Moving valve cover vac for brake boost

[keymonkey]

Hello all,
I'm installing a vac brake booster and I need a vacuum connection. The typical one listed in the instructions is being routed by copper pipe over to the oil fill cap on my driver side valve cover. I'm wondering if I should split that rear intake connection to also connect the booster, or if I should reroute the valve cover line over to the now capped pvc port on the pass side of my Holley carb leaving the intake one dedicated to the boost.

 

[Oleguy 74]

you need manifold vac.use capped port on carb

 

[SHX669]

Which Holley carb do you have ? My Holley.TA has a big vacuum outlet on the back that goes to the booster and a smaller one on the passenger side front that goes to my PCV .

 

[B RON CO]

Hi, you need a large vacuum port for the power brakes.
It is 3/8 line (I think).
Do you have a place on the intake manifold to tap into? A small port on the carb will not work, and you cannot share anything with the PCV system.
Good luck

 

[75MIKE]

https://classicbroncos.com/forums/showthread.php?t=307772

 

[keymonkey]

I have two large hose barbs. One on the rear of the intake manafold(where the valve cover fill cap is connected) and the currently capped off portnon the rear of my carb. https://imgur.com/gallery/ZfErE6C

 

[keymonkey]

Which Holley carb do you have ? My Holley.TA has a big vacuum outlet on the back that goes to the booster and a smaller one on the passenger side front that goes to my PCV .

Not sure model, but it does have a port onbthe rear pass side

https://imgur.com/gallery/ZfErE6C

 

[gr8scott]

Does the oil fill cap on the driver side have a PCV valve in it? (kind of look like it does).

Looks like two choices to me.

1. Run a long enough length of hose from the vacuum booster to the pass. side port that's currently plugged.

2. Cut the copper pipe just after where its attached to the valve cover and run a short length of hose from the copper pipe to the pass. side port.
Then use the rear port for the vacuum booster.

If the oil fill cap has a PCV valve in it, and it is really connected to the intake manifold, you need to go with option 2. Its not good to run
a PCV valve to an intake runner, as it could cause one cylinder to run lean. If it doesn't have a PCV valve in it then you need one. I'm
guessing the 1/2" hose coming off the breather on the pass side valve cover goes to the base of the air filter as the fresh air intake.

Edit: Can you post one more pic looking at the back of the carb?

 

[jckkys]

There a needs to be a 5/8" nipple on the bottom of the air cleaner to accept the S shaped hose (also 5/8"). Is there one? That's called a breather.

 

[keymonkey]

Does the oil fill cap on the driver side have a PCV valve in it? (kind of look like it does).

Looks like two choices to me.

1. Run a long enough length of hose from the vacuum booster to the pass. side port that's currently plugged.

2. Cut the copper pipe just after where its attached to the valve cover and run a short length of hose from the copper pipe to the pass. side port.
Then use the rear port for the vacuum booster.

If the oil fill cap has a PCV valve in it, and it is really connected to the intake manifold, you need to go with option 2. Its not good to run
a PCV valve to an intake runner, as it could cause one cylinder to run lean. If it doesn't have a PCV valve in it then you need one. I'm
guessing the 1/2" hose coming off the breather on the pass side valve cover goes to the base of the air filter as the fresh air intake.

Edit: Can you post one more pic looking at the back of the carb?

There is a pcv valve on the oil cap and the breather 1/2" does indeed go to the bottom of the air filter housing. Thanks....I ended up cutting the copper and running it into the rear of the carb. Then I ran the booster to the back of the intake manafold.

