North American Turbocoupe Organization



86 Tbird Brake proportiong valve?
RDOG Offline
Posting Freak
#1
Guys, I may not be saying this right, but I think I need one. I replaced everything form the brake booster, MC, brake wheel cylinder pad, and drums. I bled the system 3 times and I still have no peddle! Peddle is nice and hard until I start the car, then the peddle just sinks to the floor. The car will stop, however the peddle is completely against the floor.

The only thing I havent replaced is that thingy between the MC and the barke lines leading to the calipers. I was told its called the brake proportioning valve. Is this the possible problem? Can these be purchased at the local parts store or even a Ford dealership?
1986 Turbo Coupe. Boport StageIII head, Boport 2.1, Performance Techniques 50 trim hybird, StageII.63, stinger 3" exhaust, Phenolic spacer, Boglog header,NPR FMIC intercooler setup, kirban fpr, bigrmotorsports fuel rail, diablo water meth kit, CAI, remote mount TFI, CHE rear adj control arms, MAC girdle, 8.8 rear disc, aluminum drive shaft, H&R lowerings springs Tbird Turbo Specific, y MAS!!
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grey88smokin Offline
Posting Freak
#2
Should be the prop valve on the line to the rears. I can't imagine it is the problem though. Sounds like a leak or bad MC.

Well I am not much help but you can get a willwood prop vavle. Not sure if there is a difference between the Tbird and Mustang on the lines but I do doubt it will cure your problem.

When did this problem appear? Was it just random?
84 SVO 1C
08 MKZ
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Jeff K Offline
Administrator
#3
I am assuming you correctly bench bled the new MC before installing it?

The prop valve isnt the problem. A bad valve would cause problems like long stopping diatances, premature rear lockup, etc, but would not cause the pedal to go to the floor.

I am guessing either you still dont have all the air out, or your new (rebuilt, I assume) MC is bad out of the box and bypassing internally. It happens. Years back I got a bad reman MC that caused similar problems.
Jeff Korn

88 Turbo Coupe: Intake and exhaust mods, T3 turbo at 24 psi, forced air IC, water injection, BPV, Ranger cam, subframes, etc., etc.
86 Tbird 5.0 (original owner): intake, exhaust, valvetrain mods, 100 HP N2O, ignition, gears, suspension, etc., etc.
05 Taurus SEL Duratec daily driver
04 Taurus Duratec (wifes car)
02 Pontiac Grand Prix GT
95 Taurus GL Vulcan winter beater
67 Honda 450 Super Sport - completely customized
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Robert Camp Offline
Posting Freak
#4
Does the pedal go to the floor under steady moderate pressure? Does stomping on the pedal hard and sudden cause it to go to the floor? Try both in the drive way with the engine running.

It could be the master cylinder seals are not sealing properly, allowing fluid to escape around them. It happens on older MC seals as they age and absorb moisture from the fluid, but a new MC could possibly have bad seals from sitting too long on the shelf. Try the above and report back. I too don't think the prop. valve would cause the kind of problem you're seeing. It's a multi-function valve, it also is used to sense a failure in either the front or rear hydraulic circuit and warn you via the idiot light.

Since you changed the rear wheel cylinders, make sure the rears shoes are adjusted out properly also. If the rear shoes are not close to the drum to begin with it takes a lot of fluid to move them out into engagement. I've experienced that a lot. The self adjusting mechanism seems to a bit touchy about assembly. One thing to check there is the shoe adjuster, does the star that turns out have sharp edges or worn and rolled over edges. If the star is worn the self adjuster slips over the star points. I hope that makes sense to you.

Edit: I remember you mentioning, in another post either here or on TF, a whoosing sound when applying the brake with the engine running. That's somewhat normal brake booster operation. Vacuum is applied to both sides of the booster diaphram. When you press the pedal the back volume is sealed off from the front volume and the back volume is opened to atmospheric pressure. The whoosing sound is the air filing the vacuum.
Robert Camp
'86 Medium Regatta Blue TC, 5-speed, original owner.
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Riverratt Offline
Junior Member
#5
Sounds like a bad MC.. Scary thing, many remain MC's are bad out of the box, or go bad shortly after.
Current Turbo Car, 1985 5 speed TC. TC intercooler,87 TC hood, 3 inch down pipe, cat delete with 3 inch tailpipe, K&N cone, T3, Gillis, Dual piston BOV.

Past Turbo Cars

1-1987 Dodge Shelby Z Daytona
1-1986 Dodge Shelby Charger
1-1985 Dodge Shelby Charger/ Intercooled
1-1985 GLH-T Dodge Omni
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Robert Camp Offline
Posting Freak
#6
Here's a nice link for explaining booster operation and simple ways to check it.

http://www.autoshop101.com/forms/brake05.pdf

BTW, the '86 TC uses a dual diaphram booster.
Edit: The Ford shop manual lists it as a dual diaphragm but all the parts houses lists it as single. Oh well, the Ford manuals are not known for their accuracy.
Robert Camp
'86 Medium Regatta Blue TC, 5-speed, original owner.
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RDOG Offline
Posting Freak
#7
Guys, I took it to a shop for the free inspection, they found an issue, but I wont post it until I try the fix first. I hope they are right. I will be kicking myself if they are, and you guys will get a good laughTongue
1986 Turbo Coupe. Boport StageIII head, Boport 2.1, Performance Techniques 50 trim hybird, StageII.63, stinger 3" exhaust, Phenolic spacer, Boglog header,NPR FMIC intercooler setup, kirban fpr, bigrmotorsports fuel rail, diablo water meth kit, CAI, remote mount TFI, CHE rear adj control arms, MAC girdle, 8.8 rear disc, aluminum drive shaft, H&R lowerings springs Tbird Turbo Specific, y MAS!!
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RDOG Offline
Posting Freak
#8
Well, I just found the problem and both you guys and the mechanic were right. Rear drums have two different size shoes. The smaller ones go to the front, and the bigger ones go to the back part of the drum. In my haste to install, I put both the small ones on one side and both big ones on the other. DUH!!! Thats why the brake were uneven as you guys stated, and I didnt have peddle. Live and Learn
1986 Turbo Coupe. Boport StageIII head, Boport 2.1, Performance Techniques 50 trim hybird, StageII.63, stinger 3" exhaust, Phenolic spacer, Boglog header,NPR FMIC intercooler setup, kirban fpr, bigrmotorsports fuel rail, diablo water meth kit, CAI, remote mount TFI, CHE rear adj control arms, MAC girdle, 8.8 rear disc, aluminum drive shaft, H&R lowerings springs Tbird Turbo Specific, y MAS!!
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