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proportioning valve problems


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I went to bleed my brakes last night and ran into a problem. I bought the rebuild kit for my prop valve, and installed it. While I was bleeding my brakes I noticed I had leaks at the prop valve. One from the lower rear line, one from the bottom steel plug, and fluid was coming out of the brake light sensor. The leak at the light sensor thing, is that from not putting the top little seal in right? Should I even bother with this prop valve or try to find a new one? I bought all new brake lines! OEM pre bent.

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I would check the seal on the sensor. As for the brake line leak, it could be two things. One, the flare on the new line wasn't done correctly or is split. Two, the old connection dimpled the inside of the proportioning valve and the new line doesn't fit the old dimple. You might try loosening and re-tightening the fitting a few times to see if you can get them to conform to each other.

 

 

“If you can't explain it simply, you don't understand it well enough.”

--Albert Einstein

 

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Just to add that if you replaced the brake lines with stainless ones they are more difficult to seal. A new proportional valve is around $80.00 so might be worth replacing if you continue to have leaks from the sensor and bottom bolt.

-john

(jbojo)

351C 4V cc heads, 10.5 : 1 CR, 290 Herbert cam, Flat top forged pistons, forged connecting rods, Atomic efi,

C6 with Gear Vendor overdrive, 3.89 Tru Trac, Hooker Super Comp with 2 1/2" Pypes Exhaust.        

 

Some Mod pictures can be seen at: [button=http://www.7173mustangs.com/forum-garage?filterxt_uid=2026]Bojo's Garage[/button]

 

 

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they are not stainless. I found a prop valve at dallas mustang, so hopefully that will work. I'm going to take the old one out tonight. I'll let you know what I see. GRRRRR, so much for saving a couple bucks!!! PS; a little touch up paint is now required!!!

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they are not stainless. I found a prop valve at dallas mustang, so hopefully that will work. I'm going to take the old one out tonight. I'll let you know what I see. GRRRRR, so much for saving a couple bucks!!! PS; a little touch up paint is now required!!!

 

Yeah, I used stainless hoping to avoid the rusting issues but had a lot of leaking connections. They are all fixed now but I needed to do touch up on the frame because of the fluid too.

-john

(jbojo)

351C 4V cc heads, 10.5 : 1 CR, 290 Herbert cam, Flat top forged pistons, forged connecting rods, Atomic efi,

C6 with Gear Vendor overdrive, 3.89 Tru Trac, Hooker Super Comp with 2 1/2" Pypes Exhaust.        

 

Some Mod pictures can be seen at: [button=http://www.7173mustangs.com/forum-garage?filterxt_uid=2026]Bojo's Garage[/button]

 

 

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  • 1 year later...

I am in the same boat. Very Frustrating! I rebuilt mine using the musclecar research kit and seemed to fix the leaks at the bottom of the valve. Now I work on my car yesterday and find the switch plug in is full of fluid and dripping down my frame rail.

 

Do you guys clean the fluid off with brake cleaner, or what?

 

How are the reproduction proportioning valves? any problems? I hate the repop fuel sending unit I bought and the reproduction power steering hoses. They are nothing like the originals at the connection points.

 

kcmash

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I got the one from Dallas Mustang and it looks, fits and works like the original. I think it was labeled the 1970-1972 mustang prop valve.

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Here is some hopefully helpful info. I rebuilt my proportioning valve (been thru this stuff with 2 cars - a 71 & the other a 69), and I would say one thing that may have been missed above is that the plastic sensor switch that is in the prop valve should not be exposed to fluid. If fluid is coming out of the sensor switch, this means that there is a fixable, but internal leak in the prop valve.

 

There is a "shuttle valve" inside that moves back and forth if the front & rear hydraulic chambers are not producing balanced hydraulic pressure (note that bleeding brakes and not using a centering tool will also move the shuttle valve to one side). This shuttle valve has seals that should prevent fluid from entering the cavity where the switch is operating - even if one chamber has failed and the valve moves all the way to one side. So, if fluid is coming out of your switch, it's time to pull the prop valve, get a rebuild kit from musclecarresearch.com, and rebuild it. Most of these prop valves are completely rebuildable, and the kits are like $25 with great instructions. (Find out if your switch is good or not and if it comes with prop valve if you buy one because the sensor switches are like $25 each also)

 

I had a "hard luck day" rebuilding my prop valve which is documented here: http://www.7173mustangs.com/thread-rear-brake-issues-don-t-let-this-happen-to-you

Maybe there is some help in that if you can get thru reading it all.

 

The other leaks you mention are probably from the new lines. Fortunately, you bought OEM steel & not stainless as stainless is hard to get seated properly (mentioned above), but since they are new you are likely facing issues that the flares aren't seating properly because they are new. Loosen and retighten, maybe several times, but don't overtighten, as you can damage the line and or the seat. I would inspect the flares for splits like mentioned above, as no amount of tightening will ever seal a split.

 

Good luck!

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