This is very normal for the stock prop valve. The Cobra needs much more rear brakes than the Mustang. The easiest solution is to gut the stock prop valve. To do this you have to pull the nut off the front of the prop valve and pull the spring and check ball that are in it. doing this you will need to replace the nut with one that comes in the FFRP 2300 brake kit. Or you can take the nut to a good tig welder and have the hole in it that has the rubber plug welded up. Then remove the nut on the rear of the prop valve and remove the spring and check ball, then reinstall the not. The turns the prop valve from a prop valve to a distribution block. Your brakes will work much better.

 

Thanks Gordon,

This has been annoying me for about 3 months, And the bodys getting painted monday. Hopefully it will be on the road in a couple of weeks.

Scott

 

there are a couple of possibilities depending on how you are testing the rear brakes. if you jack up the rear, press the pedal and can turn the wheels by hand (in neutral of course), then there is a hydraulic problem i.e. really no rear brakes. this could be because of a blockage in the line, or problems with the calipers, prop valve, or prop block, or maybe even air in the rear line?

if you are saying the fronts lock up before the rears in a street test, then first of all that is correct. you want the FRONTS to lock up first. how far the rears are from locking up you cant tell easily using this test.

if you have performance pads that require a little heat to increase their friction cooefficient, then the front brakes will heat more quickly, in effect changing the bias to the front, but once the rears heat up also it may restore the bias.

mostly what i am saying is that the stock brakes should work quite well if they are working correctly as designed. as i kept telling cobra earl (is that right?), if his brakes sucked that bad then there was a problem with the installation, which turned out to be the case. its worth going through and verifying ehat you have before you start changing parts and engineering.

i still have the stock prop valve and my brake balance is just fine (i do have a faster heating and higher Mu pad in the back than in the front).

YMMV,

james

 

Thankyou James...

One question, do you have drum or disc rear brakes??

IF you can lock up either end, you are alot further along than some people are. problem should be easily solved.

The Mustang manual says the purpose of the Proportioning valve is to keep the rear brakes from locking up on a MUSTANG.

Gordon, what you reccommended does not turn the brake system into a single system does it??

earl

[ April 26, 2003, 08:04 PM: Message edited by: CobraEarl ]

 

Earl,

I have drum brakes . I can jack it up, put it in gear, smash the brake pedal really hard, and it doesnt even slow the tires down a little bit. Funny part is, I can bleed the brakes and I get good fluid flow through to the rear cylinders. The only thing thats left to replace is the prop. valve. Any other suggestions? Scott

 

It does turn it into a single system. In the past I have done this on drum brake cars and found the brakes very balanced. If you go to rear disc, You will need to add an adjustable prop valve to the rear line so you can dial up or down to rear brake pressure.

 

Originally posted by Gordon Levy:
It does turn it into a single system. In the past I have done this on drum brake cars and found the brakes very balanced. If you go to rear disc, You will need to add an adjustable prop valve to the rear line so you can dial up or down to rear brake pressure.

Before id turn my car in to a single brake system, Id remove the proportioning valve entirely. then you will have two separate brake systems.

You have not lived until you are approaching an intersection, you hit your brakes and you have NOTHING. Which is what you can have with a single system. d

Later, if you need a rear proportioning valve, Id add an aftermarket one.

DID you adjust your rear shoes out with the adjuster??? You could be running on just the tips of the shoes... If the car is not on the street, the automatic self adjusters will not work.

earl

 

Scott,
Check this site for info on how to remove the proportioning function of your combination valve without defeating the safety function. Ford makes a kit for this, BTW.:

http://www.svo73mm.cjb.net/

Click on the Fox Body Mustang MC and PV Upgrades and scroll down that page. it has instructions and the Ford part you will need.

Also see this thread:
http://www.ffcars.com/ubb/ultimatebb.php?ubb=get_topic;f=1;t=017894

Forrest

 

Heres what I found:

When I took the valve apart to "gut" it, I couldnt get the rod out on the front brake side. Had to plug off the other ports and use the air compressor to blow it out of there. There was quite a bit of crud in there, so I cleaned it good and put together without the rods. Bled the brakes, and they were a whole lot better. I'm now going to put the valve back together and try that again. Now on my 6th bottle of fluid.....

Scott