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Old 11-15-2006, 01:25 PM
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Join Date: Oct 2006
Posts: 26
Still can't find vacuum leak...any help?

O.K. it has been 3 days now of looking and trying to find vacuum leak. '84 300TD
Won't shut off.
Door locks don't work.
Every thing worked fine before I adjusted the valves. I've looked at every connection that I might have pull off or dislodged. I had to replace the vacuum line that goes from the back of the exhaust manifold to what looks like a diaphram near the IP. The broke because it was brittle. I could only find soft tubing to replace it with. Nobody had the hard plastic line that broke. It connects to a banjo fitting off the manifold. Could this be the problem??? If I have to buy a vacuum gauge, does it have to a mityvac? And how do you use it to test for a leak?
I'M GOING CRAZY WITH THIS...p.s. my wife says she can hear hissing inside the driver's door. I took the door panel off and everything seems fine and of course I didn't hear any hissing. Does the master door switch ever go bad? The white plastic piece with the 3 vacuum connections. It looked brand new. Thanks people...

'84 300TD 100 % Biodiesel
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Old 11-15-2006, 02:06 PM
rrgrassi's Avatar
mmmmmm Diesel...
Join Date: Jun 2006
Location: Royse City Tx
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Did you check all the vacuum connections at the black box on the valve cover? Sounds like something is either still disconnected, or connected wrong. How are the brakes? If brakes are good, then you know the vacuum pump and brake booster are good. Check all connections, including the one coming out of the main line that runs to the brake booster. The vacuum connectors on that can be broken also.

Yes, the master lock actuator does go out, but it is highly unlikely that happened since it all worked prior to the valve adustment.

The hard brittle line that broke is actually not a vacuum line, but a line that sends turbo boost pressure signals to the ALDA. It is attached to the intake. It is supposed to go to a turbo switch over valve located on the firewall just up and left from the brake booster, then on to the ALDA.

You do not have to buy the Mity Vac brand name, but it does seem to be the best out there. The Mity Vac will

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Old 11-15-2006, 02:07 PM
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Gotta another one...
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Location: NE Ohio
Posts: 1,685
Buy a mity vac (I own a generic one I bought for $15 @ harbor freight), a set of golf tees, some electrical tape, and PM me when you get this stuff. I'll give you my number, and walk you through it.
1989 300E 144K
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Old 11-15-2006, 02:09 PM
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Location: Albany, OR
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If you are chasing vac leaks you really need a mity vac. You don't have to get that specific brand, but any vacuum hand pump with a guage will work.

To use the vac gauge you hook it up to a vac line and either start the engine and see how much vac the engine is pulling, or you can hand pump it and see if something is holding vac.

Master door switches don't usually go bad.

If the hard plasitc line broke right at the banjo bolt you can heat up the end of the line with a lighter and get it soft and them shove it on the banjo bolt quickly and it will be good as new.
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Old 11-15-2006, 02:10 PM
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Gotta another one...
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By the way, it's TOTALLY pointless to tackle anything like this on these cars without a hand vac pump. The leaks aren't really visible. I think autozone loans these, also.
1989 300E 144K
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Old 11-15-2006, 05:03 PM
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mityvac sources:

AZ (cheapest) $29.99
Harbor Freight $34.99 was on sale $28.99
NAPA $35.99

Might as well get one if you own a D or an older MB. Easy to use... you'll figure it out...
the sooner you start... the sooner you'll get done If it ain't broke, don't fix it.. Its always simpler to tell the truth...
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Old 11-15-2006, 06:14 PM
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Location: Metro Detroit, Michigan
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Vacuum Pump

Originally Posted by tobybul View Post
mityvac sources:

AZ (cheapest) $29.99
Harbor Freight $34.99 was on sale $28.99
NAPA $35.99

Might as well get one if you own a D or an older MB. Easy to use... you'll figure it out...

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Old 11-15-2006, 06:46 PM
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Block off every system except the shut off valve until you get it fixed and at least you won't have to open the hood to shut if off.
1977 300d 70k--sold 08
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Old 11-16-2006, 06:54 AM
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You could hook it up to a smoke machine if you know someone who has one. That's the easiest way by far.
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Old 11-16-2006, 07:21 AM
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Join Date: Feb 2005
Location: Cornwall UK
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it really is just a slow process of elimination, start with nothing attached and add bits till it stops working, that is unless the vacuum pump is knackered, but your brakes would be rubbish, the flexi pipe you put isn't collapsing under vacuum?
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Old 11-16-2006, 09:19 AM
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Join Date: Oct 2006
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No, the soft tube does not cllapse. BUT I THINK I FOUND IT. Master control switch in the driver's door. You can hear it leak. Part is on order...

'84 300TD 100 % Biodiesel
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