adjustable proportioning valve questions

Hey guys, been trying to find out some info about adjustable proportioning valves. Have 11.5" disk brakes in the back and would like to get more pressure back there so we can slide the tail around better with the brakes(never sees the road) but had some questions about adjustable prop valves. We have a 2000 booster and m/c and the m/c has two outlets that go into the stock prop valve that then branches to two for the fronts and a single for the rear.

My question is do the front brakes see full m/c pressures and only the rears are metered or does the prop valve meter the front as well? I want to replace the stocker with an adjustable unit but would like to here some opinions on most effective method, and make sure I am not overlooking something, and maybe see some ideas on what would be a good choice as far as the prop valve itself.

What I really want to do is be able to fine tune the front/rear pressures and have them adjustable(possible on the fly?).

Thanks

You might run out of volume for the rear. What size rear calipers? I would definitely run lb residual pressure valve on the rear.

When I built my old Chevelle I ran all new brake lines and a Wilwood adjustable porpotioning valve. I ran full pressure to the front all the time and use the porpotioning valve the reduce the pressure to the rear so they would lock up just after the front tires. With full pressure to the rear I could lock them up very easily.

This is about the only way I could think of you being able to adjust on the fly. You would need to run your rear brake line to this,

http://store.summitracing.com/partdetail.asp?autofilter=1&part=WIL%2D260%2D8420&N=700+4294922533+4294918719+115&autoview=sku

The only other option is a full race pedal assembly with dual master cylinders and a cable bias adjuster like in Nascar or Trophy Trucks. It would be cool.

http://www.kartek.com/Product/Brakes/CNCPedals.html

Thanks guys, actually they are Ford Explorer 11" diskshttp://www.currieenterprises.com/CESTORE/productsRE.aspx?id=1229.

I guess the on the fly thing is not really too important as long as I can adjust them at some point, doesn't have to be while driving.

Hey Ritch, can you add to this: "lb residual pressure valve on the rear"

I am still not quite in the light yet as far as what the prop valve does to compensate for the drums in the rear, are they actuated at the exact same time or is it just bleed off for the rear?

Would love to run those pedal assemblies but unfortunately(or maybe $fortunately$) they are not legal for the class we will be competing in.

I am definitely going to check into some more options as far as the prop valve itself, thanks a bunch guys, much appreciated!
Chris

I've got a Wilwood adjustable prop valve in my 94 (95 booster & M/C, stock 8.25 w/ drums.) Once I got it dialed in, I haven't touched the adjustment.

As far as residual pressure goes, you can get 2 psi check valves to plumb in-line.

A residual pressure valve holds line pressure to the calipers and prevents bleed back requiring less volume when you use the brakes. You install it at the master, they work really good. They are cheap too.

Thanks guys, looking like I have a plan forming.
I'll let you know how it turns out!
Chris

Disc brake systems do not usually have a residual valve in the rear circuit. Disc brake pistons are generally self-adjusting, moving out each time the brakes are applied, and only pulling back a fraction of an inch when the brakes are released. No residual valve is needed. In fact, if you don't remove the residual valve function of the "combination" valve (which includes proportioning), the resulting residual pressure can cause your disc pads to drag, and prematurely wear out.
The residual valve in a drum brake system is to maintain a slight pressure on the wheel cylinder internal cups, to keep them from sucking air back into the system.
Disc brakes generally require more fluid because of the constant auto adjustment of the piston. That's why disc brake MC's normally have near identical reservoirs for the front and rear circuits.
Residual valves are only needed in drum brake systems, and systems where the MC is mounted below the wheel cylinder/calipers.

FordGuy said:

If that were the case, then why do most Race Cars, and High End brake systems install residual pressure valves? because any stock system will bleed back, just from the slight run out alone. When it is in a totally stock system the volume is adequate from the stock master. When you install upgraded brakes that require more volume, it helps to keep the small amount of pressure in the line, requiring less when you hit the pedal. The one thing you always notice in a race car is how high the pedal is. They are also used a lot when you have a low mounted pedal assy. It does cause drag, 2lb max on Disc for the street. I read some where that the fluid by its self causes 1lb just from the reservoir height.

Click to expand...

Keep in mind, it's 2 psi, not 2 pounds. The force the residual pressure exerts on the pad is multiplied by the area of the piston(s). It still won't be a lot, but more than 2 lb (assuming the piston is bigger than 1 in^2).

Also, the residual pressure on the piston resulting from reservoir height is head pressure. It's calculated by multiplying the change in height by the "weight" of the fluid. It will be minimal in this case and may even be negligible.

I meant to say psi not lb, my bad.

I've never seen a technical write-up from a knowledgeable source advocate the use of residual valves in a disc brake system, unless the MC was mounted below the caliper pistons; to the contrary, as the following description points out, there are only two reasons to use a residual pressure check valve:

http://www.streetrodstuff.com/Products/1651/

"----Description:
Ideal for Street Rods, Drag Racing & many off-road applications.

These in-line residual pressure valves from Wilwood retain a minimum brake line pressure to help eliminate excessive pedal travel.

The "Blue" 2lb. valves are used in disc brake applications where the master cylinder is mounted below the horizontal plane of the calipers, and fluid drainback occurs, causing excessive brake drag.

The "Red" 10psi valves work well with drum brakes to compensate for return spring tension in the drums.

They are both made from billet aluminum and are color-coded for easy identification.




P/N Description Price


WIL260-1874 "Blue" Wilwood Residual 2psi Pressure Valve
$17.49


WIL260-1876 "Red" Wilwood Residual 10 psi Pressure Valve
$17.49


= click for more info

Notes:
The lightweight billet aluminum housings have 1/8" -27 threads on inlet & outlet.

Valves prevent fluid drainback in disc and drum systems where master cylinder is located below the floor."

In drum brake trucks, the return spring mounted on the backing plate force the piston to return all fluid back to the reservoir. There will only be head pressure from the fluid contained in the lines, which is inadequate to maintain cup seal in drum brakes. So drum brake systems use residual pressure valves. Disc brakes rely on the piston seal to drag the piston away from the rotor. A residual pressure valve will over come the seal's elasticity and cause the inner pad to drag--not good!
Again, as the above data succinctly points out, residual valves are intended to be used when the calipers are mounted higher than the MC, which would result in the brake fluid draining back, into the MC.

I am not claiming to be a expert on residual pressure valves but can say I see them a lot on offroad race cars, and the masters are mounted very high. I had 2psi on my Pre-runner buggy, and that was suggested by CNC for my pedal bleeding down, install the valves and my pedal was always topped. It did have four piston calipers in the rear, but I doubt that was the reason.