1981 240D vacuum issues - PeachParts Mercedes-Benz Forum

unknowncross · #1 02-03-2019, 06:57 PM

So I did a quick search and I have been having a hell of a time finding a diagram that matches my car... And that's the main issue I have. I just bought this car on Friday.

I believe someone removed the EGR so I'm not sure how my vacuum system should lock, and i'm also not sure what all the lines go to. The diagrams I find list colors but it appears that many of the lines have been switched with newer lines.

Anyway, my issue is that the car revs really high before it tries to shift, but when it shifts it feels like a normal shift. No grinding noises or stuttering or anything. The fluid is good and up to proper levels (I checked earlier today just to be sure) The previous owner told me that he kind of winged it when it came to the vacuum system, he didn't have a diagram and there's not one on the car I already checked.. The problem is the car he based it off of I believe is a 85 300TD... I'm not sure how much the routing changed but I think enough to cause issues.

Link to album: https://imgur.com/a/hgPeL4v

I'll try drawing a diagram showing how everything is routed tomorrow, looking at the photos I realize that is likely the easiest way to understand how things are routed at the current time.

...

vstech · #2 02-03-2019, 08:30 PM

FYI, please upload pics to our server, because image hosting sites eventually drop them, or lock them up requiring fees... etc.

unknowncross · #3 02-04-2019, 10:20 AM

Thanks for the information vstech! I'll do that in the future.

I found a couple vacuum diagrams that I'm going to try this week (I'm working all week so time is tight) none of them look exactly like mine so I think some things including the egr are removed, which makes it a little difficult.

moon161 · #4 02-04-2019, 10:38 AM

When went and tried to go through it on my old 240D, I found that the EGR valve didn't work (probably for a long time) and the stainless nuts and bolts holding it in had galled into one piece of metal. As long as their an EGR diagram on the sticker on the sheet metal under the hood and near the radiator and the vacuum routing seems to match it for inspection, just ahh. Well, you don't buy one of these because of the low emissions, except for C02 at least. At least check the EGR valve before going through some trouble.

To make sense of it, as I remember my federalized euro 82. It was probably imported in '85, as that's the only way NY would registers it, as an '85.

There was a mess of levers that operated a butterfly over the mouth of the intake manifold that was closed until maybe 80 or 90% throttle when it opened. This was to make manifold vacuum. The smooth operation of this complex mechanism was a testament to centuries of german clockmaking tradition.

There were 3 or 4 vacuum hoses and a push rod that went to a plastic box on the valve cover. One or two went to the thermostat housing, the other to vacuum supply. Another to the EGR valve.
If you opened it up, there was a rubber hose that got pinched off at full throttle.

I think the basic system operation was:
Wide open throttle disables EGR.
The EGR valve opens when the motor is warmed up.
The butterfly creates manifold vacuum so that the manifold sucks in the exhaust gas when the EGR valve opens.

unknowncross · #5 02-07-2019, 10:03 PM

Well I traced some of the lines. The vacuum line to the transmission wasn't hooked up at all. Does anyone know how I can hook the line? I'm not sure about the routing or where it's supposed to hook up exactly. I know there's a vacuum modulator but I'm not sure where on the transmission.

Also thank you for the run down on how the Egr works! It appears my car just simply does not have one however. I don't believe it came factory without one but rather it was modified.

tyl604 · #6 02-08-2019, 09:23 AM

I do not know the 240D but I have a 1981 300SD. The vac modulator on the tranny is round and has a ridge in the center so you can turn it CW or CCW to adjust the shift. A vac line runs from the vac modulator (there is a nipple) to the VCV (vacuum control valve) up front at the injection pump. In the pic below the VCV is the white plastic gizmo with vac lines attached. It is supposed to supply about 10-15 ihg vac to the vac modulator until you hit the accelerator at which time the vac goes quickly to zero so you get a smooth upshift. For downshift it applies vac through the modulator to give a smooth downshift.

