Brake Proportioning Valve

[tonycharger72]

Im just about to finish my brake upgrade and needed some advice about where to plimb in my Adjustable brake proportioning valve,

 

Ive got myself a Wilwood BPV and was wondering where to install it, im using R32 4-spots on 298mm rotors up front and a single piston floater caliper on a 286mm rotor on the rears,

I was going to plumb the adjustable BPV into the rear brake line,

 

But i was wondering what i do about the stock Zed BPV's,

 

I was having a look today and there is two lines that come out of the MS and go into what looks like a BPV, then 3 lines come out of it, one to the driver's side caliper (passenger for the US folk) and the other two go into what looks like another BPV, which then has two lines that come out of it - one to the other front caliper and one to the rear brakes,

 

What i was thinking of doing was re-routing the lines in and from the 2nd BPV that goes to the rear brakes with the Wilwood adjustable BPV - this the best way to go about doing this???

 

Also - what do i do with the stock zed BPV's? i have been reading through old posts and some folks have said to get the best end result you should gut the stock BPV's???

Is this the case?

If it is, how do you gut them???

[Synlubes]

I removed the stock pro valve and mounted my adjustable pro valve inside on the trans tunnel.

You can see the pro valve mounting and brake line mods here

[dr_hunt]

you have to remove the stock BPV or it won't work right.

[Guest zfan]

I own a 1971 240z with an oct. 70 build date. I have heard that there are two on the car one up front and one in the back by the passenger rear wheel under side. Anyone know if there is any truth to this?

 

Only one I could find was under the car by the rear passenger side wheel.

 

Mike

[Phantom]

Mikey - Where's your factory service manual?

 

I don't think the one for my '77 280Z would be the same?

 

dr_hunt - can't you just remove the internals from the stock PV and leave the empty body in place? That would be a lot simpler than a total replumbing.

[JMortensen]

IIRC you can unscrew the guts out of the stock PV and just cut them off. Then put the plug back in. I think that works fine. I removed my stock one and put the adjustable one right in it's place though. Unless you're endurance racing you really don't need to be messing with the PV all the time anyway.

[Phantom]

Jon - that's what I was thinking. My problem now is that the stock PV is right behind hte drivers side head on the LS1 and access is much less than ideal. I may have to opt for an underbody location for the valve that my long arm can reach.

[tonycharger72]

Jmortensen,

 

"IIRC you can unscrew the guts out of the stock PV and just cut them off. Then put the plug back in."

 

So just unscrew the guts and cut them out?

 

I might be wrong about this and it might be something eles, but it looks as if i have stock BPV's, as i described above,

Do i have two? or is one of them something eles???

If they are both BPV's do i give them both the same treatment or do i just remove the guts from the BPV connected to the rear lines???

[JMortensen]

There is only one on a US version 240. There is a plug in the side of it. You unscrew it and you'll see that it has a long needle with a spring on it. Cut that part off, and screw it back in. That's it.

[cygnusx1]

I ran my rear brake line through the firewall and under the center console. I removed the ashtray and put the proportioning valve in the ashtray-well of the trans tunnel. Then I drilled a hole in the ashtray-well and ran the brake line back under the car to the rear splitter.

 

Here it is during the installation:

http://www.280zt.com/extimages/p_P4030096.jpg

 

With the Arizona/Wilwood Big Brake Kit, Dave recommended leaving the stock prop. valve intact in the brake circuit and to just add the adjustable one donwstream in the rear line. It works great this way. The stock prop valve sends too much pressure to the rear brakes when you use discs in the back. The adjustable one allows you cut-back the rear bias.

[JMortensen]

With the Arizona/Wilwood Big Brake Kit, Dave recommended leaving the stock prop. valve intact in the brake circuit and to just add the adjustable one donwstream in the rear line. It works great this way. The stock prop valve sends too much pressure to the rear brakes when you use discs in the back. The adjustable one allows you cut-back the rear bias.

Not so sure I agree with that advice. Any proportioning valve has a tapering off effect. They are not linear in their effect. I don't know what the effect of having two in the system is, but I would think that this would increase the tapering off effect and would lessen the effect of the rear brakes at higher braking pressures. So the brakes might be set up to have the rears lock just after the fronts at lower speeds, but at higher speeds the rears might basically be doing nothing.

 

I haven't tested this so I don't know that what I'm saying is right. But I do know that the guys at Stop Tech don't advise using two valves.

 

http://www.stoptech.com/tech_info/wp_proportioning_valves.shtml

 

Here's what the article says:

1. If you have the deeply-rooted need to install your own adjustable proportioning valve, be advised that they should NEVER be installed if the factory unit is still in place. Proportioning valves in series with one another can do nasty, unpredictable things!

[cygnusx1]

Yes I can totally agree with the unpredictable and nasty things because the pressure can "inchworm" in between the two valves. However, in the case of the AZ kit, and Dave's experience with it, on a 280Z, it seems to work well. I have tracked it and street abused it with no trouble. I get excellent brake control fore and aft with the second valve in the ashtray. I use a ZX master cylinder, 15/16" bore I believe.

[JMortensen]

Still if my theory is right you would have more rear brake available at higher speeds if you removed or gutted the original valve. Not saying what you have now doesn't work, just that if it was done the other way it would probably work better.

[cygnusx1]

I do not totally understand HOW a proportioning valve works. So here is my mental scratch pad.

