'81 300D modulator?
 

I HATE automatic transmissions, so as a result, I ignore them when they give trouble. This thread will be evidence of that.

I rebuilt the engine in my daughters car about a year ago and ever since it shifts way too early. I checked the line to modulator and all was well. It worked good before that and I can't think of anything other thing that could cause this except the modulator and associated components.

The car is down for some maintenance now, so I want to check the vacuum contraption on top of the valve cover and the modulator.

Any comments or suggestions are appreciated.

Have a great day,

Larry,

Something I found by accident once while doing a valve adjustment was where the bowden cable attaches at the top of the valve cover it can go past the stop and gets to much slack. This made for very early (but smooth) shifts. I thought I had broken a line or pulled something loose. Took some looking before I noticed what was wrong. I have seen another post here where someone removed the black box thing with no bad side effects so I don't know if it has anything to do with the tranny shifts.

aren't you describing textbook Bowden cable too loose?
 

Aren't you describing textbook Bowden cable too loose?

For sure you know way more about these cars than me (just buying my first one six months ago, and not even close to being able to rebuild an engine), but is there some reason that you didn't look at the cable?

As I say, I HATE automatic transmissions. I did indeed R&R the black box contraption during R&R of engine. I now can't wait to get home to give this a quick look. I assumed the problem was vacuum related.

Thanks VERY MUCH for the tips. Rebuilding the engine, no problem. :D Replacing a clutch, no problem.:D Messing with an automatic transmission, ignore it and it will go away.:(

Thanks again and have a great holiday,

Larry,
I have the same issue on my 300D. It is in high by the time I get to 40 no matter what. I have replaced the bowden cable, a couple under hood components and tested the modulator on the side of the tranny. Nothing works. I am going to eventually test the TD (shifts great) and see what the differences are in the vacuum signal to the modulator.

Well, I finally got to this and the '81 doesn't have the Bowden cable you speak of. There is only the vacuum switch contraption on top of the valve cover. Does anyone have any information regarding the vacuum profile from this thing?

If I knew what the vacuum at various throttle positions is supposed to be, I could put on a vacuum gauge and do some testing.

I feel that on this model, the problem is this contraption, a leak along the way or the modulator.

Thanks for any help you can offer.

Have a great day,

Larry:

The following describes my journey and the data I've collected since trying to solve my "flaring" problem between 2-3. Much of it is the same for tranmission adjustment.

The most comprehensive discussion on this is from Steve Brotherton (some kind of tech) who seems to know these trannys inside and out. Perhaps as much as 6 factors need to be in balance for the trannys to shift properly. I have made great improvement even though its not perfect yet.

His information (5 page printout) is available at:

www.continentalimports.com

click on "articles" and then "mercedes-benz transmissions".

He has pics and the whole shootin' match.

Don

engatwork:

did i see you with a gold (looked orange) non-turbo for sale on e-bay? looks like a nice car for the price.

don

Larry,

Sorry for not including this in the former post but another very helpful article for me was from:

www.mercedesdismantlers.com

scroll down to the bottom and click on:

Automatic Transmission Technical Information.

Under that you'll find a couple of great options depending on your tranny.

Don

yea Don - that's me. I am selling it for a friend. The only thing it needs is rebuilt 1/2 shafts - they are noisy. Reserve is only $1200.

Jim:

I was trying to get a friend to buy it today so we could take a road trip. I figured he is at two and I'm at four, so its his turn. He wants to but his daughter is only 2 yrs old and he thinks its a year or two premature.....sigh

Don

my 81 300D
 

Larry...My 81 300D (180K) as of tonight, actually!...does the exact opposite...it tends to rpm up pretty high and shift late...I'm not a transmission person either!..so I don't know?!? Almost feels as though it's "slipping"...however..here's the scary part...the fluid level looks good...and it shifts much smoother when warmed up. Which here in the middle of 100 deg. every day weather Kansas..that doesn't take long! What's going on with this???..any ideas?..I really like this car, and don't mind spending $ on it..(it's a 2nd car)...and...to anyone else out there...I'm looking at a '87 300sdl in Kansas city this wknd..any suggestions?

thanks
sean

Diesel Don,

Thanks very much, this is helpful information. I printed the Steves article yesterday and digested it. Then I just read the wrecking yard article and it really started my thinker to thinking.

