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  #1  
Old 02-19-2008, 09:13 AM
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Question '80 450SL - Help beginning evaluation of vacuum system

Yes, I turn to the forum for help again. So far, so good.

I have a 1980 450SL that runs great, no problems there. But from my understanding when it was checked out by a mechanic a few years back, there are a couple of vacuum leaks in the car. The main things that I have noticed are with the doors and trunk locks, but there may be other things I don't know about.

I have the shop manual, a couple of vacuum diagrams from online, and a MityVac, and what I'd like to do is go through and check the vacuum lines, find the leaks, and get everything back as it should be. But I'm not sure where or how to start.

1) How many vacuum systems are there in the car? I have heard references to a couple of different ones - basically one controlling the locks and one that controls the transmission, but I'm not sure if they are one and the same, or if they are separate systems.

2) I have also read numerous articles of folks who aren't able to get their car in reverse, to turn off, etc, because of vacuum leaks. I have NONE of these problems so far, and I'd like to keep it that way, so I'd like to avoid anything that may have adverse effects on these systems.

3) Does anyone have any advice on where or how to start, and exactly what I need to do to test the system?

Thanks in advance for any help!

Zack
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  #2  
Old 02-19-2008, 01:49 PM
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Down withe the flu and have some time ...

The basic setup for the locks is as follows:

Vacuum is drawn by a fitting at the back of the intake manifold. There is a combo fitting there. One line, secured by a banjo fitting runs down to the trans. Leave this one alone since your tranny is OK.

On top of that fitting, there should be a rubber hose that connects to a plastic line that runs over to the driver's side to a bunch of connectors near the hood hinge. You will notice a line that runs back across the firewall to va vacuum tank under the right fender.

There will also be a yellow line, which supplies the passenger door/trunk/gas locks (elements). This runs to a valve in the driver's door. The valve has connections for the "lock" and "unlock" side. When you turn the key to "lock" the valve applies vacuum to the lock side of the elements, and vice versa for unock. The lock/unlock of the driver's door is mechanical.

The two vacuum lines run from the valve in the driver's door to the pass. door, then to splitters, and to the trunk lock and gas door. The gas door may have only a "lock" side, with the unlock handled by a spring when the vacuum is released by the door switch.

All of the elements have rubber diaphragms that can crack and cause leaks. The valve in the driver's door can lose its seal. The fitting where the line enters the tank can dry out and leak.

I suggest that you start by removing the panel on the right side of the trunk. You should see where the lines from the pass. door branch to the rear elements. You can connect your mityvac and test both sides of all three elements. Lock has a red stripe; unlock a green. Connect the mityvac, pull a vacuum on both sides to what works.

Have fun!
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'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe

Last edited by ctaylor738; 02-24-2008 at 05:23 PM. Reason: Bad info on gas door lock
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  #3  
Old 02-19-2008, 04:16 PM
oso oso is offline
'87 300TD
 
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Central locking system leak...

would the same be applicable to 1987 300tdt?
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  #4  
Old 02-19-2008, 05:42 PM
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Sort of. I've never messed with an '87, but I think in '86 Mercedes started with an electric pump setup that runs one way for vacuum and the opposite for pressure, so there is only one line to each element.
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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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  #5  
Old 02-20-2008, 08:47 AM
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I have an 81 completely apart right now except for the vacuum lines, dash is off as well as doors, so if you "cant see" something , I may be able to help. I am amazed at how many lines go to and fro, simply amazing when you see it all exposed
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  #6  
Old 02-20-2008, 11:52 AM
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Probably the biggest potential for leaks on the '80 is the climate control II system. If the heater/AC works, it must not be leaking, but if it doesn't work properly, one can categorically state that there are vacuum leaks, most likely bad vacuum pods. Cycle the controls, see if all the air comes from the defrost vents (indicating bad pods elsewhere), if any air comes from the footwell vents (if not, bad footwell pod), if any comes from the AC vents, etc... Another potential leak area in the climate control II system is the servo area. There's a real ratsnest of tubing there. If the AC and/or fan doesn't come on, it's usually a leak that causes the vacuum switch not to operate to turn on the unit.
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  #7  
Old 02-20-2008, 02:10 PM
oso oso is offline
'87 300TD
 
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central locking system failure

Quote:
Originally Posted by ctaylor738 View Post
Sort of. I've never messed with an '87, but I think in '86 Mercedes started with an electric pump setup that runs one way for vacuum and the opposite for pressure, so there is only one line to each element.
I think you are right on the money here- I can hear the pump run somewhere underneath the rear seat maybe. It cuts off after 10 sec. or so. What is the 1,2,3,.. : from the electric vacuum pump to where?
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  #8  
Old 02-20-2008, 07:20 PM
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Cool, now what??

Awesome, thanks for that information.