 

[jckkys]

You couldn't find a more complicated way to handle the PVC, breather, and brake booster plumbing. Most of the problem came when someone thought finned aluminum valve covers would be an improvement. They weren't. There are parts that work with these valve covers but they weren't used. Here :https://www.dennis-carpenter.com/en...kcase/c7az-6a892-a-pvc-grommet-in-valve-cover is a PCV grommet made to screw into the oil filler cap hole. Then get a PCV valve with a 90 degree 3/8" connection; https://www.fram.com/parts-search/FV202. A 4" hose that's 3/8" inside diameter needs to connect the PCV stuck in the grommet to the 3/8" nipple on the side of the Holley. This eliminates the need for the long 3/8" steel tube and the chrome oil filler cap. The 3/8" nipple behind the carb IS the brake booster location. It's not for PCV. You still need a breather to get clean air from the air cleaner into the crankcase. That's why I asked about a 5/8 nipple on the air cleaner so clean air is available. We need to see the bottom of the air cleaner.

 

[keymonkey]

You couldn't find a more complicated way to handle the PVC, breather, and brake booster plumbing. Most of the problem came when someone thought finned aluminum valve covers would be an improvement. They weren't. There are parts that work with these valve covers but they weren't used. Here :https://www.dennis-carpenter.com/en...kcase/c7az-6a892-a-pvc-grommet-in-valve-cover is a PCV grommet made to screw into the oil filler cap hole. Then get a PCV valve with a 90 degree 3/8" connection; https://www.fram.com/parts-search/FV202. A 4" hose that's 3/8" inside diameter needs to connect the PCV stuck in the grommet to the 3/8" nipple on the side of the Holley. This eliminates the need for the long 3/8" steel tube and the chrome oil filler cap. The 3/8" nipple behind the carb IS the brake booster location. It's not for PCV. You still need a breather to get clean air from the air cleaner into the crankcase. That's why I asked about a 5/8 nipple on the air cleaner so clean air is available. We need to see the bottom of the air cleaner.

Here is my setup now.

https://imgur.com/a/w6ZBIRw

 

[gr8scott]

Looks good keymonkey. How does the booster feel?

 

[keymonkey]

Looks good keymonkey. How does the booster feel?

A little spongy....still need to bleed the system. ;D On the schedule for this weekend.

 

[73azbronco]

copper pipe still confuses me, never seen copper, they do make a special vacuum hose.

 

[jckkys]

The copper tube is shorter in the last photo, but it still serves no purpose. Neither does the chrome oil filler cap. The rubber PCV grommet I referenced in post #11 does the same job. By putting the PCV currently in the front black oil filler cap into the rubber grommet and a breather elbow into that spot, a 5/8" hose that can be run to the nipple on the air cleaner.
The steel tube used on '76/'77 brake boosters can simplify and shorten the vacuum hose that is now sourced correctly behind the carb. Here;https://shop.broncograveyard.com/Brake-Booster-Vacuum-Line/productinfo/12503A/

 

[gr8scott]

So jckkys, what you're saying is that the pcv valve he has in the oil fill cap on the driver side doesn't function properly as a pcv valve? I'm not familiar with those caps.

 

[keymonkey]

copper pipe still confuses me, never seen copper, they do make a special vacuum hose.

Probably just buy a length of the same hose as the booster, but for now it seems to do the trick....the weird thing is there are hooked tabs on the Valve cover bolts that grab that copper..like it was stock.

 

[keymonkey]

The copper tube is shorter in the last photo, but it still serves no purpose. Neither does the chrome oil filler cap. The rubber PCV grommet I referenced in post #11 does the same job. By putting the PCV currently in the front black oil filler cap into the rubber grommet and a breather elbow into that spot, a 5/8" hose that can be run to the nipple on the air cleaner.
The steel tube used on '76/'77 brake boosters can simplify and shorten the vacuum hose that is now sourced correctly behind the carb. Here;https://shop.broncograveyard.com/Brake-Booster-Vacuum-Line/productinfo/12503A/

I'm also confused...the oil fill cap has a grommit and a PVC valve in it..the 5/8 hose transitions to copper as it was on hand, then transitions back to hose before hooking to the vac inlet on the carb.

The chrome breather is connected to the bottom of the air cleaner.

And the boost vac tube goes to the manafold behind the carb.

Am I missing something?

 

[gr8scott]

Am I missing something?

No, you're good.