Thanks a bunch for sharing your research.


Sean,

In your case, it sounds very much like you have a lack of vacuum, the opposite of my case in which I think I have too much. The system basically "bleeds" the vacuum to lower it. This is how the contraption simulates the vacuum of a gas engine. Do you have any other vacuum related problems such as door locks or slow to shut off? If so, start looking for a vacuum leak.

Good luck,

Sean; re: 300SDL

The 300SDL's engine and tranny are especially durable, compared to the trannies of earlier years. Make sure the shifts are firm and crisp. Pop the hood and look at the belt tensioner. It should not be loose, making a racket or the pulley angled. Make sure the sunroof works (big $$$). If you near some lifter noise, don't worry about it, its a characteristic of these engines. Make sure it starts easliy with minimal smoke. Make sure there is not alof of smoke at full throttle. Good luck and let us know how you make out.

John

Automatics-Ugge
 

You know you guys could save yourselves years of adjusting automatic transmissions by just junking the damn things and converting all your cars to manual transmissions out of 240D or if you're really lucky a 5 speed out of a European 280CE.

Besides not having to constantly have to monkey with the damn things you'd also not have to make reservations and get a printed invitation to cross an intersection.

We're putting together all the components to do our fourth auto to manual on a 300Turbo diesel that we've also converted to probably the first intercooled 300DT in the US and maybe the world. The local MB club President gave my son a manual tranny that he'd run in his 280CE. These manual trannys are cheaper than dirt and so much fun.

Join the care free world, switch!!!

Ben

Ridge,

Are you saying that the manual from the gas engines will bolt to the diesels? If so, this is great news, it opens up the possibility for more gearset combinations, as well as just more availability for manuals.

I have a 240D manual transmission in my parts car that I have considered putting into this 300D, but at this point I am probably just getting the car ready to sell.

Thanks for the note,

Manual transmissions
 

Larry,

That's exactly what I'm saying. The manual transmissions from a gas car of the same series (123) will fit the diesel cars. Better yet the local MB Club President had a 240D tranny in his 280CE while the 280CE transmission was being rebuilt and he found it entirely too high geared. When he got his 280CE tranny back and installed, the gearing was just right.

So the conclusion is that the two trannys while looking the same have different ratios.

Personally, both my son (300DT) and I (240D/300 G-wagen) perfer the 3.07 rear end ratios with the 240D trannys as it gives you the ability to wind the cars up to almost 80MPH in third entering freeways.

Hopefully, this weekend we'll get around to posting pictures of our newly intercooled 300DT. Once we get it converted to a manual tranny, we can really have some fun. Watch for Pixs!!

We're at work collecting all the parts to intercool another 300DT.
By raiding junkyards it looks like one could do it, if they had a manual to guide them, for around $400.00. And it looks great too!

Ben


Ben

Hi,
Just curious.....does your family appreciate you? My ex wife didn't until she had to take her car in for service....first time in twelve years.....hmmmmm....I enjoyed every minute of the story....
Nathan

diesel don,

Thanks very much for the links. The information was invaluable.

I'm quite sure I've found my problem, now I have to improvise a way to fix it.

During the overhaul, I broke the nipple on the vacuum hose that feeds the vacuum contraption. I paid good money for an entire replacement line. As warned about in one of the articles, my new line has no orifice in the supply line for the contraption. This provides too much vacuum to be bled off by thecontraption.

Now I need to improvise a way to put an orifice in the line. I think I can simply push a tiny piece of hose into the nipple with a 1/16" hole.

The hardest part of fixing things is almost always the diagnosis. Now that is done, I just have to provide the fix.

Thanks again for taking time to help,

Larry, like you I always stayed away from that device bolted to the rear of the engine, I considered auto tranny's to be akin to garbage disposals or salt water outdrives .But since I have most everything done except paint on my 126's I have been playing with Bowden cable and modulator Iv'e got my SD shifting much later and smoother working now on my SE.I just printed out Steve's article on MB transmissions what a credit and gentleman he is. I have learned a great deal about these fine cars from both of you.......
William Rogers........