For the 240D I am guessing you have the same setup. So run the vac line from the VCV back to the vac modulator. Without you will get really bad upshifts, jarring. But the downshifts should be OK without it.

vwnate1 · #7 02-08-2019, 06:09 PM

Subscribed .

unknowncross · #8 02-08-2019, 08:04 PM

Quote:

Originally Posted by tyl604

I do not know the 240D but I have a 1981 300SD. The vac modulator on the tranny is round and has a ridge in the center so you can turn it CW or CCW to adjust the shift. A vac line runs from the vac modulator (there is a nipple) to the VCV (vacuum control valve) up front at the injection pump. In the pic below the VCV is the white plastic gizmo with vac lines attached. It is supposed to supply about 10-15 ihg vac to the vac modulator until you hit the accelerator at which time the vac goes quickly to zero so you get a smooth upshift. For downshift it applies vac through the modulator to give a smooth downshift.

For the 240D I am guessing you have the same setup. So run the vac line from the VCV back to the vac modulator. Without you will get really bad upshifts, jarring. But the downshifts should be OK without it.

Thank you! I wasn't sure if the vacuum line went to a junction between the VCV and modulator or not. The line was running down to the passenger side. I'm going to see if I can find the modulator and get everything hooked up properly.

Should there be anything else hooked up to the VCV? at the current moment I have a Y junction, one side goes to the transmission the other leads to a four way split that provides vacuum for all my internals. If I understand correctly that is wrong, and instead the internals should be connected directly to the switch over valve but I want to make sure. I do not seem to have a EGR on this engine, I do not know if the engine is older or if perhaps the EGR was just removed.

tyl604 · #9 02-08-2019, 08:53 PM

I do not quite remember now and the diesel is in the garage. Will try to look tomorrow after Habitat. In general the vac goes through the VCV and then to the vac modulator. But it does Y a couple of times before the VCV. Again this is for a 300SD do I am not sure that your vac lines will be exactly like mine.

At this point you will be better off just putting a golf tee in the lines that go the the EGR. I will take a look at mine. That is what I did about two years ago and saw no ill effect.

More tomorrow with luck.

unknowncross · #10 02-08-2019, 09:32 PM

Quote:

Originally Posted by tyl604

I do not quite remember now and the diesel is in the garage. Will try to look tomorrow after Habitat. In general the vac goes through the VCV and then to the vac modulator. But it does Y a couple of times before the VCV. Again this is for a 300SD do I am not sure that your vac lines will be exactly like mine.

At this point you will be better off just putting a golf tee in the lines that go the the EGR. I will take a look at mine. That is what I did about two years ago and saw no ill effect.

-snip-

More tomorrow with luck.

Thank you! For some reason mine has the junctions AFTER the VCV, not before. So I think something is wrong with my system... But more importantly.. I can't seem to locate the transmission modulator. I found where it's SUPPOSED to be but there's... Something there instead. Some weird plug, maybe a electrical plug? Is it possible it's on the passenger side? the transmission is filthy and i'm not sure where the vin for the transmission is, so I can't figure out the exact model.. In the morning i'll have to crawl under again and see if I can scrape off enough gunk to find some sort of numbers...

this is the plug i'm referring to. It's right in front of the shift linkage, where logically the modulator should be...

unknowncross · #11 02-08-2019, 11:04 PM

Thanks for all the tips guys! I plan to have this as my daily driver, although it's no huge deal if it breaks down because my work is less than a 30 minute walk away. My dad was a mechanic back in the day before he got into trucking so he taught me a lot of smart things. Like always put a tire under the frame rail so if a jack stand does fail you won't get crushed. The shaking the car tip is something I always do when I put my cars on stands to make sure it's secure.

