Vacuum to Brake Booster & PCV Valve

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Vacuum to Brake Booster & PCV Valve

Postby jor on Sun Oct 31, 2004 9:47 am

67 F-100, 352, 2bl
I posted this before but I can't remember if it was here or on FTE. No one answered so I'll try it again. I replaced my 2bl  carb with a like model but the replacement did not have the vacuum port on the back like the other one did. That port was used to provide vacuum to the PCV valve.

The other vacuum source on my 352 comes from the intake manifold. That one provides vacuum to the brake booster. Anyhow, in order provide vacuum to the PCV valve, I T'd the line from the intake so that I could share the same vacuum source between the PCV and the booster. No deal. The power brakes quit operating.

Now, I have the single source back to the booster and the brakes work fine but the PCV valve is not longer functioning. How do I get vacuum to the PCV valve? Thanks.
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re: Vacuum to Brake Booster & PCV Valve

Postby heep70 on Sun Oct 31, 2004 10:00 am

Mine runs to and connects underneath the aircleaner.
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re: Vacuum to Brake Booster & PCV Valve

Postby 1968_ONEHUN on Sun Oct 31, 2004 11:54 am

your booster needs a vac.  line of its own to run off.You should have an outlet at the rear of the manifold for it.check to see if their is something there,possibly sealed of with a plug.you can buy the conector thats screws into the manifold for the booster vac. line to hook up to.hope these replys help.
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re: Vacuum to Brake Booster & PCV Valve

Postby jor on Mon Nov 01, 2004 10:31 am

Heep & 1968,
  I am using the intacke manifold vac (behind the carb) for the booster and it works fine. My question is, where can I get a source for the PCV? I'll check again for a plug and post. I just thought someone else may have experienced this same situation. Thanks.
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re: Vacuum to Brake Booster & PCV Valve

Postby heep70 on Mon Nov 01, 2004 11:23 am

The hose I was talking about prior was the PCV hose, just the wrong one.  It was the intake side.  My hose that runs from the PCV connects to the front of my carb.  Sorry for the bad info.  

What about a spacer plate.  I can't remember, but I think they had a stock spacer plate with that connection.  Its been many years since I had my FE.  I run a 460 w/ a Edelbrock carb.  Everything is different.  

There might be another vac port on one of the runners on the intake.  I am not sure if would run right going that way.  

Hang in there, I am sure somebody here has an answer for you that contains less BS.
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re: Vacuum to Brake Booster & PCV Valve

Postby willowbilly3 on Tue Nov 02, 2004 3:55 am

Sounds typical of a reman carb. Are you running any kind of spacer plate now? There are some that do have that port on them and that is what you will need, or else get the right carb.
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re: Vacuum to Brake Booster & PCV Valve

Postby willowbilly3 on Thu Nov 04, 2004 8:23 pm

Prior to PCV valves most cars had a road draft tube. On the FE it came out the back of the intake and went town to about the bottom of the engine. Most were about 1 1/4 inch diameter. You can use a valve cover breather but it will be an oily mess as the fumes contain some oil vapors. A PCV system has 2 sides. The side with the valve and suction, or vacuum. Then the vent side which is the hose from the valve cover to the air cleaner with a little foam element in it on the inside of the valve cover. This is the side that lets air in and under full throttle or heavy loads lets the excess crankcase capors out. On a tired engine with lots of blowby the vent gets nasty and you see oil in the air cleaner. On  most FE engines with a PCV system the vent hose goes into the oil cap.
PCV valves have a metered orifice in them and don't just let full vacuum open to the crankcase. They do have a very light spring that the vacuum has to overcome to unseat the valve. With out the valve gas fumes can enter the crank case. I personally witnessed a home made system with no valve, blow the oilpan and valve covers off a 283 when it backfired on start up and ignited the gas vapors that had went into the crankcase.
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re: Vacuum to Brake Booster & PCV Valve

Postby tcb1969 on Thu Nov 04, 2004 11:12 pm

When  you say "homemade system without the valve" I assume you mean the hose was still in place to the carb or air cleaner but the PCV valve was removed.  In that case - the vacuum could reverse - such as a backfire - and pull raw gas into the crankcase - creating the situation you mention.  

