[redcat]

We have completely rebuilt the braking system on my 68
cougar. Includes the following:

New brake booster
Rebuilt master cylinder
new front discs
new front calipers
new front pads
new rear cylinders
new rear pads
turned rear drums
new rear brake lines
The brakes worked well until the first hard stop, now the brakes
are poor. The master cylinder is holding pressure, the booster
works, I was stumped. The brake warning light never did work as
the P.O. disconnected the switch on the proprtional valve, problably many years ago.
When I reconnected it of coarse the brake warning light comes on. I resorted talking the cougar to my mechanic who insists that the proportional valve is stuck in one extreme end (off centre)
inside the brake valve and is causing little fluid pressure to the system. He has not been able to move the valve to centre or as it appears at all, and still poor brakes! So........... 2 questions.
First, if the brake proportional valve is seized, can this somehow
block fluid pressure to the brakes, and would a working one fix the problem? Second, what have I overlooked? Sometimes your mind dwells on one thing and overlooks the obvious. :1zhelp:

 

[70XR7ConvertCat]

First thought is bleed the system, you probably didn't get the air out. Second, it seems to me if the proportioning valve is defective or not centered, you'd first notice your brake bias being off (i.e. rear brakes lock first). Possibly the metering valve is defective. This valve delays pressure buildup to the front discs to give the rear brakes time to overcome the return spring force.

1. The way to check the metering valve is to depress the pedal about an inch. At some point you'll feel a change in the pedal effort (a glitch). If you do, the valve is working, move on.

The proportioning valve has a rather involved procedure to center the valve. The brake warning light should come on if the valve is not centered (i.e. a pressure differential exists). For a '67-'69 the procedure is:

2. Make certain brake fluid level is adequate (1/4" from the top).
3. Switch the ignition on. Have someone apply pressure to the brake pedal.
4. Loosen the bleeder screw opposite of the "suspect" end of the brake system.
5. Have your helper depress the brake pedal slowly until the light goes out. Check fluid level, and road test.
6. If problem persists, repeat the procedure on the other end.

If problem persists, re-post, or check for line blockage or contaminants.

Good luck,

Steve C.

 

[redcat]

Thanks 70XR7convertcat!
The system has been bled oh.......... about 7 or eight times,
several times by me and several times in the garage. It can't be air. But you did say the metering valve. Is this the part that is looped into the proportioning valve?? And the cantaminent thing is a great possibility as the car sat in storage for many a year
and the original brake fluid was discolored. Should I remove the
proportional and metering valve and try to clean them? How much
trouble can one get into by taking these things apart? Any
help would be great.
Doug.

 

[70XR7ConvertCat]

If I recall correctly, the metering valve is in the front braking circuit somewhere between the left and right. The line from the master cylinder goes into it, and it splits off from there. I've never taken these valves apart. If they are suspect, I suggest buying a replacement. Brakes aren't where you want to be taking shortcuts.

Steve C.

PS. After bleeding, did clean fluid emerge at each wheel cylinder or caliper? You say they were operating fine until you made your first hard stop. This troubles me somewhat.

 

[redcat]

Thanks Steve

All of the fluid was clean at all four of the bleed screws and
have gone through a litre or two of new brake fluid. I have tried to find a repalcement proportional valve, but have not been able
to find one. I agree with not taking shortcuts with brakes that
is why all of the parts are new and I am troubled and perplexed at this whole thing. I plan on taking off the proportional valve tomorrow to
get a good look at it, it is very hard to see in its location. Also will pull the wheels and inspect the brakes
I will keep you posted.

Thanks
Doug

 

[390XR7]

Hey Doug,if you need a prop. valve I might be able to help you out on that if someone hasn't lifted it already from the car.I'll check on it next time I'm at my buddies yard.then we can hook up and meet one another.

Terry

 

[redcat]

Thanks Terry
You must be online.
I did find one on ebay and at a mom and pops salvage yard
but have not been able to contact them again. How is the 390
running?

