the caliper piston would only move 1/4 the distance of the master piston.....IIRC

[jlaird]

I've got that too. Its from SSBC by the way.