I have a 1994 mustang that has never had much of any rear brakes. In a vain attempt I had my local shop try to hunt this down (wife's car and all) We ended up replacing
Brake Master, hard lines from the mast to the proportioning valve, proportioning valve, all calipers,all soft lines, Hard lines at the rear axle.
It did not change anything.
This week one of the front hard lines failed and I am i the process of replacing all the hard lines from the proportioning valve back to the rear axle. I have found that getting the lines in to the proportioning valve is a real PITA so I got thinking why not just eliminate it. Pit a t in to the line when it leave the master and run those to the two front calipers and just plumb the line that runs to the rear directly in to the master. I for some reason I need more or less brake I could install a manual proportioning valve in either the front or rear line (what ever one has to much brake gets the restriction) as it exists the master and adjust it as needed. I am thinking that this may actually be better as currently the rears are not really doing anything.
So why should I not do this? Will cats chase dogs will the sky fall. WIll I have no brakes?
Thanks.
A proportioning valve limits maximum braking pressure to the rear wheels - kind of important in heavy braking when all the weight shifts OFF the rear wheels. Rear-lockup + turning = "holy crap."
Just run an adjustable one, so you can decide how much maximum rear braking you can live with. They might be illegal for the street where you are, so locate it wisely.
Don't put it on the front brakes - I can't think of any reason why you would want to limit maximum braking pressure to the front.
You could also look for larger rear brake calipers or wheel cylinders (larger pistons = more braking force).
So after replacing all that other stuff you still didn't replace the proportioning valve? 
For a street car I don't think I'd run an adjustable valve. Too much chance of smacking something while fiddling with it, then billy3esq or his kith and kin will be all over you like white on rice.
The proportioning valve was replaced first in the hunt to get more rear brake. I suspect that the mechanic buggered them while trying to hunt down the no rear brake problem. The problem is that it is a one year only dealer part that is not made by ford anymore. Last time I replaced it it was several hundred dollars. I am a bit POed that the monkey that my local guy used at the time did this. I am going to have to take it up with him but in the mean time I need to get the car running. I guess I have to start searching the local P&P yards.
This is why I want to try to out a manual one in the rears and just T the front brakes off the master. For the $5 in parts it will take I think I am going to do it and see just how bad it is.
Good lord man, don't eliminate the prop valve! You'll end up locking the rears every time you look at the brake pedal.
Ya but I don't have any rear brake now so if I can add some it would be a help. Try driving a car with out any rear brake. Almost as bad as having to much!!!
T front line
adjustable summit prop valve in rear line
win
IIRC, Ford deliberately underbraked the rear to help combat an axle-hop problem.
the only downside to getting rid of the stock prop valve is that the brake light won't light up when you lose pressure in either the front or rear brakes.
another option is to gut the proportioning part of the prop valve so that it functions as a distribution block and run an adjustable valve in the rear line. with a few hard stops you should be able to dial it in.
Knurled wrote:
IIRC, Ford deliberately underbraked the rear to help combat an axle-hop problem.
the oems underbrake the rears to combat the "people that don't know how to apply the brakes and modulate the pressure properly to avoid wheel lockup" problem.
how about softer pads on the rear?
I suggest contacting angrycorvair, he knows more about these brakes than most humans.
novaderrik wrote:
Knurled wrote:
IIRC, Ford deliberately underbraked the rear to help combat an axle-hop problem.
the oems underbrake the rears to combat the "people that don't know how to apply the brakes and modulate the pressure properly to avoid wheel lockup" problem.
On the Mustang specifically, they did it to combat an axle hop problem. It's a linkage issue. The rear anti-dive characteristics do unhappy things.
People found this out in, oh, 1994, when they started tracking the cars and found that the chassis as it is does not like having more rear brake.
The Ford prop valve has two functions. One to control brake line pressure to the rear brakes but the other has nothing to do with this. It is to prevent a total failure of the braking system if you have a failure of a brake line or caliper that results in a loss of pressure in that line. There is a shuttle valve inside the prop vlave that will move in the direction of the line that has had the pressure loss. Shutting off flow to that line and leaving the car with some braking ablity instead of none at all.