 

[redcat]

First the good news. I got the pressure differential valve and brake warning light working like it should. I first remove the
master cylinder, got the headlight door vacuum lines out of the way used line wrenches to disconnect all the brake lines and unbolted the valve from the inner fender apron. Indeed the valve
pin was stuck. I used a tiny punch that would reach down through the end inlet and gently tapped the valve till it moved.
It took more force than you would think! Once the pin was removed it was cleaned and seals inspected. Once reinstalled in the brass casing it moved freely.
Now the bad news. The rebulit master cylinder had been leaking through into the booster. I had not noticed any fluid drop because
I we had been bleeding the brakes about twice a week for the last 2.5. weeks.
I will again replace the master (from a different suppier) and hopefully have enough hydaulic pressure to lock up those brakes.
Will keep you all posted.

Doug

 

[gt390xr7]

Doug, If you have brake fluid in the booster, replace it as well. Unless you like doing the same job twice. just my opinion.

Bruce

 

[redcat]

I value your opinion Bruce. Can the brake fluid go hard on the
booster rubber and shorten its working life? It is so new the
installation stickers are still on it , a few months. I hate to spend that kind of money all over again.

Thanks
Doug

 

[gt390xr7]

If it's brand new, your probably OK. Just try to get it all out and dry before you assemble it. Good luck.

Bruce

 

[Ray]

I have several prop valves F/S. The prop valve does not restrict flow imo. Take yours out and set to center and re-install

 

[gte428cj]

You should check to see if you installed the calipers on the proper sides. Yes the right one will fit on the left and vice versa. If they are on the wrong sides you cannot get the front brakes to work properly and the pedal will be very soft. To determine if they are installed on the correct sides just look at the air bleed screw on the caliper. If it is pointed straight up it is installed wrong. The ait bleed screw should be horizontal and point towards the rear of the car.

All the work you have been doing to get the slider working will not make any difference to your brakes operation. Note the proportioning valve is a cylindrical brass part 2 to 3 inches long. It is attached to the distribution block you have been working on.

The proportioning valve can only effect the rear brakes as it is in the rear brake line. There are three possible malfunctions.

1) No fluid can pass through the valve. In this case your rear brakes wont work.

2) The fliud cannot flow back to the master cylinder. In this case your rear brakes stay on. This will wear the pads down to the metal in no time at all.

3) An incorrect amount of fliud flows. The from or rear will do most of the braking. This will show as faster wear in the front or rear depending on the flow being too little or too much.

You cannot repair the proportioning valve but after market ones are readily available. They are adustable so you have to get it set right for the front and rear brakes to share the braking load.

 

[redcat]

Thanks for all that gte428cj, that does explain very well how the
proprtioning valve and braking system works. The front calipers are on the right sides and after having the distribution block/differential valve apart
and seeing how it is plumbed, it can not affect the brake operation unless there is some massive blockage. But the valve is
now free and the brake waring light stays out. As far as the proportional valve,
it had a crimp on the body by the nut as to prevent tampering so
I did not attempt take it apart and when bleeding the rear brake lines, have all kinds of fluid coming out. As far as the brake performance,
it is hard to get the the front or rear wheels to lock on my gravel
laneway! Don't panic I won't drive it till it is working right.
As I said earlier, the brakes worked well after all the new parts were installed, we drove from Ontario to New Jersey in June and
back, on the way home had to brake hard and went from bad to
worse. Will try another master cyl. as soon as possible. Holiday here on Monday.

Doug

 

[redcat]

Update on bad brakes.
The new M.C. made NO difference in braking. The pedal feels,
just O.K. but not perfect. The front rotors and pads look great, no leaks and the rear drums (still FoMoCo) and pads, spings etc. look great, no leaks. I have new front and rear flex lines ordered.
The only thing I can think of is these rubber lines have gone..........
all funky inside and collapsed. Will keep you all updated. I want to get this thing stopped.

 

[FarmerDave]

Hello Redcat, f your still on the forum please let us know what the problem ended up being.

Merry Christmas