Hi there- Some of you probably recognize me from another MB forum, although I come here often to look for info, but I'm not sure I've ever posted before. There seems to be some very knowledgeable people on here, and I'm hoping someone can help me out.

I picked up a 1981 300D in NYC on Saturday from a BW forum member, and drove it the nearly 500 miles home without too many troubles. I did have some trouble, it blew a coolant hose that I had to change. No big deal.. easy fix.

There is something screwed up with the transmission, however. It slips, or flares, or whatever. I'm still not entirely clear on the two terms, and how they differ.

When it gets to the point where it wants to shift, it'll start to try and change gears. Then it'll just kind of rev up, and if you let off the pedal, it'll drop into the next gear. This transmission has first gear start. I'm not sure whether or not that's a modification that was done to it, or if 1st gear start was original to this transmission.

The 1-2 shift is fairly fast, and maybe even slightly harsh. I'm not horribly concerned with that one. The 2-3 shift is extremely sloppy. You have to let off the pedal for it to drop into 3rd. The 3-4 shift is by far the worst, and you have to entirely release the pedal to the point where the car starts slowing down in order to get 4th. I've found that if I put the selector in "S" and drive up to 3rd gear, push it to 55 or so, I can then let off the pedal and shift into D and then resume accelerating when it finally drops into 4th.

I've searched myself to death for the last few nights, on many forums, and there is so much information, but I just can't nail exactly what to do.

There is no Bowden cable at all on this car for the transmission- so I'm guessing it's entirely vacuum controlled- and according to what I've read that is correct for 1981.

The vacuum lines were sort of screwed up. I've found several different diagrams on here and online elsewhere, and also the EGR vacuum diagrams on my manual CD's.

I've read this:
It's CRITICAL... how you set your transmission's vacuum system on your diesel MBZ... - ShopForum
and this:
Mercedes-Benz Transmission, Steve Brotherton, ImportCar, February 2002

and about 50 other posts on various forums.

I'm trying to basically figure out, do I have a bad transmission here, or is it just a vacuum mess?

On the vacuum diagram, basically this one:
http://home.comcast.net/~phantoms/va...gr_82_300d.jpg

I'm confused about something. See the little letter "a" It says vent to passenger compartment. What the heck is this? Just a dead end somewhere? I can't actually find it on the car. It's supposed to be a black line. For that matter, on every diagram I've looked at, there is supposed to be a black with a white tracer to the transmission, and the one going down there is just plain black... so hmm

I've gotten it down to the point where the line I think goes to the tranny has more vacuum at idle than when you bascially flor it- and that's supposed to be right. I don't have exact numbers, as my co-worker has my vac guage. I'm going to have to get that back tomorrow and get the vacuum control valve adjusted perfectly, 10" at idle, and near 0" at WOT.

To answer some usual questions that might come up, the fluid level is good, and the transmission was serviced a few thousand miles ago.

Any suggestions would be awesome, I'm getting mighty frustrated with this thing. It's a pretty nice car, but it's not useful as a daily driver until I get this sorted out. It sucks, because it runs very well, and the chassis is tight as a drum. It needs some cosmetic attention, and a little body work, but if I can get this fixed up, I think it'll be a reliable car. I'm starting to think it would be easier to get the manual 4 speed at the JY and fight with that conversion than get this stupid thing working right...

Aaron-

any ideas?

You need a K1 spring upgrade kit. That should help the 2-3 flare enough that you can soften the 1-2 shift to a tolerable level. Many of us have spent plenty of time tuning and tinkering with the various adjustments on our old worn transmissions to return them to tolerable operations.

__________________
'79 300D, Ivory "Gunther" ......going
'81 300SD, Metallic Blue Silver, The Grey Ghost.....going
'87 300D Turbo ...gone
'05 CDI.... gone

^^^ K1 could be it.

Adjusting the modulator could help also.
http://www.mercedesdismantlers.com//722.118_transmission_adjustments.html

Or B2 piston is the culprit.
http://www.peachparts.com/shopforum/showthread.php?t=131124

__________________
1983 123.133 California
- GreaseCar Veg System

^^ Or perhaps all of that ^^.... and then some...

I've done some digging of my own, and I got my vacuum guage back from my coworker today.

The vacuum to the transmission at idle is around 20", and it only goes down to about 14 or 15" at full pedal travel.

That should be most of the problem, as everything I read states that there should be around 10-12" of vacuum at idle, and it should drop to nothing at full pedal.

I think the vacuum control valve mounted on the IP is garbage, I took the cap off for the adjustment and some genius "mechanic" had gotten at it with a pair of vice grips....

I removed it from the IP and I could not get it to adjust no matter how hard I tried.

Following the vacuum lines... I don't get what the heck the engineers were thinking when they designed this system at all.

I still have very limited knowledge of how the transmission is supposed to be controlled by the vacuum in the first place. Maybe somebody could shed some light on how the modulator is supposed to work, and if I know that, I should be able to make this work properly once I get the parts that I need.

If I remove the vacuum line to the transmission, it does not shift at all. I took it down the road.

Hooking it back up makes it all crazy with the flaring and it requires removing my foot from the pedal all the way to get it to shift.

So how do different amounts of vacuum control the shift points and firmness?

If no vacuum means no shift, and too much vacuum means horrible shift... what happens in between, like during normal driving at half pedal?

Do I assume that at full throttle and no vacuum, the shifts will hold out as long as possible? Thats how it's supposed to work- but then wouldnt the transmission eventually shift with the line disconnected?

I think I've figured out that the less you get into it, the softer the shifts will be, and the harder you press down the pedal, the later, and firmer they will be.. is that right?