FOUR WHEEL DISC PROPORTIONING VALVE

[JETHRO]

did a five lug swap last winter and did four whell disc with cobra brakes. i omitted the stock proportioning valve and replaced it with a wilwood deal for the back. i teed the front and the lines went straight to the wheels from the master cylinder. i used a 95 master cylinder. should i have kept the stock proportioning valve? the brakes dont feel like they should. i had better brakes with the stock master cylinder that pretty much only used the front brakes. im wondering if the 95 master cylinder is bad and im switching to an svo master cylinder.

 

[jrichker]

See http://www.svo73mm.cjb.net/ for all the answers to your brake questions.

 

[Shakerhood]

Yes you should have kept the Original one and gutted the front part and put the FMS Brass Plug in and bought a 3-2 kit from Maximum Motorsports and used it with the adjustable one.

 

[352Ford2]

After I guted my fac porp valve, Insead of buying that 11 doller plug I took the stock one and welded up the hole. Not sure what type of alumium it is but it only really liked the laninated tugnstun elctrode with a fair amout of heat. The pure electrode didn't do so well.

 

[JETHRO]

i dont understand what the diff would be if you just eliminated it. i have both front wheels teed off one port of the master cylinder. does the PV give you better pressure or more pressure? like i said i have the adjustable one for the rear. i figured thats all i would need.

 

[old_blue]

does the PV give you better pressure or more pressure?

it gives the correct pressure to the wheels. You put the adj for the rear b/c you don't want them to lock up before the front.

Since there really is no worry for rear drums locking up before front discs there isn't a need to control the pressure as much in stock form . But since you changed to rear discs you need to be able to control how they work. The stock distribution block (gutted) is still able to balance the pressure to the fronts.

 

[JETHRO]

i believe the pressure is balanced but my problem is it seems like i dont have enough vacuum. i dont have any issues where one front wheel locks up before the other in the rain. the pedal is very firm and hard to push. brand new booster with vacuum.

 

[rowdie- stang]

I did the ford cobra brake upgrade and the only thing that I can see is you should be using a 93 cobra booster. You can still use a stock master cylinder

 

[Mustang5L5]

I am confused on how you have this setup.

You have the front port on the MC T-ed off and running to each of the front brakes and the rear port running to the rear brakes with the prop valve in line with that?

I am not sure that each port sees equal pressure. That could be your problem right there. The way it's usually done is that the two ports from the MC run down to the gutted stock prop valve. SInce it's gutted, any inbalance in pressure is equalized inside the prop valve. From there, you run 3 lines out. 1 to each front brake and 1 to the rear brakes through an aftermarket prop valve.

Now that's how it's usually done, but if each port off the MC displaces equal pressure then they way you have it plumbed should work, althogh i can't confirm. Now if the pressures from each port isn't equal, then you would have a problem

 

[old_blue]

I also think that the distro block compensates for the unequal brake line lengths. But I could be wrong.

 

[JETHRO]

i have the aftermarket PV going to the rear. im getting a cobra MC tomorrow. i mat try to exchange the new booster for a cobra one. if that doesnt work then ill see if i can find the stock PV and gut it.
MUSTANG 5L5- the way i believe it should be is the front port goes to the back and the rear port goes to the front. i sure hope so anyway. thats what the diagram said.

 

[Shakerhood]

I am confused on how you have this setup.

You have the front port on the MC T-ed off and running to each of the front brakes and the rear port running to the rear brakes with the prop valve in line with that?

I am not sure that each port sees equal pressure. That could be your problem right there. The way it's usually done is that the two ports from the MC run down to the gutted stock prop valve. SInce it's gutted, any inbalance in pressure is equalized inside the prop valve. From there, you run 3 lines out. 1 to each front brake and 1 to the rear brakes through an aftermarket prop valve.

Now that's how it's usually done, but if each port off the MC displaces equal pressure then they way you have it plumbed should work, althogh i can't confirm. Now if the pressures from each port isn't equal, then you would have a problem

It is actually a Shuttle Valve and there are guts in the front side and rear side if I remember correct, only the front side gets gutting leaving the rest intact, not a good idea to remove it completely.

 

[JETHRO]

i just tried out the 93 cobra master cylinder and it definitely feels better.

 

[cornholio47]

Ok, i have a question of my own then. The guy that owned my car before me put bigger piston calipers on the car and left the stock master cylinder. to solve this problem I am going to install a SVO master cylinder. Can i still use the stock proportioning valve or will i have to change that. I would think that the bigger bore on the master cyl would not determine the need for a different proportiong valve. the rear brakes are still stock drum brakes by the way.

 

[Mustang5L5]

Yes you still need an adjustable prop valve. Anytime you put different brake setups on a car other than stock, you need different proportioning.

The stock fox brake line setup is terrible anyway. Which calipers do you have up front? Are they the 73mm calipers? If so, the SVO MC is only ideal if you have the SVo rear disk setup as well. With stock drums, it would not be ideal. You actually want a '93 cobra MC.

The stock fox brake setup is plumbed with the front driver's wheel seeing 100% pressure from the MC while the passenger wheel and rear are reduced through the prop valve. That means you have 3 different pressures going to different wheels.

With the Cobra MC and 3-2 conversion, you now send equal pressures to both front wheels and have the ability to dial in your rear pressure depending on factors such as tires and weight. If you have a heavy GT vert or HUGE sticky rear tires, you can dial in more rear bias.

It just makes the braking system "better"