Ford sold a special plug that was used to disable the prop valve but retain the shuttle valve function. It came with the Cobra brake kit they sold to retro fit the 13 inch front and 11.65 inch rear brakes on their standard Mustang brakes.
You can get almost any prop valve from any Mustang and use the shuttle valve function with this plug installed and a remote adjustable prop vlave. On most Mustangs, on the fire wall there is a double female brake line connection to the rear where you can install an adjustable prop valve.
For more info I would suggest that you go to a web site called 'Corner Carvers.com" Very knowledgable group with all kinds of cars but heavy on Mustangs!
jimbobski wrote:
The Ford prop valve has two functions. One to control brake line pressure to the rear brakes but the other has nothing to do with this. It is to prevent a total failure of the braking system if you have a failure of a brake line or caliper that results in a loss of pressure in that line. There is a shuttle valve inside the prop valve that will move in the direction of the line that has had the pressure loss. Shutting off flow to that line and leaving the car with some braking ability instead of none at all.
Ford sold a special plug that was used to disable the prop valve but retain the shuttle valve function. It came with the Cobra brake kit they sold to retro fit the 13 inch front and 11.65 inch rear brakes on their standard Mustang brakes.
You can get almost any prop valve from any Mustang and use the shuttle valve function with this plug installed and a remote adjustable prop valve. On most Mustangs, on the fire wall there is a double female brake line connection to the rear where you can install an adjustable prop valve.
For more info I would suggest that you go to a web site called 'Corner Carvers.com" Very knowledgeable group with all kinds of cars but heavy on Mustangs!
Good info. Thanks. I am a member over at CC. I have actually put this brake problem to the people over there a while back and no one could figure it out. I am stumped. The description you gave of how the prop valve should work is exactly what did not happen when my brakes failed this most recent time. Or the time before. The line for the R Front ruptured last week and I had no brakes at all. And this was a new prop valve 3 years back. Previous to this the brakes failed in the rear and the fronts did work.
I am at a loss with this. I am thinking that there may be some sort of obstruction in the lines or a line is pinched in the rear.
In either case the prop valve I have is junk now so I have to do something to get this up and running. About the only "good" thing is that I have made it a point to keep the E-brakes in top shape.
Thanks for the input and I will do more searching over at CC.
Follow up.
I sat and scratch a couple places while I ate a popsicle. Then I remembered a while back I had got a prop valve for a 98 thinking I could use it on my car but when I got it I found that all the fittings were different. They are all the same unlike the one in my 94. AND the mounting bracket was on the opposite side. So the answer was obvious go dig it out. Since I moved recently. .. Well more than a year ago.. . I still have box's of car stuff I have not opened and put away. As luck would have it the first box I opened it was sitting on top!! So all I had to do was go to the lock parts store and get a package of new fittings that I would put on the lines that need to attach to the 98 valve. Now to fix the mounting bracket. This was simple. Cut off the brackett from and weld it back on on the other side. (reason number 1029304820485032 to have a welder) So after gutting the unit to remove all the rubber bits I made the cut V ed the ends and weld it together. I then picked up the proper fittings and started the task of swapping out all the fittings with my double flair kit. BTW pay attention to bubble fittings versus flair. Once I got the prob valve all sorted and plumbed in I got back to the task of replacing all the lines from the prop valve all the way back to the rear axle soft line and to the soft lines at each front corner.
I got all this done and the car back together and decided to call ti a day. I will bleed the system tomorrow.
And just a note autozone sells 3/16 Teflon coated brake line 25 foot rolls for less than $20. Pick up the fittings you need and you can replace all the steel lines the average car for less than $40. Less if you re use fittings from the old lines (I don't do this unless it is a weird fitting that I don't have or the parts store does not stock.
Anyway I went around to all the bleeders several times with penetrating oil. I will hit them again tomorrow morning so hopefully by tomorrow night bleeding should be a sap.