Getting rags at a thrift store is actually really helpful, I never thought of that before. I have some old clothes I have that i'll use, and I learned to wear safety glasses (over my regular glasses) the hard way. I ended up with a shard of metal in my eye when a seized bolt sheared its head off, I got it out but it was incredibly painful. Now I always wear safety glasses and gloves when doing anything on a car. Once is enough to remind me to be smart about my safety.

And i'll look around on craigslist for some jack stands, my boss said he has some ramps he can't use that he is willing to give/sell to me, so I may see about that first. Thanks for all the help guys! And don't worry, I will take PLENTY of pictures.

unknowncross · #12 02-10-2019, 02:09 PM

I managed to get the vacuum line hooked up! I didn't have to raise the car, but it was a bit of a contortion exercise.. I had to do it blindly, I couldn't directly see the modulator. For anyone that has the same transmission as me (722.117) the modulator is on the right hand side at the rear of the transmission, behind the two piston covers just before the output shaft.

I'm going to be test driving it soon to see if the issue is fixed or not. I believe I need to reroute many of the vacuum lines since they don't seem to be routed correctly according to any manual or schematic I have seen...

Pictures pending as soon as I can upload them.

vwnate1 · #13 02-10-2019, 03:54 PM

There you go ~

These are actually very basic cars, well engineered and amazingly well built, at close to 40 years old of course there will be some issues, some are worn out things, some are in need of adjustments and as you've discovered, often the list of DPO & DPM bodges is daunting and can appear endless, don't let it throw you, take the time to follow the basics, the EGR isn't critical and won't affect shiftingeso ignore it for now .

Remember to get some new vacuum hose , you're going to need far more of it that you can inagine .

many here like the blue silicone vacuum hose as one size fits every vacuum nipple on the entire car .

i dopn't like the look of it but it works great and lasts forever .

You have to fix all the vacuum leaks before you begin adjusting the shifting .

Find either a Mity-Vac tool of a vacuum gauge, old vacuum gagues were sold as fuel pump testers and are often available @ Auto Jumbles , pawn Shops and Thrift stores for $5 .

The Mity-Vac tool is the esiest to use as it comes with adapters and can be used to find the slow leakas in your central locking and so on....

About $45 for the Mity-Vac tool new .

unknowncross · #14 02-11-2019, 08:32 PM

Quote:

Originally Posted by vwnate1

There you go ~

These are actually very basic cars, well engineered and amazingly well built, at close to 40 years old of course there will be some issues, some are worn out things, some are in need of adjustments and as you've discovered, often the list of DPO & DPM bodges is daunting and can appear endless, don't let it throw you, take the time to follow the basics, the EGR isn't critical and won't affect shiftingeso ignore it for now .

Remember to get some new vacuum hose , you're going to need far more of it that you can inagine .

many here like the blue silicone vacuum hose as one size fits every vacuum nipple on the entire car .

i dopn't like the look of it but it works great and lasts forever .

You have to fix all the vacuum leaks before you begin adjusting the shifting .

Find either a Mity-Vac tool of a vacuum gauge, old vacuum gagues were sold as fuel pump testers and are often available @ Auto Jumbles , pawn Shops and Thrift stores for $5 .

The Mity-Vac tool is the esiest to use as it comes with adapters and can be used to find the slow leakas in your central locking and so on....

About $45 for the Mity-Vac tool new .

I am probably going to order some new vacuum lines and connectors this week, and i'll be ordering some new fuel line as well, mainly for the injector return lines. The injector lines are currently leaking.

I bought a brake bleeder that has a vacuum gauge attached and I've been using that, that's actually how I learned the vacuum line to the transmission was disconnected. It has been working surprisingly well. it doesn't have all the fittings the mity-vac has but it has enough.

I'll be driving the car to work tomorrow, so we'll see how well it does. The drive there is very short so I doubt i'll have any issues on the way but it'll give me a chance to see if I fixed the issue or not.

vwnate1 · #15 02-12-2019, 12:04 PM

Cool beans ! .

Keep us posted please .