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  #1  
Old 08-26-2007, 03:09 AM
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Vacuum line to power brake booster: bad valve?

While diagnosing a problem with the vacuum pump I tested the main vacuum line to the booster by disconnecting the line at the booster and connecting my hand pump there. I was able to generate a vacuum in the door lock circuit (via the connection from the booster line) by pumping from the nut where the line connects to the booster.

I'm not too sure about how the valve in the booster line works; am I supposed to be able to pull air out of the door lock circuit, through the valve, back in the direction of the booster? It seems the valve is there to keep this from occurring.

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  #2  
Old 08-26-2007, 08:48 AM
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No. Vacuum is created in the booster directly from the main line off the pump, to the booster. If you want to test the booster, pull a vaccum on the main line.
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  #3  
Old 08-26-2007, 11:26 AM
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Thanks for the reply. From the looks of your answer I'm not quite sure if I've explained my question correctly (perhaps a moratorium on posts at 3 AM is in order?).

I was trying to test the booster line itself, to see if it would hold a vacuum. So I broke the connection at the booster and connected my pump to the line there. (This is where I think I might have been unclear; did my first post sound like I was trying to test the booster?) What I noticed when I started pumping is that I was able to draw air through the valve in the line, away from the vacuum pump and the door lock circuit.

Seems like the valve should be trying to maintain vacuum in the booster instead of letting vacuum out, back toward the pump. I'm trying to figure out if this is how it should work before putting down some money on a replacement line.

Sorry for the length. Apparently I like to see myself type.
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Old 08-26-2007, 11:30 AM
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Not sure how that valve works but here is the best way to check that part of the vac system. One the main vac line from the vac pump to the break booster, put your mity vac on the same barb you did before. Plug any other barbs that stick out. Also make sure the main vac lineis tightly bolted to the break booster. Then start the car and read the vac on the gauge. If it reads 20"-25" then your vac pump and booster are fine. If it is low than one of the two is leaking. Next unbolt the line from the break booster, then seal the end of the line, I usually lick my thumb and cover the hole tightly. Start the car again. If it reads low now then your vac pump is bad. If it reads 20"-25" then the booster is leaking.
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Old 08-26-2007, 01:53 PM
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It's got to let vacuum into the door lock line, there's no other place to get it. (if I understand the question correctly).
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1977 300d 70k--sold 08
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1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
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1982 Bluebird Wanderlodge CAT 3208--Sold 2/13
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  #6  
Old 08-26-2007, 04:02 PM
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Quote:
Originally Posted by Biodiesel300TD View Post
Not sure how that valve works but here is the best way to check that part of the vac system. One the main vac line from the vac pump to the break booster, put your mity vac on the same barb you did before. Plug any other barbs that stick out. Also make sure the main vac lineis tightly bolted to the break booster. Then start the car and read the vac on the gauge. If it reads 20"-25" then your vac pump and booster are fine. If it is low than one of the two is leaking. Next unbolt the line from the break booster, then seal the end of the line, I usually lick my thumb and cover the hole tightly. Start the car again. If it reads low now then your vac pump is bad. If it reads 20"-25" then the booster is leaking.
Thanks for the procedure. I'm fairly certain (like, around 99.314159264% sure) my pump's in need of repair (no power brakes, no action at the shutoff valve, no vacuum pressure at the barb you mention, oil in the air filter, &tc.), but I'll try it because why not.

Quote:
Originally Posted by kerry edwards View Post
It's got to let vacuum into the door lock line, there's no other place to get it. (if I understand the question correctly).
I guess part of the problem is that there a variety of booster line configurations. I've attached a simple diagram of mine. I connected my pump at point A and was able to generate a vacuum at point B. I know the engine pump should be able to draw air from point A to B. But should I be able to draw air from point B to point A with that valve in the way? I hope this helps clear up my question.

Thanks all for sticking with me.
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Vacuum line to power brake booster: bad valve?-mainline.png  
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  #7  
Old 08-30-2007, 09:17 PM
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For the curious...

The check valve on the booster vacuum line should not allow air to flow toward the booster, or vacuum to flow away from it. Got a new booster line; without connecting it to anything, I am able to generate 25 in Hg when I pump from the booster connection point.

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