 

There are only two parameters that can possibly be controlled. 1) Pressure 2) Flow. I don't think that an adjustable proportioning valve controls flow or it would be called a metering valve. Assuming the adjustable proportioning valve can adjust pressure delivered past it, it can only cut back pressure. It can never increase pressure.

 

Pressure Control: It could have a "cracking" pressure at which it would allow NO passage until it's "cracking" pressure was reached or it could simply take one pressure on the high side and deliver a differential pressure to the low side in a linear or curved relationship.

 

Let's say you hit the brake pedal and you go from 0 to 1000psi in the front brake circuit in 1 second. Proportioning valve is set to deliver always 70% of front pressure. Assume the master cylinder creates the same pressure and flow for the rear.

 

Rear circuit possibilities with Prop. valve:

A. The rear circuit goes from 0 to 700psi in 1 second. (pure pressure control)

B. The rear circuit goes from 0 to 700psi in 3 seconds. (pressure and flow ctrl)

C. The rear circuit goes from 0 to 1000psi in 6 seconds. (pure flow ctrl)

 

I don't know which is correct but I think A.

 

IF A is correct, then, two proportioning valves in series would simply step down the pressure through each valve.

 

MASTER-->(1000psi) --> STOCK VALVE-->(900psi)-->ADJ. VALVE-->700psi

 

By removing the STOCK VALVE you are only changing the range of operation of the ADJ. VALVE

 

Also, the speed of the vehicle does not effect the mechanics of the brake system...at least in these cars.

[Phantom]

Every valve, because of its design has a pressure loss across it. An adjustable valve has an adjustable pressure loss. Best comparison would maybe be a globe valve on a water system. There actually is flow in the system that results in the brake pads pressing against the rotor. Like electricity, fluid takes the path of least resistance. If you increase the resistance to flow(pressure drop acoss a valve) then there will be less fluid flow in that direction and more in another. That results in less pad movement on that leg and more on another. In other words, the brakes with the proportioning valve can be made to move less and therefore clamp less tightly on their repsective rotors versus the brakes on the line without the proportioning valve.

[JMortensen]

I do not totally understand HOW a proportioning valve works. So here is my mental scratch pad.

 

There are only two parameters that can possibly be controlled. 1) Pressure 2) Flow. I don't think that an adjustable proportioning valve controls flow or it would be called a metering valve. Assuming the adjustable proportioning valve can adjust pressure delivered past it' date=' it can only cut back pressure. It can never increase pressure.

 

Pressure Control: It could have a "cracking" pressure at which it would allow NO passage until it's "cracking" pressure was reached or it could simply take one pressure on the high side and deliver a differential pressure to the low side in a linear or curved relationship.

 

Let's say you hit the brake pedal and you go from 0 to 1000psi in the front brake circuit in 1 second. Proportioning valve is set to deliver always 70% of front pressure. Assume the master cylinder creates the same pressure and flow for the rear.[/quote']

Read the article. I can't tell you how a prop valve works either. But what I have learned is that "proportioning valve" is a misnomer. It does not reduce the pressure by a factor of 30% across the entire range. There is a "knee" in the pressure drop on the proportioning valves. None of us knows where that knee is until we test a given valve, but basically it will allow a certain amount of pressure up to a given point, then the amount drops off after that point. Dual master cylinders work as you describe, proportioning valves do not.

 

Also, the speed of the vehicle does not effect the mechanics of the brake system...at least in these cars.

True, but you can apply more braking pressure when you're going faster without locking the tires. So the more pressure you apply the more pressure dual proportioning valves would limit, meaning that proportionally you're getting LESS effect on the rear than you would with one proportioning valve. And the reason again is because you SET the proportioning valve at LOW speeds (low braking pressures), but it works to a greater degree at HIGH speeds (high braking pressures). At least that's how I'm reading it.

[cygnusx1]

Globe valve. Yes and no. A globe valve would reduce pressure ONLY if there was flow. Once the flow stops (the pads reach the end of their travel) the globe valve does nothing. This would be more akin to a METERING valve or a restrictor. I think that a brake proportioning valveis more or less like an air pressure regulator on a compressor. Those regulate PRESSURE whether or not there is flow through them unlike a normal flow control valve. I have never had one of those apart to understand how they work nor have I taken apart a proportioning valve so it is difficult to grasp how they work.

[tonycharger72]

"There is only one on a US version 240. There is a plug in the side of it. You unscrew it and you'll see that it has a long needle with a spring on it. Cut that part off, and screw it back in. That's it."

 

Thanks for that mate,

 

I think i figured out what the "other" BPV is...............its got a sensor type looking wire going into it, local 1600 bloke said he was pretty sure it was the "brake pressure switch" or something like that,

 

But either way, i probably should get rid of both of them out of my brake system,

[cygnusx1]

Whatever way you do it, don't test it downhill!

 

Here is a photo showing the location of my Prop. Valve and line-lock (parking brake) in the ashtray.

 

http://album.hybridz.org/data/500/Cygnusx1-interior.jpg

[Dave]

The valve up front on a 240Z with a wire attached to it

is a self centering pressure differential switch that turns

the brake warning light on. The valve in the back is a

residual pressure check valve because of the rear drum

brakes. With drum brakes a ten pound valve is used to

compensate for return spring tension in the drums. With

a rear disk conversion it would have to be removed or

disabled or you will have rear disk brake drag.