Now I know this sounds like a stupid question, but how exactly do I do the test? Do I need to have the engine running or something, or do I just plug the MityVac into one end of the hose and start pumping?

Thanks!
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  #9  
Old 02-20-2008, 07:35 PM
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You basically connect the mityvac securely to one hose at a time using a length of rubber vacuum hose. Pump it up and watch the gauge. The vacuum element should do its thing, and then hold vacuum.

Example, open the fuel door, and connect to the lock line for the fuel door. Pump up the vacuum. You should see the little rod come out that would stick through the hole in the door, and then hold vacuum. Same for the unlock side, but the rod pulls back. If an element won't move or won't hold vacuum, it should be replaced.
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'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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Old 02-20-2008, 08:24 PM
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In a nutshell, from what I have learned from my 140.

The electric pump-based systems seem to have a single line running to each element from the pump. Sometimes there are multiple circuits, like one for the doors, and one for everything else.

There are also electrical switches in each lock lock or element. So for example, when you lock the driver's a circuit is closed (or opened) that tells the pump's control unit to apply suction to the lines to lock them. Same for unlock, except the pump runs the other way and produces pressure to move the elements to unlock.

So the drill is the same. Find the pump, find a place where you can hook up to individual elements, and exercise them with suction and pressure.

A little known fact is that a mityvac will produce pressure by through the vertical fitting generally covered by the little plastic cap. But unfortunately, the gauge only shows vacuum.

There are generally micro switches in each element that tells the control unit that the element has locked or unlocked. So if you lock the doors, and the control unit doesn't get a signal that the everything is in the lock position after, say, 10 seconds, it will shut the pump down. This is to prevent the pump from running continuously and frying itself.
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Chuck Taylor
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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  #11  
Old 02-21-2008, 12:29 AM
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I am scared to ask anything. Can I just buy a mini vaccume and plug it in the cig lighter and attach it for when I drive my car? :0)
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  #12  
Old 02-21-2008, 09:11 AM
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if you mean to control vacuum to close flaps, no, its a closed system, you would have to have a line in and out
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2011 Porsche Cayman - Bond,James Bond
99 E320 THE Queen Mary
62 220b - Dolly - Finally my Finny!
72 450SL, Pearl-SOLD
16 F350 6.7 Diesel -THOR
07 Lexus RX 350 - Lexi
14 38HP John Deere 3038E Tractor -Mean Green
84 300SD, Benjamin -SOLD
71 220 - W115-Libby ( my first love) -SOLD
73 280 - W114 "Organspende" Rest in Peace
81 380 SL - Rest in Peace
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Old 02-21-2008, 10:55 AM
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Ok, so I tried this out last night. I went to my gas door and plugged it in to the yellow line with a red line on it. when I pumped the MityVac, I got absolutely nothing. No reading on the gauge, nothing.

So can I assume that either there is a leak in the line somewhere, or that the vacuum pod is not working?

Keep in mind the car had been off for a little bit, and I did not turn it on when I tried it.

Thanks!
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  #14  
Old 02-21-2008, 11:15 PM
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Correct, assuming that when you put your finger over the MV and pumped it, you got a reading.
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'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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  #15  
Old 02-22-2008, 11:23 AM
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So Here's what I found out...

So I went and started playing around with my vacuum system last night, and per your advice, I started in the trunk area. I noticed a few things that I'm not sure are correct or not, so this is kind of like a choose-your-own-adventure book

I started off with the gas tank door. When I took it apart, there was only one vacuum hose going into it - it was the yellow hose with red stripe. I could see the trunk lock hoses running underneath it, and I noticed that there were two: The Yellow and (Red and Green). When I looked a little bit down the line, I saw that the Y/R line split in two before, right before the gas door (one for the gas door and one for the trunk), but there was no split anywhere in the Y/G line.

So here's my first question:

1)Are there supposed to be two vacuum lines running into the gas door vacuum pod? A Y/R and a Y/G? There were two nipples on the pod, but there was no sign of a Y/G.

Anyways, when I tried the vacuum directly to the pod, it worked fine, but when I put the vacuum on the line itself, I got nothing, so I figured the leak had to bed somewhere before there. The next thing I did was take the glovebox out and looked at the lines there, before they split off into the door.
When I tested the vacuum between that point and the rear elements, I was able to hold a vacuum, but when I tested the line coming from the engine, I was not able to get any reading.

2. Can I assume then that the leak has to be somewhere either in the driver's door or under the hood where they all split off?

So when I looked under the hood, where all of the vacuum hoses go into connectors right before they go through the firewall, I did notice that one of the Y connectors had a nice little tear in it.

C. Without knowing more than that, is there a fair chance that my entire problem stems from that bad connector?

Anyways, I hope I'm at least somewhere close to the answer.

Thanks!
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