Hello everyone, I just purchased a 1983 Mercedes 300d with 155,000 miles and am trying to resolve a transmission problem. The car is "lagging" when shifting from 2-3 and 3-4. At the same time when the car "lags", and right before shifting, not only does the car slow down a tiny bit but I can also hear the rpms go up and like a small "slipping" noise, then it shifts. This all happens in fractions of a second.

Currently I have just changed the transmission fluid (including from the converter) and the transmission filter. This did not help at all.

I am now looking at the vacuum system. Using a MityVac, the "T" connector that runs of the vacuum pump has 20hg. This seem fine according to what I had read online. Now comes the part that "could" be the problem. I connected the MityVac to the line that goes to the modulator valve. When the car is on idle, It has 15 hg. When the car is fully accelerated, it goes down to 10hg. I read somewhere online that when the car is accelerated that it should fall down to 0? Could this be the problem? If this is the problem, which part do I need to replace

Thanks everyone,

Adiel

ps: I am attaching a picture of where I connected the mightyvac which also shows the black line going to the modulator disconnected.

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Right below where you have the mighty vac tied into the y connection is a off white plastic part. If you look on the side of it toward the drivers side tire you will see what looks like a cap. You can pry that cap off and there is an adjustment underneath there that you can adjust and get the pressure to go to zero. In addition, at the back of the white plastic part you will see where you throttle linkage moves and has a lever that comes up and is supposed to stop near a "stop" pin. There should be approximately 1/16" (don't remember the exact number) clearance between the stop lever and the pin at WOT.

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Jim

on top of your valve cover is a little black box with several vac hoses. Inside there are two little valves with a cam system conected to the fuel delivery linkage and on top of those little valves are little nylon fingers. They wear out and need to be replaced so see if they are worn. If so replace them and your problems should go away.

Simply changing the trans fluid and filter will not dissolve the varnish built up in those tiny holes and sealing balls in them.... which control the hydraulic fluid going to the hydraulic actuating parts of the automatic clutches......so if the flow is restricted then the action is like ' slipping ' a manual clutch... which , if left very long, wears out the friction material on the clutches....
If you look up TRANS-x and look at the posts you might want to give that a try... after you replace the stuff mentioned in the above posts.... cheap and does not keep you from going to the next step if it does not work... but give it a couple of hundred miles ... and be sure to read the can and make sure you know the total fluid capacity of your transmission.... you may need two cans like I did in my 81 wagon trans....You can syphon out the amount you need to remove so you can put the Trans-x in ...

I'll admit to the trans-x use myself, did no harm and I *think* did some good along with a few fluid changes. I'd not leave it in more than 100 miles or so, if that.


A quick check before you spend time and money here is to pull the modulator line completly, as in no vacuum. If it shifts like a rock at all times then, no slip, no flair, there is hope. If it does not, one could jack up the line preasure a little via the adjusting T handle on the modulator at the trans.

There suposed to shift pretty hard, but it's all subjectivce as heck, and they all wear differently. You should definantly have 0 vacuum at full throttle however. There is a spec in the FSM where you position the lever on that bleed valve on the injection pump at a certain position and adjust it to have a given vacuum at that setting. "Theoreticaly" then it should be right.

There are also colored "orifices" used to skew that vacuum curve up and down from a given throttle position, I'm still persuing information on them. My curve is good, my 1/4 throttle on up shifts are fine, but my very light throttle 3/4 is still soft, as in there is too much vacuum at that throttle position. It's an ongoing adventure.

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One more Radar Lover gone...
1982 VW Caddy diesel 406K 1.9L AAZ
1994 E320 195K

I think my modulator is either disconnected or gummed up because it shifts really firm all the time, regardless of pedal position. It is annoying at less than 1/4 throttle, but above that it's okay... quick and crisp. I'm still deciding whether or not I should do anything about it.

I like em a little hard to be honest, I've driven so many old domestics with big motors and shift kits, just isnt that anoying.

What WAS anoying, was the clunk on downshift when you have no vacuum, that was driving me nuts. You can hardly feel it at all downshifting now, thankfully. And you better watch yourself accelerating in the rain, it will toss the rear a few feet sideways when it goes 1/2 and sometimes 2/3.. That's kind of anoying from a safety standpoint, hard to get out of someone's way when you have to stay off the throttle.

I keep telling myself it's a wonderfull thing, but I really don't like this transmission much at all.

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One more Radar Lover gone...
1982 VW Caddy diesel 406K 1.9L AAZ
1994 E320 195K

I love my transmission. My SDL's 1-2 shift is seamlessly smooth all the time; it's usually the 2-3 shift that clunks at less than 1/4 throttle. Downshifts aren't neck-snapping like my 190 was when it was leaking vacuum, so maybe this is just the way my modulator is adjusted. I'll tinker with it one of these days when the weather warms up.

That's my problem, I don't know how there *suposed* to shift. I do know mercedes made running changes to them in several parts, like the valve body, thoughout it's life.

If I can ditch the part throttle 3-4 slip and make it hold 2nd a little longer at light throttle I think I can live with it. Part throttle downshifts would be nice, but hey..

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One more Radar Lover gone...
1982 VW Caddy diesel 406K 1.9L AAZ
1994 E320 195K

Hello, thanks for everyone's help. I did not get to work on the transmission to much today but here is a summary of what I did today:

1. On the regulating valve, set the clearance between the flat
on the lever and the stop pin to 0.5 mm

2. Tested Modulator valve and it holds vacuum for five minutes with no leaks.

3. Set a distance of 10mm between the stop pin and the lever on the regulating valve. With the engine at idle and the distance at 10mm from the stop pin, I set the vacuum reading to 6.0hg using the adjusting nut on the regulating valve.

This only made a "small" difference. The slipping continues. Tomorrow I will go to the dealer and purchase three of the plastic valves in the vacuum system and keep everyone up to date.

Thanks again everyone,

Adiel

I suspect your going to end up needing to monkey with the line preasure, adjusting T handle on the modulator.

People say set it with a gauge and nothing else, but that seems unrealistic to me. Adjust it by feel, such that full throttle upshifts are apropriatly bone jarring, the rest of the system for part throttle can be tuned.

Have you adjusted the cable?

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One more Radar Lover gone...
1982 VW Caddy diesel 406K 1.9L AAZ
1994 E320 195K

Do you have a hesitation going from neutral to drive (or reverse)?
I'm wondering if your problem is related to mine.
(slow engagement & soft shifting).

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D

A reverse engagement delay is pretty normal and "indicative of internal wear" for whatever that's worth. I have about three seconds, none foreward, and it will chirp the 1-2 shift under wide open throttle acceleration.

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One more Radar Lover gone...
1982 VW Caddy diesel 406K 1.9L AAZ
1994 E320 195K

Yours sounds like a different problem. I've got about a 3 second delay going to drive or reverse (you can't even feel it engage when it does) and all shifts are soft. I'm going to check the spring in the valve body described below.

http://www.transmissionspecialty.com/parts/parts/68942-01.htm

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D

Ok, I finally got back from the mercedes auto parts. I ended up buying just the Brake Booster Vacuum Line. I got a pretty good price. It is German-Made and it was $28! I have not installed it yet but...now getting back to car, I think I am getting closer to the problem! Wolf_walker posted the following:

I went ahead and did this test since I had not done this. I disconnected the line that goes to the modulator valve and ran the car and guess what? The slipping went away!!! I shifts very "tough" into every gear but NO SLIPPING! So it looks like the problem is definitely in the Vacuum System? Either the modulator valve or something else? What do you guys think?

Thanks again everyone,
Adiel