Question about the location of the brake residual valve. - Vintage Mustang Forums
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Old 01-16-2006, 08:44 PM   #1 (permalink)
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I have the Cobra Auto front discs, MC and stock rear drums. All new lines, dist block and an adj prop valve.
The brakes have been great since I got it back on the road, it just has a little too much travel before engaging. I have an adj. MC rod and it's adjusted to just before the brake light comes on.

From alot of searching and reading I realize I didn't install a res. valve in the rear line.
Question is, where should it go? Does it have to go close to the MC or can I put it at the rear ahead of the flex line going to the axle?
The rear would be an easy install, the front would need a re-do of the line. Doesn't matter to me, I just want to install it where it will work!
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Old 01-16-2006, 09:17 PM   #2 (permalink)
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The residual check valve is located inside the master cyl.

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Old 01-17-2006, 04:21 AM   #3 (permalink)
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Agreed ... it's in the MC.
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Old 01-17-2006, 11:57 AM   #4 (permalink)
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Thanks for the replies, but the MC that Cobra Auto sells does not have a res valve in the body. It needs to be added to the rear line.
I bought a Wilwood 10 lb valve and it said to mount it near the MC, just wondering if it really matters where in line to install it.
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Old 01-17-2006, 12:38 PM   #5 (permalink)
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Quote:
Thanks for the replies, but the MC that Cobra Auto sells does not have a res valve in the body. It needs to be added to the rear line.
I bought a Wilwood 10 lb valve and it said to mount it near the MC, just wondering if it really matters where in line to install it.
It's just a check valve so it doesn't realy matter where it goes. The main reason for mouning neer the MC is for easy access and to check for leaks.
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Old 01-17-2006, 05:08 PM   #6 (permalink)
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I think you are mixing up a residual valve and proportioning valve. The residual valve holds a slight amount of pressure in the rear lines (13 psi?) to overcome the spring pressure that otherwise would delay engagement of the rear brake shoes. The proportioning valve will NOT hold pressure in the rear brake lines. It merely allocates fluid between front and rear brakes.

The residual valve is no more than a rubber seal looking piece which fits behind the seat in the master cylinder. If you pull off the brake line to the front reservoir, then thread a drywall screw part way into the seat, you can yank on the screw with pliers and remove the seat. Behind that is where this residual valve should be.

In my limited experience, most rebuilt master cylinders lack the residual valve. Don't know why, but they are simply missing. Once you install the residual valve, you can either install a new seat or take the old seat and use fine sandpaper 220 or finer, to take out the scratches and goobers made by the drywall screw. To install the seat, simply place it into the hole and press it LIGHTLY so that is alligned straight. Then, when you tighten down the flare nut on the brake line, it will seat the seat to the proper depth. Makes a nice tight joint.

For more on the difference between proportioning valves and residual valves, see the website for Master Power Brake Corp. They probably have the best technical discussion of these valves and their operation I have read in 10 years of the hobby.
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