You are dead right about the oil - I run open breathers on my 70 mustang and I have to clean the breathers constantly.  But I swear the thing hauls butt better without recirculating the oil vapors.

The draft tube worked on the venturi principle - like a sandblaster - if you pass airflow over an opening it will create a vacuum in the opening - therefore pulling the vapors out of the valve covers - right into the air we breathe.  The PCV does the same function - but burns any unburned hydrocarbons by venting thru the carb.  

It's really a preference thing.  I like a clean, uncluttered engine bay - so I ditch all the hoses I can- legally - that's why I only own cars pre-1974.

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re: Vacuum to Brake Booster & PCV Valve

Postby jor on Fri Nov 05, 2004 9:05 am

Thanks for all the info. As is usually the case, there's more to this than I originally thought. I'll post when I pick and implement a solution.
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re: Vacuum to Brake Booster & PCV Valve

Postby FORDification on Mon Nov 15, 2004 1:39 am

Maybe this will help a bit...since a picture's almost always worth 1000 words, right? ;)

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re: Vacuum to Brake Booster & PCV Valve

Postby joethomas on Thu Sep 11, 2008 2:15 pm

Im still confused if the PCV valve is still required. My 1968 360 has a hose that runs from the valve cover pcv to the carb base plate ( just like the picture posted in this message). I have installed chrome valve covers and would like to do without the PCV valve. Can I replace the PCV valve with a breather cap and plug the carb base plate opening without damaging the engine.

Thanks for your help.
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re: Vacuum to Brake Booster & PCV Valve

Postby rubiranch on Thu Sep 11, 2008 11:29 pm

Yes, your engine needs a PCV valve.

It "draws" fresh air through a breather element (small filter inside air filter housing) and pulls combustion
bypass gasses (HC, hydrocarbons) and condensation from inside the engine crankcase.

This will increase the longevity of the oil in your engine by removing unwanted and unburnt fuel from the oil.  The PCV valve should be connected to a vacuum source under the carb rather than in an intake runner like the vacuum source for the power brake booster.

When I installed a Holley on my truck the carb did not have a fitting to provide a vacuum source for the PCV valve so this is what I did.

Image
I drilled a hole in the back of this spacer and cut the two slots in the throttle bores of the spacer to provide vacuum to the hole for the PCV valve.

Image
I then took float bowl vent tube out of the float bowl of a factory Holley for a 84 460 (any type of fitting will work I just had quite a few of these) and glued it into place.

Image
With the carb and spacer installed you can see the fitting.  You can also see the vacuum hose for the power brake booster.

Image
Here it is finished.

Ford first used a PCV valve in 1961.  Previously they used a "road draft tube" as mentioned before.  The reason for the road draft tube was as the vehicle traveled down the road the air passing the tube created a low pressure and fresh air wound go through a wire mesh filter inside the oil filler cap and provide the same function as a PCV system does.

:fr:
Last edited by rubiranch on Fri Sep 12, 2008 10:41 am, edited 2 times in total.
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Re: re: Vacuum to Brake Booster & PCV Valve

Postby rubiranch on Thu Sep 11, 2008 11:34 pm

joethomas wrote:Im still confused if the PCV valve is still required. My 1968 360 has a hose that runs from the valve cover pcv to the carb base plate ( just like the picture posted in this message). I have installed chrome valve covers and would like to do without the PCV valve. Can I replace the PCV valve with a breather cap and plug the carb base plate opening without damaging the engine.

Thanks for your help.


The crankcase builds pressure from combustion bypassing the rings.  With out a PCV system you will have small amounts of oil blowing out of the oil filler caps and that wont look very nice on your new chrome valve covers.

:fr:
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