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Old 04-15-2018, 09:03 PM   #1
Lawdogg298
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Vacuum lines for factory AC

Hey guys. I have been scouring the internet for help with vacuum lines and have so far come up empty. I will lay out my questions separately. Any help would be greatly appreciated.

Truck info: '71 K10 with 350 V8, Edelbrock 1406 carb, TH350 automatic trans. I bought the truck in "running condition" so the PO ran the lines. I recently installed a painless wiring harness and am now trying to piece together the last bit of factory AC

1. Currently all four Vacuum ports off the carb are used. Timed port to distributor, PCV port to PCV, Manifold Vacuum to trans, Power brake port to brakes. -- Where should I "T in" the vacuum hoses for AC/reservoir?

2. I have 2 vacuum lines starting off the master cylinder, running down the frame (see pictures). Top tube is fuel line. Middle one runs to the rear brake, but the bottom one is open to atmosphere. Where is that third line supposed to terminate?
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Old 04-15-2018, 09:13 PM   #2
B. W.
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Re: Vacuum lines for factory AC

1. Install a vacuum fitting in the manifold for the A/C line. I used a fitting with a small nipple for the A/C & a large (3/8) for the brake booster. P/N 302177, factory vette fitting.

2. the capped line looks like the fuel return line to the tank, if your pump is a two port pump you don't need it.
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Old 04-15-2018, 10:12 PM   #3
Lawdogg298
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Re: Vacuum lines for factory AC

Thanks for the reply. I went out to double check the lines after your post. The open line, on second inspection does not look attached to the brake booster/master cylinder. You were spot on. I missed a right angle whilst crawling under the truck.

The "brake booster" port comes off the back of the Edelbrock I'm using (im not running stock). So I should be able to use a "T" and bring out the AC vacuum line from that? Or should I install a new vacuum fitting for just the AC?

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Old 04-16-2018, 10:48 AM   #4
B. W.
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Re: Vacuum lines for factory AC

You can tee off of that. I think the stock port for the brakes is on the manifold behind the carb, that's why I ran mine there.
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Old 04-16-2018, 01:57 PM   #5
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Re: Vacuum lines for factory AC

It sure looks like your master is hooked up the combo valve backwards...
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Old 04-16-2018, 03:15 PM   #6
B. W.
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Re: Vacuum lines for factory AC

That's how mine's plumbed.
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Old 04-16-2018, 04:27 PM   #7
Andy4639
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Thumbs up Re: Vacuum lines for factory AC

Quote:
Lawdogg298,
. I have 2 vacuum lines starting off the master cylinder, running down the frame (see pictures). Top tube is fuel line. Middle one runs to the rear brake, but the bottom one is open to atmosphere. Where is that third line supposed to terminate?


I not sure if you meant to say vacuum lines are off the master cylinder are not but in any case. Your picture has the proportioning valve hooked up backwards. It needs to be rotated 180* The line coming straight out the back should be pointing toward the front of the truck and going to the front brakes.
The line coming out of the bottom should be going to the rear brakes.
The front brake lines can be either tee'd off at the frame are have their own line for each side. The rear brakes will be one line back to the rear end and then tee'd off for each wheel.
The line you are asking where it goes I think should be your gas tank vent line maybe.
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Get out and drive the truck this summer and have some fun!
It sucks not being able to hear!

LWB trucks rule, if you don't think so measure your SWB!
After talking to tech support at Air Lift I have found out that the kit I need is 60811. Per the measurements I gave them. Ride height of truck inside spring and inside diameter of springs.
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Old 04-16-2018, 05:10 PM   #8
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Re: Vacuum lines for factory AC

Quote:
Originally Posted by B. W. View Post
That's how mine's plumbed.
I'm confused, all of the instructions I see online show the front reservoir for the font brakes and rear for the rear. I believe those masters are for a disc/disc setup anyways so they reservoir and piston are the same size so it wouldn't matter.

But hey, if it works!
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Old 04-16-2018, 08:00 PM   #9
Lawdogg298
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Re: Vacuum lines for factory AC

Hey guys, thanks for all the replies.

The 2 lines in question do run to the brakes as you described, Andy. The open line is a vent. It takes a funny turn on the frame that I missed while i was upsidedown and underneath. I was actually looking at the wrong line... After B.W. raised that possibility last night, I rechecked everything. Guess I should double check before posting, to not look so foolish

I actually have a copy of the service manual for a 71. It looks correct to me, but im probably the least qualified here to make that determination. Picture is posted below.

Again, thanks for your comments. They have been a great help.
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Old 04-16-2018, 08:01 PM   #10
Andy4639
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Wink Re: Vacuum lines for factory AC

demian5,
After looking and checking google you are correct, it doesn't matter which way you hook the proportioning valve up. Google shows it either way.

I'm more worried about the vacuum lines coming off the master cylinder myself!
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1971 LWB Custom, 6.0LS & 4L80E, Speedhut.com GPS speedometer & gauges with A/C. 20" Boss 338's Grey wheels 4 wheel disc brakes. My Driver
Seeing the USA in a 71


Upstate SC GM Truck Club
2013,14 and 2016 Hot Rod Pour Tour


http://upstategmtrucks.com/



Get out and drive the truck this summer and have some fun!
It sucks not being able to hear!

LWB trucks rule, if you don't think so measure your SWB!
After talking to tech support at Air Lift I have found out that the kit I need is 60811. Per the measurements I gave them. Ride height of truck inside spring and inside diameter of springs.
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Old 04-16-2018, 08:19 PM   #11
Lawdogg298
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Re: Vacuum lines for factory AC

Ya, foot in mouth. I was talking about vaccum lines for the AC and then brake lines... apparently I just mashed them together. brake AC vacuum line? brACuum line? anyone?
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Old 04-16-2018, 08:32 PM   #12
Andy4639
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Thumbs up Re: Vacuum lines for factory AC

Quote:
Originally Posted by Lawdogg298 View Post
Ya, foot in mouth. I was talking about vaccum lines for the AC and then brake lines... apparently I just mashed them together. brake AC vacuum line? brACuum line? anyone?

Don't feel bad we all have done it. It just good humor to point out we are all human!
That line under the truck that wasn't hooked to anything probably was for the charcoal filter up front under the battery that ran back to the gas tank vent.
__________________
1971 LWB Custom, 6.0LS & 4L80E, Speedhut.com GPS speedometer & gauges with A/C. 20" Boss 338's Grey wheels 4 wheel disc brakes. My Driver
Seeing the USA in a 71


Upstate SC GM Truck Club
2013,14 and 2016 Hot Rod Pour Tour


http://upstategmtrucks.com/



Get out and drive the truck this summer and have some fun!
It sucks not being able to hear!

LWB trucks rule, if you don't think so measure your SWB!
After talking to tech support at Air Lift I have found out that the kit I need is 60811. Per the measurements I gave them. Ride height of truck inside spring and inside diameter of springs.
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Old 04-17-2018, 11:51 AM   #13
demian5
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Re: Vacuum lines for factory AC

Quote:
Originally Posted by Lawdogg298 View Post
I actually have a copy of the service manual for a 71. It looks correct to me, but im probably the least qualified here to make that determination. Picture is posted below.
Man, even more confused, it shows it connected both ways?!
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1986 C20 Scottsdale (grandpa truck)
1964 Impala SS
1959 Austin Healey 100-6 BN6
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Old 04-17-2018, 01:20 PM   #14
B. W.
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Re: Vacuum lines for factory AC

Yep, that's crazy! The 10 series is different than the 20/30 series. The pic I posted is an original '71 K20.
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