Tranny adjustment

[derherr65]

I'd like to know more about how the automatic trasnmission is controlled in an '82 300CD.
From my search the transmission has two basic driver controls, the bowden(throttle) cable and the vacuum modulator. Are there any others?
What exactly does tightening or loosening the bowden cable do?
What does turning in or turning out the vacuum modulator 't' do?

[Brian Carlton]

Originally Posted by derherr65

What exactly does tightening or loosening the bowden cable do?
What does turning in or turning out the vacuum modulator 't' do?

The Bowden cable increases throttle pressure inside the transmission and thereby causes the shifts to occur at higher rpm's. The tighter the cable, the greater the rpm required for the shift.

The vacuum modulator increases the modulator pressure inside the transmission and thereby increases the speed of the shift. The more pressure, the faster and firmer the shift occurs. This adjustment can also be done with the vacuum control valve to increase or reduce the supply vacuum to the modulator.

[derherr65]

Excellent, just the type of anwer I was hoping for, thanks.

One other question, if all shifts are fine except the 1-2 shift which is harsh, what does that mean?

[Brian Carlton]

Originally Posted by derherr65

Excellent, just the type of anwer I was hoping for, thanks.

One other question, if all shifts are fine except the 1-2 shift which is harsh, what does that mean?

It means........join the club.........

Actually, most of the older vehicles had a "firm" 1-2 until M/B changed the shift characteristics in the later vehicles. My SD is nowhere near as harsh as my older W123 (1983). I'm not sure if it can be retrofitted economically.

You could try increasing vacuum to the modulator, but, you run the risk of a mushy 2-3.

[derherr65]

Ah, ok. I wondered if that wasn't the case from some things I'd read.

[johntksr]

I had the same symptom with my 82 300sd until recently. I would check the following items as they are typical of the harsh 1-2:

1) check the plastic vacuum levers under the black box on the valve cover. They wear out and are cheap to replace.

2) disconnect the vacuum from the EGR valve - will improve performance as well. This simple disconnect improved my transmission shifts to like new condition.

3) adjust Bowden and Modulator valve if necessary.

[PanzerSD]

So how come I had to ask the same damn question three times before I got any response??....anyway...I have to say Brian, that your first responce was probably the most concise, the least confusing description of the function of our transmissions, that I have ever been able to find anywhere...Thank you..

[Brian Carlton]

Originally Posted by PanzerSD

So how come I had to ask the same damn question three times before I got any response??....

You're from Canada........nobody answers questions from Canadians........

[PanzerSD]

Touche!

[derherr65]

Originally Posted by Brian Carlton

You're from Canada........nobody answers questions from Canadians........

Oh I hate you. I'm just at the tail end of a nasty flu, ribs hurt, throat like raw meat, and you make me laugh.