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  #1  
Old 06-05-2016, 01:55 PM
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vac lines help

Hi guys,
84 300sd .
the whole vaccum system is destroyed, the car is a total beater car.

i just need to know what is Bare Essential in the Vac system, no climate control, or fancy stuff,

i figured out how the IP shuts off, i think i can handle that.

transmission has a vac line . not sure what to do with it also? i would like it to shift properly it shifts real crappy
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  #2  
Old 06-05-2016, 02:04 PM
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Trevor Hadlington
 
Join Date: May 2014
Location: Worcestershire in England
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Will this help.
Attached Thumbnails
vac lines help-w123vacdoorlockdiag_cghj564684.jpg  
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  #3  
Old 06-05-2016, 02:17 PM
Shadetree
 
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I tried the easy way out but alas, this is the easy way out. Read the thread, hit and read all the links and be patient with yourself.

It's CRITICAL... how you set your transmission's vacuum system on your diesel MBZ...
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  #4  
Old 06-05-2016, 02:20 PM
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thank u for the quick response i appreciate it

also the switch over valves i think thats what they are. on top of the valve cover are destroyed also
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  #5  
Old 06-05-2016, 06:02 PM
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It's hard to tell with a vague description of "destroyed". Necessary vacuum lines include brake, transmission and fuel shut-off. The vacuum valves on the valve cover are for EGR.

The previously posted diagram is for a W123, which has a different vacuum set up. The W126 has a separate vacuum pump in the trunk for door locks.
I think the better question might be "What problems are you having?".
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  #6  
Old 06-05-2016, 06:06 PM
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Transmission shifting hard is usually a sign of a vacuum leak. Either a rubber flex fitting or the small black cap on the modulator are the first suspects.
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  #7  
Old 06-05-2016, 07:04 PM
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Is your vacuum system intact, but leaking, or completely messed up?

If its the first, don't panic, its likely not as bad as it looks. First, start with your engine bay. I suggest getting some new rubber hose (probably 3 meters or so), and either an assortment of cheap plastic vacuum fittings of the appropriate size, or buy the correct MB vacuum fittings (count what you have, buy those). The important thing is to be methodical. Take many more pictures of the vacuum system than you think you will need. Then take some more. Now you can start replacing hoses and fittings. Replace exactly ONE hose or fitting at a time. Keep doing this until you have no old hoses or fittings. Inspect your hard lines as you go. If you find a hole or crack, its fine to cut the hard line and splice it together with rubber hose. Typically your engine bay is the most degraded area.

Now if everything works, walk away and enjoy the frosty beverage of your choice. If not, its time to start troubleshooting. Invest in a hand held vacuum pump with a gauge and start looking for leaks. If your door lock system is disconnected from your engine, you can skip that for now. The first thing I would try is isolating the system to your HVAC. (On a w123 I believe it is a green/yellow line that passes through to the cabin. Try to pull a vacuum on that with the hand pump, if it holds, try cycling through all of the heat & air settings. This will help you narrow down what circuits are leaking. If you dont care about the hvac, just cap the line that leads to the system.

If your system is truly chopped up, I wish you the best of luck. I have not found a very clear diagram for my car, hopefully you can.
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  #8  
Old 06-05-2016, 08:27 PM
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this 300sd has been abused to hell and back and its refuesed to die !! i want to breathe some life into it, the motor is still good, it would be a shame to scrap this car.
i rebuilt a motor mount (all new rubber vulcanized), rebuilt the thermostat housing (aluminum welded and grinded) , the PO had the trunk full of water bottles, he would fill it up to go buy beer, refill exiting the store to go back home.
retightened the belts, they where soo loose it would barely spin the alternator(the threads where soo rusted it wouldnt budge),
i changed the oil and oil filter 8 quarts !!!
i want her for a shop car, beer run car, beater car.

now i need to get the vac system working to BARE ESSENTIALS, IP shutoff, Transmission. the AC and other stuff i will never care about







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  #9  
Old 06-05-2016, 11:15 PM
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on a good note, i got her shutting of when i turn the key off ! and instantly !

also shes a ether only starter...
i pulled 2 glow plugs wich are a complete Biatch ! and they dont work when connected to a batt, soo ill be getting some plugs in her and see if she can start on her own , god knows shes had a lot of ether over the years from PO
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  #10  
Old 06-05-2016, 11:34 PM
Shadetree
 
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I strongly recommend you adjust the valves and change the fuel filters. Those two fixes and a good set of glow plugs should make the engine start fairly well.

Don't use starter fluid if your glow plugs are working correctly. There's a good chance you can destroy the engine.
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  #11  
Old 06-05-2016, 11:55 PM
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Quote:
Originally Posted by Clemson88 View Post
I strongly recommend you adjust the valves and change the fuel filters. Those two fixes and a good set of glow plugs should make the engine start fairly well.

Don't use starter fluid if your glow plugs are working correctly. There's a good chance you can destroy the engine.
yeah i hate the idea of using starting fluid , but wont start any other way. ill get the glow plugs in and fuel filters and then if no go ill see about the valves since i cant do that

she will start all day long by her self after the first start with ether
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  #12  
Old 06-06-2016, 02:01 AM
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A diagram has been posted many times that shows which vacuum components are for the EGR system. If you remove those, that simplifies about half. I recall the valve cover vac switches are only for EGR. The tranny vac is to simulate the intake vacuum of a gasoline car, and there are many posts on that.
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  #13  
Old 06-06-2016, 08:51 AM
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The tranny does not use vacuum for upshifts; it should upshift smoothly even if the plastic line from the VAV is not attached to the vac modulator in the tranny. You need vac for downshifts only; without vac it will downshift but with a clunk.
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  #14  
Old 06-06-2016, 09:40 AM
Shadetree
 
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Quote:
Originally Posted by tyl604 View Post
The tranny does not use vacuum for upshifts; it should upshift smoothly even if the plastic line from the VAV is not attached to the vac modulator in the tranny. You need vac for downshifts only; without vac it will downshift but with a clunk.
No sir. I apologize if I may be mistaken for one who is contentious but that is not my understanding of the vac system on a 1984 300 SD Mercedes and it's relationship and interactions with the factory installed transmission.

Hard up-shifts are typical when the 84 SD has no vacuum supply or the vac supply is open and vacuum is lost. The lower the vac the harder the up-shifts.

It is my understanding that when this particular transmission has no vac supply it performs as if the engine is under extreme acceleration and reacts by shifting fast and hard.

The archives on this forum have good diagrams of the vac system on this model MB and plenty of directions and information on how to tune the vac to produce the best transmission performance.
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  #15  
Old 06-06-2016, 10:26 AM
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Clemson - are you saying this is different from my 1981? I thought they were all the same. If they changed and made it backwards in 1984, that is news to me. I have a 1981 300SD and mine functions the way I described it; the upshift is designed to happen with no vac and it bleeds off immediately when you go WOT. I cannot fathom why they would have reversed the operation.

Can anyone confirm? Kerry - are you out there; do you know?

Thx.
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