74 240 D "Pearl"
81 SD (Goldie)
86 Euro 500SE with Euro 420 engine"The General"
81 2wd K5 Blazer 454 I built from many
cast off vehicles....."Beaitrice"

William,

I'm completely flattered to be considered even being inside the same ball park as Steve. Good luck with the mixers.

Have a great day,

Larry:

I too was amazed at Steve's article and glad you found it helpful. I even emailed him once and got a quick reply but that was on an unrelated mechanical issue. Since you've helped me about 721 times, I'm hopeful that your tranny will come around.

I continue to be amazed by this forum. I'm now 16 months without taking a car to a shop (one exception was a front end alignment). That translates to cold cash in the pocket.

Don

Larry - did you ever find out what caused the "early shift" issue in the 300D?

Jim,

I gave up on it temporarily. I managed to get the vacuum down a little with a restriction at the supply from the brake booster hose. If I can get some time to get back into it, I believe I will investigate the gadget mouned to the IP.

I also need to give the engine a good going over, it is smoking like crazy. I plan on checking injection timing and maybe putting some injectors on it.

I haven't had time for much of anything except just keeping our drivers going and maintained. I'm also probably about ready for the funny farm. My boss "resigned" last Monday and an Interim CEO was brought in as his replacement. The company is in really serious condition. I don't know just how much longer it will last. I'm sure there will be some "changes" coming in a week or two.

Under these conditions coupled with the really rotten weather we've been having, I haven't really gotten excited about doing anything except working and keeping up with things around the place.

If you have any other suggestions, they will be appreciated.

Have a great day,

Larry,

I disconnected my vacuum feed to the transmission and inserted a vacuum section with a drilled leak in it. In this way, I'm bleeding more vacuum off and have eliminated my flaring condition between 3-4 shift.

I don't know if this would relate to an early shift, but there are some pretty creative things to try.

I did find the bowden cable to affect the timing of my shifts.

Don

Larry, is it too personal to ask what you do for a living ? your travels sound interesting. By the way the Yoko'S on my SE are all that I could ask for, tis hard to get enough of that Euro V 8 even for an old Codgier...........
William Rogers......

From what I understand the device at the back of the IP is supposed to create a "curve" that stays relatively flat until right at the end where it is supposed to have a pretty sharp drop off in vacuum. I may try getting mine to do this after I finish getting it going today and see what happens.

Sorry about the isses with the company you work for.

Jim:

My vacuum bleed valve (white deal atop the back of the IP), would register around 12 inches at idle and fall off to 2.5" at full acceleration.

I therefore suspected it of supplying too much vacuum upon light acceleration. For my car ('83) would flaring when lightly accelerating.

I swapped the vacuum bleed valve with the one on the '84 and had the identical results. Bummer.

Finally just disconnected the vacuum going to the modulator and have a pretty nice ride.

Don

William,

I work for a software company that provides a product used in Industrial Automation. I have been in this industry since 1988 working directly for a software development company. We are known in the industry as a "software house." Our product is used to create Man Machine Inteface systems for control, monitoring and data acquisition.

There was a time when there was much demand for these products and there were very few companies that provided them. There are now MANY companies in the business, and not enough business to go around.

I began by doing engineering services, applying the products, training, support, etc. I then was moved into the sales area due to the fact that it takes technical understanding of such products to sell them. I spent about ten years selling to major accounts and setting up distributors and other partners. I then spent time in marketing, doing various presentations and demonstrations of the products as well as writing various documents and daily tips that were sent out to our technical community worldwide. This is the capacity in which I did the European travel. In July, I was drafted to develop our sales channel by finding, qualifying and signing new distributors and other partners.

The industry has come and gone sort of like VCR's. They are still being made although you can now get them for $40. The state of the general economy hasn't helped our situation, but we are much more directly effected by the manufacturing sector, which has struggled since about mid 2000. Such a massive amount of money was expended for the Y2K scare by the companies that comprise our market, that it will be awhile before their budgets for such products and services recover.

I'm sure I will be able to find another career, but at 53, it's difficult to break into a new industry in the technology world. I'll probably find myself "bustin' nuts" at the Ford house.

Thanks for your interest,