brake question?
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Junior User
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brake question?
Hey guys I know I've been posting a lot of stuff on my brake issues but I think I may have figured it out. I have replaced almost everything in system on a 78 f150. I just found that my mechanic had replaced my rear brake line and ran it straight from the mc bypassing proportioning valve although the front brakes still utilize the valve on the frame rail. And he npdidnt cap off the old line that are running into the valve so I'm guessing that is where air is getting into my system because I cannot get any peddle it just goes to the floor but will stop truck eventually. My question is can I cap off those inlet and outlet for the rwar on the valve or will that make the rear brakes lock up?
Hotshot
Joined: Apr 2009
Posts: 14,333
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From: Stanley, VA
The proportioning valve is there for a reason, the brake system isn't going to function properly without it, especially if only half of the valve is installed.
If your "mechanic" bypassed it because it wasn't working it needs to be replaced. If he bypassed it because he was lazy then it needs to be plumbed back into the system.
Right now, you're fighting yourself. Get the prop valve working, that may be your whole problem.
If your "mechanic" bypassed it because it wasn't working it needs to be replaced. If he bypassed it because he was lazy then it needs to be plumbed back into the system.
Right now, you're fighting yourself. Get the prop valve working, that may be your whole problem.
Moderator & parts slinger
Joined: Feb 2007
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From: S/W Missouri, Polk county
I'd get a new "mechanic" first off, and thump the old one in the head for being an idiot.
You need to connect the pro valve back in the system.
The pro valve is the "mixing unit" for the brake pressure and the back up emergency lock out system, if you have a front or rear brake line failure. Its the valve to still allow you to have either front or rear brakes, and how get a dash light indicating a failure.
Yes get a new one, good luck finding it, yours may be able to be cleaned up and the only problem is the internal piston is stuck......
You need to connect the pro valve back in the system.
The pro valve is the "mixing unit" for the brake pressure and the back up emergency lock out system, if you have a front or rear brake line failure. Its the valve to still allow you to have either front or rear brakes, and how get a dash light indicating a failure.
Yes get a new one, good luck finding it, yours may be able to be cleaned up and the only problem is the internal piston is stuck......
Hotshot
Joined: Apr 2009
Posts: 14,333
Likes: 247
From: Stanley, VA
, replace the prop valve and your so-called "mechanic".
Post Fiend
Joined: Mar 2011
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From: Lynchburg, VA
In the event of a loss in pressure in the front circuit, the primary cup directly contacts the secondary cup in order to apply pressure to the rear brakes. If the rear circuit loses pressure, the secondary cup bottoms out and allows the primary circuit to build pressure for the front brakes.
Post Fiend
Joined: Mar 2011
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From: Lynchburg, VA
And yes, slap your "mechanic" upside the head, demand your money back, and find a new mechanic.
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Moderator & parts slinger
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From: S/W Missouri, Polk county
That part you are calling a fitting is the proportional or (as Chilton & Ford call it) the differential brake valve. The Front Disc brakes take higher volume but less pressure of the fluid when it is applied to the system and account for about 65-70% of the stopping power and control in short distances on the vehicle.
The rear drum brakes take less volume and a higher pressure and tend to control more without overheating for long distance stopping. That is what this valve is for. To balance the disc brakes with the drum brakes.
Do I have my info correct now?
The rear drum brakes take less volume and a higher pressure and tend to control more without overheating for long distance stopping. That is what this valve is for. To balance the disc brakes with the drum brakes.
Do I have my info correct now?
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Thx guys for the replies I hooked up the pro valve the way it should be but still no pedal in fact can't hardly get any fluid to rear because pedal never gets hard. Do I need to bleed the pro valve with the bleeder rod or does it sound like its just bad?? Thank for your help guys I gotta figure this out and don't really want to take it to another mechanic. If you catch my drift lol
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