Proportional Valve and MC leaking Brake Fluid

Old Goat

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Jan 14, 2021
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Northern Nevada
I started another Thread of a soft peddle and leaky Brake Line. Was never a big leak, just some slow drips. MC never ran dry, but low peddle etc...
thread went to 4 pages, and sort of drifted off...

Then the MC started to leak, had a drip in another area, saw it running down the edge of the inner plastic fender, and also running down under MC on the Booster. OH Great.
Here is that thread where I up graded from the older MC to the later Aluminum with clear Reservoir.

I feel the 2 above threads tie in with replacing the P-Valve that is leaking.

Last week I dropped the T-19, to do a Clutch replacement and rear Main Seal. Now with that out I could see up under the P-Valve area where it is wet with Fluid.
blew it off with carb Cleaner and wiped it with a rag. Checked it later, and on the rear of the Valve is a hex shaped piece where the rear brake line connects. On the bottom of the hex looks like a small rubber plug, and that is were the leak is, not the Brake Line like I thought in my above thread.

Having the truck jack up for the Clutch job makes it easer to get to the Valve, but I did remove the L/F wheel, battery, Coolant bottle etc... and inner fender.
With all that out of the way, there is a plate bolted to the Frame with 2 bolts, and the P-Valve has 2 bolts that thread into the plate.
I soaked it down for a couple days with Kroil as every thing is pretty rusted.

First removed the Brake Lines from the Valve, then with an Impact gun the bolts took the plate right off the frame. Now with the Valve and Plate in hand made it easy to get the other 2 bolts off.
Wire wheeled off all the crusty rust, and a couple coats of POR to pretty it up. I first screwed in all the Brake lines, left them loose, then bolted the Valve to the Plate, and then the Plate to the Frame. After it was secured down, then tightened the Brake Lines.
Made sure I used Anti-Seiz on the bolts, for if there is a next time.

You will need to remove the Brake Line at the MC and plug it off so it isn`t draining it`s fluid every where.
I have some fittings I use. Made some double flair Brake Line, cut it off inch behind the fitting and mashed the end for a plug.

Here is what the valve looks like.

You will need this tool to bleed the brakes.
It keeps the valve inside centered.

I did some YT searching and came across 4 interesting one`s on the P-Valve.

This first one, the guy has disected one like was on my 86. Shows the little rubber seal that was leaking. It is on the rear fitting for the rear brakes.

This one guy is showing the new design, it has the rubber plug on the front end. Same leaky problem.


This one the guy disects a new style and shows a possible problem with the inner seal.


This final one shows the inner working of the valve.


One thing with the new Valve. The Brake Line from the Master Cylinder to the Valve for the rear brakes, is a larger thread size. So had to cut off the end of the line, and replace the fitting and redouble flair it.

Hope this helps some one.

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