proportioning valve help ???? emergency braking

[jaywish]

Hi Folks,

I did the swap to the later model model front brakes in my 89 wagon and it works fine except the front brakes lock up in an emergency stop. I know many others have said that they had no problems after the swap but I most certainly do. I do not even want to drive it in the rain.

I went to look at the proportioning valve and find there is none, at least not exactly.

There is a "Pressure Control Valve". From the service manual.. "The valve is screwed into the master cylinder. It limits the pressure level at the rear brakes to minimize rear wheel skidding during hard braking. The sedan and station wagon use the same valve."

There is also a "Metering Valve". ... The metering valve limits the hydraulic pressure to the front disc brakes untill a predetermined front hydraulic pressure has been reached. The valve has a bleeder rod for purging the front brake system after performing brake service. Refer to Hydraulic System Bleeding."

So it seems to me that there is really only a limiter for the rear brake pressure which screws into the master and then there is a valve for the front that keeps the pads from rideing the rotors untill a certain amount of pressure is applied.

So what to do?

I could try to add an adjustable valve between the master and the metering valve. That would allow me to reduce the pressure to the front brakes.

I could try to disable the pressure control valve and add an adjustable valve between the mc and the splitter for the rear brake line at the differential thus increasing the pressure to the rear brakes.

I could rip out the front upgrade and go back to pre 98 brakes.

At first blush increasing the pressure to the rear sounds good except that I wonder if that will just achieve easier lock up of all four wheels.

This is something I really need to take care of quickly though my plate is full and can not afford the extra time working on the wagon right now.

[Brown_Muscle]

Just a thought...you have massive "high performance" brakes now...lockup of the front should be very easy...you may just have to relearn the pressure of the pedal to achieve optimal braking performance without locking the fronts up..since you don't have ABS....

[jaywish]

Well I had been thinking about that except that now the fronts lock but the rears do not so the car slides.

I have slid into severeral intersections in the rain. I have been driveing this car for about ten years and my stopping distance is now much worse then before.

So I do not think that is is the answer but I thought about it quite a bit myself.

Though you are right of course. The front brakeing performance is very likely improved. The problem is that I have unbalanced brakeing now so in the end things are worse than they were with the stock setup.

I do need a new rear and likely rear disks but am out of time to work on this car. I can not do another project on it now unless I want a divorce. Even then I would have even less time to devote as the process of divorce would be all consuming. It has to work and it must be accomplished in a short amount of time.

[gadget73]

are your rear brakes working properly / at all? I have a very hard time locking my fronts up. When I had the late front brakes and my stock rear drums, the back brakes would lock up chronically, but never the fronts.

All valving is on the rear brakes. The fronts go straight from the MC to the calipers. The valving only really needs tweaking if you fit rear discs to the car in order to make better use of them. They work with stock valving, but its not optimal. No change to the fronts though.

What pads are you using? Are your front caliper slides free?

[jaywish]

All good questions, the fronts seem aok, in that they are not dragging. the pads are centric semi metallics all new rabestos semi loaded calipers and centric premium rotors.
The rears work though I occasionaly get a small rear oil leak on one side. I do not believe that is the problem as the side that is always dry does not lock in conjunction with the fronts. When I say they work, they stop when the rear is in the air and you hit the brakes. All new wheel cylinders, shoes hardware and springs about 6k ago.

I used to have a hard time locking up the brakes, before I did the swap.

You are correct the only real existing valving is to restrict the rears.

[rellik god]

hey jay is your mc for a abs car or is it for non abs.thoese screw prop valves are differnet they are different valving i believe.also when i did my brakes i got ride of the frame prop valve

[jaywish]

hi,

The 89 has the standard original non abs type mc. The car does not have a frame type proportional valve. It has the mc screw in restrictor for the rear and the minimum pressure switch for the fronts.

If the abs rear screw in restrictor has different valving I wonder if it would be a better match for the newer brakes? Then even if that is true, then maybe replaceing the rear splitter with an adjustable valve would do the trick.

Has anyone defeated the rear screw in restrictor or at least examined it?

[gadget73]

I think the ABS master cylinders are actually different. I don't know how or what, but they aren't the same. Also not sure about the valving either. I don't think I'd try running ABS valving without ABS though. I also would not recommend using disc brake valving with drums. They aren't entirely compatible.

[jaywish]

I am leaning to trying to defeat the rear restrictor and adding an adjustable valve for the drums. I am not sure if it will rectify my problems but if it does then I would be one step closer to rear disks.

Has anybody defeated the rear restrictor? If so how?

Does anyone have an old one around? I coluld prepare it and just swap when I do the job.

Jay

[gadget73]

I changed the whole booster, master cylinder, and valving over to late model stuff when I did that. No adjustment, just stock Ford parts off an 02 model.

[jaywish]

Well I ordered a wilwood adjustable valve and a wilwood 10lb. residual pressure valve to keep a little pressure on the shoes. I need to turn up a stock rear restrictor to defeat. Assuming I can defeat the restrictor, it should be a fairly simple job and I believe it has good potential for sucess. (fingers crossed)

A newer style mc setup would probably work. I think it would have had the later model rear restricter which may have done the trick on it's own.

I can take out the residual valve when and if I get to upgrade the rear brakes and still retain the adjustable valve.

[sly]

IIRC from the master cyl change on my truck... that rear line restrictor is just a plastic bits in the hole in the MC. take it out and you'll need to drill out the thing (it has a tiny ass off-set hole). You'll need a vice on a drill press to keep the thing centered. Once that is reamed out, it's well and truly defeated.

[sick88tbird]

IIRC from the master cyl change on my truck... that rear line restrictor is just a plastic bits in the hole in the MC. take it out and you'll need to drill out the thing (it has a tiny ass off-set hole). You'll need a vice on a drill press to keep the thing centered. Once that is reamed out, it's well and truly defeated.

Been there, done that! We brought a Villager back to life to donate to a "half-way" house for battered women and on the final test drive before handing it over, we noticed the brakes dragging...left front and right rear(diagonally split system), and it had one of the line restrictors on the master cyl for that fluid circuit but not the other....after plenty of searching, turns out new replacements are not available....put it in a vice and proceeded drilling it out...what a PITA that was! Get so far along and then all the little plates and pieces want to just turn inside...we ended up getting it though and the van stopped fine afterwards...

Those things can do goofy things when they fail.

FYI, converting to rear discs, then using a factory type disc/drum prop valve(with the secondary side gutted and rubber plug blocked off) with a cheapo summit or wilwood adj. prop valve downstream in the rear fluid circuit works perfectly and allows you to tune in the front/rear bias beautifully. A factory type prop valve does a lot more than just direct fluid around...they have what's called a "slew" valve inside them that allows more pressure to the front brakes as you get harder on the brakes(as the nose dives and weight is transferred to the front). With the adjustable valve downstream, you're not just adjusting the rear brake pressure, you're also changing how the fluid pressure is affecting the slew valve in the factory type prop valve. That allows you to truly dial it in for a nice feel...it is easier to use a later model disc/disc type prop valve if converting to rear discs, however I'd still recommend an adjustable prop valve downstream and the slew rate in that prop valve is most likely different than the earlier disc/drum set-ups and you'll need more rear pressure than what that disc/disc prop valve will give you considering the fact you have more rear axle weight than any sedan ever did.

Good luck!
-Don

[jaywish]

I am linking this thread back to my original thread on the big brake upgrade. I will post pics and results there when it is done.

http://www.grandmarq.net/vb/showthre...-with-glitches