I bought a 83 300CD a couple of months ago. I've had other 123 diesels but this is the first turbo. I didn't like driving this one in town because it was a beast. Slow off the line and then crazy boost coupled with hard shift 1-2, and sloppy slip shifts on 2-3 and 3-4.
Yesterday I adjusted the modulator 3/4 turn clockwise and shifts are firm but not jolting, except 1-2 is a bit hard if accelerating hard, that's okay.
Bowden adjusted to make it shift when it should dependent on acceleration rate.
Now all was good with the tranny shifting but the car was still slow off the line and then turbo blast off a bit over 2000rpm. Not so nice to drive around town. So, today I removed the anti-tamper device on the alda and ended up at 3/4 turns counter clockwise by adjusting and test driving.
Now I don't have to press down as much on the accelerator and it pulls strong right off the line. Turbo boost is barely noticeable unless I'm really accelerating hard, the power is strong but very linear now.
The only thing I noticed is that the shifts are not as firm again. I believe this is because I don't have to press the accelerator down as far to get great acceleration so, the vacuum device at the IP hasn't lowered the vacuum to the modulator as much as when the accelerator had to pressed down farther prior to the alda adustment. I'm sure that 1 or 2 clicks clockwise at the modular adjustment will firm the shifts back to where they should be.
This car is now fast right off the line and all the way to highway speed, very linear acceleration and no longer a beast around town. I burn bio-diesel so now I have power, economy and the car is more environmentally friendly than my 4 cylinder 4 runner. I learned all that I needed to know from all the members on this forum and from visiting one of the members that lives about 2 miles away (Fisherman). Thank you all, guess I can sell the 240D now that I'm happy with the 300CD.

Don't adjust the transmission vacuum modulator, it's probably high enough and you don't want overpressure!

Adjust the vacuum valve at the IP so the vacuum drops faster with less pedal travel.

Best Regards,
Jim

You are near Fisherman...where are you at?
Another Northwesterner...?

You may be right about adjusting at IP rather than modulator. I'm not familiar with how to make that adjustment. I know which device it is but haven't made any adjustments there. I'd like more input first though. This device at the IP drops vacuum from max. vacuum toward atmospheric (less vacuum) as you press farther on the accelerator. I thought the vacuum modulator bled off more of this vacuum as you turn it's adjustment clockwise to provide a firmer shift, so, how would that cause an overpressure situation? I'm just asking because I don't understand. I do understand your reasoning because since I now press less on the accelerator, I need to send a lower vac. signal to the modulator from the IP with less depression of the accelorator.
1. Can you tell me how to adjust the device at the IP that sends the vacuum to the tranny vacuum modulator?
2. What is that device called?
3. What would be getting over-pressurized if I make too much of an adjustment at the tranny modulator?
Thanks for any help on this.

need....pictures....

__________________


1980 500SE/AMG Euro
1981 500SEL Euro
1982 380SEL
1983 300TD
1983 500SEC/AMG Euro
1984 500SEC
1984 300TD Euro
1986 190E 2.3-16
1986 190E 2.3
1987 300D
1997 C36 AMG
2003 C320T 4matic

past: 1969 280SE 4.5 | 1978 240D | 1978 300D | 1981 300SD | 1981 300SD | 1982 300CD | 1983 300CD | 1983 300SD | 1983 380SEC | 1984 300D | 1984 300D | 1984 300TD | 1984 500SEL | 1984 300SD | 1985 300D | 1986 300E | 1986 560SEL | 1986 560SEL/Carat | 1987 560SEC | 1991 300D 2.5 | 2006 R350

Hey Brandon, I'm in Bend and lucked out finding that Fisherman is on the forum and lives close to me. I went to his house the other day and learned a bit more about the vacuum system and what was going on with my sloppy tranny shifts. Was able to cure the problem which was a relief, I was already getting estimates on a tranny rebuild just in case.
I saw your posts and pictures when a few of you met near Portland a couple of months ago. I'd be interested in another gathering but I don't drive the MB when the roads are bad especially across the mountains. Maybe you can plan another gathering later in spring or summer. Maybe make a run to Multnomah Falls or somewhere fun if we could get enough people to make it fun.
Should probably of started another post for this stuff as I'm now off topic but what the heck. Good to chat with another MB fan in the NW.

Today I dremeled off the cap on my alda, and then adjusted it a good 1 and 3/4 counter clockwise turns.....WOW My car hauls like never before, not *that* much smoke either.....barely anything visible in the daylight, especially if I am driving gently. I stopped using mystery oil the last fillup, and report a 5.5mpg increase in mileage.....I had a super high concentration of MMO in there on the previous couple of tanks, and I was down to 18.2mpg average... So by stopping it for two tanks I jumped up to an average of 22.8mpg! I think I was using wayyy too much MMO, that was the problem. From now on I am going to use it only occassionally, and probably just do an occassional purge instead. In a couple weeks I will be changing the oil over from Delvac 1300Super to Shell Rotella T.......ordered the items needed from fastlane last night. Now if only it'd get a little warmer than 14 deg's out

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

I believe that with NO vacuum at the vacuum modulator, the trans pressure will be maximum. It's at this low/no vacuum that the internal pressure can be set too high. As I understand, the pressure is set to a given value, which will produce firm, very firm or extremely firm shifts depending on clutch condition, etc, and the vacuum is used to 'soften' the shifts.

Have a look at this article, considered to be The Source for transmission adjustments.

http://www.continentalimports.com/ser_ic20242.html

Best Regards,
Jim

Thanks for that link Jim. That is the best info. I've read on tuning the transmission vacuum and shifting characteristics. Before changing anything now, I'm going to check my modulator setting as described in the write-up and then tune the vacuum signal curve at the IP. I think I'm tuned pretty close to what is needed but your input on not over-doing the modulator adjustment appears to be right on. Excellent info..