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Old 07-29-1999, 10:47 PM
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Join Date: Jul 1999
Posts: 239
Hello, owners of jerky transmissions.

Previous owner of my 81 300SD replaced the tranny with a rebuilt (or maybe used) unit at a "garage", not an independent MB shop. (One example of their work is epoxying a tear in the fuel tank instead of replacing it - the patch job developed a slow leak and diesel mess in the trunk. I replaced the tank and decontaminated the trunk.)
The transmission had a severe clunking (or jerky shift) from 1 to 2, bad enough to be concerned for the differential which was taking a pounding if the throttle wasn't modulated during shifting.
Also, there is a flare from 2 to 3, with the RPMs rising about 500-1000 rpms during the shift.
The local MB dealer shop took care of the horrible 1 to 2 shift, but not completely.
The MB dealer shop printout says....
"Checked and adjusted the transmission pressure", and charged $48 for one hour labor.
No parts involved.
I still have to let up on the throttle to avoid the jerkiness.
And finally to the question -
Is it possible the "garage" just swapped the tranny and did not complete the job ? What kind of stuff can I look for that they may not have completed such as final adjustments and settings ?
I suspect "bubba" workmanship and would like to eliminate some suspicions before moving on to other possible causes of this shifting problem, especially before it ruins the differential.
Also would like to be aware of potential catastrophic failures due to inexperienced and negligent shops tacking MB transmission replacements.

Besides this very annoying problem, all I have to do is change the coolant, replace three rubber air filter housing cushions, and keep an eye on the exhaust hanger donuts and this car is ready for another 100,000 miles. (Actually, I am also pricing a rebuilt cruise control amp and diagnostic plug from the Parts Shop.)

81 300SD 190,000 miles.
Old 07-30-1999, 09:55 AM
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Join Date: Jul 1999
Posts: 239
Thanks - was hoping there would be some minimal tweaking that could be performed...

The tank was replaced at the dealer shop, but is not a difficult job if you don't mind breathing diesel fumes.
On the 1981, the vertical trunk liner under the rear shelf has to be removed, and then a protective sheetmetal wall covers the fuel tank. Several screws, along top and bottom, hold the protective sheetmetal wall in place. I had to remove the liners for the side wells first - makes it easier to remove the vertical liner.
(The these three liners are formed rigid and are sturdier then the cardboard jobs you see in cheaper cars but a headache to clean soaked diesel fuel since you can't blast through the fabric.)
The filler neck seems to be part of the tank and positions in the filler door opening. A rubber piece surrounds the neck - I guess to keep it from knocking around on rough rides.
Not sure about procedure on fuel line and sending unit. I guess the first thing to do is disconnect the battery before any work is done to the fuel tank.

Good luck.
Old 07-30-1999, 09:58 AM
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Join Date: Jul 1999
Posts: 239
Forgot to mention an intersting item...

The 300SD fuel tank, at least in my 126/1981, stands up vertically and behind the rear seat back. Only time I've seen a fuel tank arrangement like this.
Old 07-30-1999, 12:53 PM
Posts: n/a
It's placed the same way on 4-door 123 bodies. Not sure about coupes and I'm sure wagons use a different setup, obviously... Nice thing is when you fill up the wieght of the added fuel is between the axles, not just on the rear one...


1982 300D -

Old 07-30-1999, 03:05 PM
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Join Date: Jul 1999
Posts: 239
That must be why I'm able to whip around exit ramps at 70 mph in a beast like a 126 diesel !!
Old 07-30-1999, 03:10 PM
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Join Date: Jul 1999
Posts: 239
re - TXbill's
"It's as if someone has run into you from behind when the tranny shifts."

This is by far the best description I've read of this very common transmission problem.

Anyone out there with any suggestions ?

Old 07-30-1999, 09:56 PM
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Join Date: Mar 1999
Location: Suwanee, GA, USA
Posts: 4,712
There are a few adjustments on the SD that are not on other cars for the trans. There is the bowden cable the modulator valve and there is a valve on the rear of the injection pump that can fail and needs to be adjusted with a special tool. All three have to be right for all of the shifts to feel normal.


Old 07-30-1999, 11:18 PM
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Join Date: Jul 1999
Posts: 239
Thanks, Benzmac !!

Won't hurt to ask, but where is this bowden cable ?

Also, while in limbo with the MB 617.951 engine manual out of print and CD-ROM not ready (plus not Mac compatible), will a Haynes manual be sufficient ?
Old 07-30-1999, 11:22 PM
Posts: n/a
Here is a cheap fix that I hope works for you. Replace EVERY SINGLE rubber vacuum line. Don't just look at the rubber and say "that looks o.k." No, No, No. Replace ALL the rubber vacuum hose in the engine compartment - look carefully to make sure you don't miss any. The look of that hose is decieving. Make sure you get hose that is the proper size that will make an ABSOLUTELY PERFECT seal on whatever it is connected to. Silicone vacuum hose works great - once it heats up it sticks like glue and you'll be assured there are no vacuum leaks. Also, clean out the fitting on the back of the intake manifold that has a vacuum line running off it to the fuel pump. The inside of that little screw gets clogged and can cause these problems too. Good Luck.

Old 07-30-1999, 11:28 PM
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Join Date: Jul 1999
Posts: 239
Thanks, Greg.

I will try that.
Where does one get "silicone" vaccuum lines ?
Also, many of these vaccuum lines look like they are made of some sort of rigid plastic material, not rubber...

Thanks again.
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