Saved from the Demo Derby: 1990 Country Squire

[gadget73]

prop valve should be screwed into the side of the master cylinder where the rear brake line attaches.

[Tiggie]

prop valve should be screwed into the side of the master cylinder where the rear brake line attaches.

That thing is there... didn’t realize it was a proportioning valve. Now I question if it’s working...

[Tiggie]

New master cylinder installed. Brakes feel much different and seem to do equal work. That said, the new feel is much more like my 88 - not inspiring. The old reservoir has a lot of sludge in the bottom which may have contributed to the initial problem of mostly rear brakes only. I cleaned it out but I used a new reservoir because I had one.

Chased the code 33 KOEO. Found the EVR vacuum line unplugged. Oops. Fixed that and got a happy code 11. Runs better again without the vacuum leak.

It’s a dream to drive. It’s like Dr. Jekell and the 88 is Mr. Hyde has far as road manners. So glad this one didn’t get smashed and crashed.

[Tiggie]

Drove this today for the first time since July-ish. Started and drive fine. BUT...

The rear brakes are still screwed up. They are dragging and getting very hot, both sides. Panic braking results in rear lock up. The front brakes are doing very little. The brake pedal has very limited travel before the rear gets locked up.

Here’s a list of things that have been done:
The adjusters are 95% screwed in. Temporary relief of symptoms until driven.
New wheel cylinders
New master cylinder. Temporary relief of symptoms until driven.
Cleaned the funky valve thing that screws into the master cylinder for the rear brakes.

I checked yesterday to see if there was any residual hydraulic pressure at both the master cylinder and the wheel cylinder. I don’t have a gauge but simply opened the fitting at the master cylinder and at a separate time, the wheel cylinder bleeder. Neither seemed to be holding pressure.

My next check is the parking brake adjustment. Any other ideas?

[gadget73]

the rear brake shoes aren't on backwards are they? There is a front and a back shoe, and if you reverse them the brakes are prone to lockup. The front shoe has a shorter strip of friction material.


If its mechanically right, only other thought is the prop valve is bad. I think 90 has the one screwed into the side of the MC instead of the block on the frame, but if it were not reducing pressure to the back you'd get these problems.

[Tiggie]

I will pull the wheels to check the the shoes. I put them back as I found them but someone had did the brakes before the car entered its stationary slumber in 2008, and could have put them back wrong.

It does have the valve in the master cylinder with no other proportioning valve. When I cleaned the valve, there was a small plastic restrictor in there that moved around loosely. Not spring loaded or anything. Been meaning to pull one from a junkyard car to compare. And swap into this car to see if it made a a difference.

The parking brake cable was plenty loose. The parking brake does work normally and requires quite a bit of parking brake pedal travel.

[gadget73]

lots of pedal travel would go with the adjusters backed out. The parking brake actuates from the bottom too, so the shoes being backwards wouldn't bother it.

curiosity test, does it act the same in reverse? If its a shoe issue I'd expect different behavior that way.

[Tiggie]

Haven’t done anything else to the car since that requires time and a yard that isn’t a swamp (currently artic swamp with a foot of snow).
Been researching though.
No boxes at the local junkyard. Was looking for one of those valve things to screw into the master cylinder. Found one on a 1994ish F150. Decided to try to find some interchange information.
1988-91 boxes uses E8AZ-2B257-A. It is called a “brake pressure differential valve assembly”. Not available new from anywhere so it seems.
The 1989-97 F-Series uses a F8UZ-2C161-AA. It is called “brake master cylinder fluid control valve”. Available new most anywhere (Amazon, eBay, Ford, etc).
I’m hoping they have the same function.

Stolen from http://www.diesel-dave.com/vehic/man...j/stj69b03.htm
The brake pressure control valve regulates the hydraulic pressure in the rear brake system. It is located between the rear brake system's inlet and outlet ports in the main valve. When the brake pedal (2455) is applied, the full brake fluid pressure passes through the brake pressure control valve to the rear brake system until the valve's split point is reached. Above its split point, the brake pressure control valve begins to reduce the hydraulic pressure to the rear brakes, creating a balanced braking condition between the front and rear wheels to minimize rear wheel lock-up during hard braking.In case of the front brake system malfunction, the brake master cylinder fluid control valve has a bypass feature, which allows full hydraulic pressure to the rear brake system.

I will likely swap the used F150 valve on in the next couple days but won’t be able to test results for several weeks while, if, the swamp dries out a bit.

[jaywish]

They also provided a residual pressure function. Calipers actuate faster than drums so the drum half of the system is kept under pressure so it actuates faster.

[sxcpotatoes]

They also provided a residual pressure function. Calipers actuate faster than drums so the drum half of the system is kept under pressure so it actuates faster.

Yep, when I was gathering parts for my stalled '62 Willys Jeep project, I ended up getting some one-way in-line valves which retain 5 or 10 or 15 psi (I forget the precise number) in the brake hoses up by the drums or whatever to keep the 4 drum brakes closer to engagement. I learned to drive stick on my brother's '79 F-250 w/300-six. Stopping that beast with 4 drums when driving in today's traffic required a lot of advanced planning and filling out a request in triplicate. Especially when my car went down and I had to borrow it for a month, in the snow.

[Tiggie]

I am concerned it’s holding too much residual pressure.

Truck parts don’t fit. The part that screws into the master cylinder is a much larger size on the truck. Possible I could do a truck master cylinder conversion...

The original valve seemed fine when I had it out. Moves in and out freely. The truck version seems to function the same.

Still need to check to see if the shoes are backwards.

[Tiggie]

Finally a break though on the brakes lol.

Drove it this afternoon. Flawless brakes. Set the parking brake and let it off, and the problem was back!

It has to do with the parking brake mechanism, which apparently has a self adjustment in the 90+ design from what I can tell. I can tug on the parking brake cable under the car and loosen the brakes up. They are fine until you use the parking brake. Each click of the parking brake mechanism results in tightening the cable. Letting it up, either manually or with the vacuum auto release, does not allow the cable to loosen. You can push the parking brake again, upon which it continues to tighten the cable. Release - and again no loosening of the cable. The rear brakes are very tight at this point with the brake released. On the third parking brake use, the cable is already tight, tightens slightly, and upon release, releases back to just being tight. The cable seems to move freely manually and isn’t rusty.

I’m going to attempt to pull the mechanism out tomorrow and take a look at what’s up with it. If there is something that engages/disengages the self adjustment, it is not working...

Anyone play with one of these 90+ mechanisms before. Looks quite different from the one in my 88.

[Tiggie]

Got my Chilton manual out since I don’t have a Ford manual for the 90.

To get the parking brake mechanism out on an 89-, it’s five easy steps. On the 90+, it’s 13 steps, including loosening the dash and pulling it back. F-word that.

The 90+ is adjusting in the mechanism. There is an adjustment procedure to follow for a new mechanism. I will try that first.



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[slack]

I had a similar issue with my '91 GMQ. The parking brake would tighten up when you pressed the pedal in but wouldn't slack all the way back out. One time it got completely jammed up when I was parked on a hill and ended up just having to cut the parking brake cable under the car to get it to let go. Even after doing that, my pedal portion was still jammed up so something must have been stuck on that side? Unfortunately I never really dug into what was broken about it. I drove the car with the sheared e-brake until the end.

[gadget73]

If you do end up pulling that pedal assembly out, would you mind letting me know how different it is to standard box e-brake pedals? I've halfass thought of converting mine to a newer style so I could use common off the shelf parking brake cables with the rear disc swap. Not like I actually use the parking brake ever.