Mercedes-Benz 300-Series
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On a 1983 MB 300 SD what could be wrong when the downshift upshift is rough and fluid level is ok?

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2006-08-19 00:11:14

it sounds like a vacum issue, get a manual or have it serviced

n0rt The vacuum issue took me to further findings. Besides

improving the vacuum lines, I also got a tip that worked very well:

Adjusting the Control Pressure Cable. It is located on top of the

valve cover where several other connecting rods are, near the

backside of the valve cover where the Mercedes star is. The control

pressure cable is the one that is packed into an approx. 3" long,

black rubber wrapping. What you do is you pry off the ball socket.

Use suitable tools that aren't too rough on the ball socket and

head. You might need to twist and crank it quite a bit until it

comes apart. Once it's apart, you push the ball socket backwards

(in the direction where the cable goes) and then pull it slowly

forward until you feel a slight resistance at one point. Don't move

it any further. If you miss, repeat as many times as needed until

you got that point. Now adjust the control pressure cable with the

adjusting screw that is located right behind the cable holder until

the ball socket is exactly above the ball head. Attach the ball

socket and the ball head in this position. It might be a good idea

to note down how many turns you had to adjust the cable so that you

could go back to that setting if shifting worsens (in case your

vacuum system is way off and the cable setting maybe was done

intentionally to compensate). This procedure seems to be

appliccable for all MB turbodiesel 1981 to 1984. It improved

shifting on my 1983 MB 300SD tremendously, and it is now

practically all smooth up and down. Before, I expected the tranny

to come apart any time of shifting. I also found an excellent

article "Mercedes-Benz Transmission Vacuum Control system

'Tuning'", by Steve Brotherton at

www.mercedesshop.com/Wikka/TransVacTune.


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