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  #1  
Old 07-15-2007, 09:55 PM
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Checking transmission on 82 300SD

I just picked up an 82 300SD turbo automatic. This is my first mercedes so I am not too familiar with their layouts. The previous owner did not have the manuals for it still.
The problem is that the transmission is operating extremely poorly. It will shift from 1st to 2nd gear with no trouble, but it will not shift into any higher gears. It will not shift even if I push it up to 5000+ rpms and keep it there.
I would like to check the transmission oil and the lines, etc., but I'm not sure how to go about doing this on this car (on my Volvo, for instance, there's a dipstick for the transmission fluid, but I did not see one here). Any advice on how to check these things and what other things I should look at?
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  #2  
Old 07-15-2007, 10:11 PM
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What's the shift point (rpm) for the 1-2 shift.........typically........with about 1/2 pedal?
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  #3  
Old 07-15-2007, 10:15 PM
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the shift point seems to be around 2.5k (usually I am hitting about 10 mph) although its hard to say because the tachometer is intermittent (it did come on for a while to show me that I was holding at 5k when I was trying to get it to shift earlier today).
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Old 07-15-2007, 10:21 PM
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Quote:
Originally Posted by Mad2Physicist View Post
the shift point seems to be around 2.5k (usually I am hitting about 10 mph) although its hard to say because the tachometer is intermittent (it did come on for a while to show me that I was holding at 5k when I was trying to get it to shift earlier today).
Well, that's no help........

But, check out the kickdown switch below the accelerator pedal. Disconnect the switch (unplug it) and drive the vehicle again. See what you get.
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  #5  
Old 07-15-2007, 11:20 PM
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I will try that tomorrow in the light. Will this help the shifting directly? Also, while I'm driving it around I'll try to get an accurate reading of the revs when it shifts, although no guarantee as the tach. might decide not to cooperate with me.
In the meantime however, is there an easy way to check the transmission fluid levels/quality? I wasn't able to find a way and neither was my mechanically oriented friend.
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  #6  
Old 07-15-2007, 11:24 PM
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Originally Posted by Mad2Physicist View Post
I will try that tomorrow in the light. Will this help the shifting directly? Also, while I'm driving it around I'll try to get an accurate reading of the revs when it shifts, although no guarantee as the tach. might decide not to cooperate with me.
In the meantime however, is there an easy way to check the transmission fluid levels/quality? I wasn't able to find a way and neither was my mechanically oriented friend.
Either it will help dramatically.........or it won't. There won't be any doubts.

The engine has a dipstick for checking transmission fluid levels. It's under the hood on the right side near the back of the engine. It has a locking cap on the top of the stick. Check the engine in neutral after a good hard run with the oil temperature quite hot.

Quality is impossible to determine unless the fluid is dark brown and/or smells burnt. Neither is a good sign.
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  #7  
Old 07-16-2007, 12:23 AM
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Do your doors all lock when you lock it with the key?

Car came in last week ('83 300D) with a similar trans problem and had also recently begun to need to be shut-off by hand, under the hood, too.
Traced to Vac leak. New customer-his first MB diesel (and a POS in my opinion- but the guy's from Santa Cruz so it probably is a thing of beauty to him. lol)
He was giddy when he found out he didn't need a new trans or a crap load of time and parts.


FJ
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  #8  
Old 07-16-2007, 12:53 AM
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We thought it could quite possibly be a vacuum leak as well. Will have to check that too, but I haven't had a chance to do this yet. I am hoping it is something simpler like Brian suggested.
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1982 300SD turbodiesel
"Rudolf Diesel originally designed the diesel engine to use vegetable oils" so let's all get back to what they're meant to use!
http://www.ybiofuels.org/bio_fuels/history_diesel.html
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  #9  
Old 07-16-2007, 12:58 AM
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On the SD, the locks get thier vacuum from an electric pump in the trunk.

Does the tranny slip?

It's time to get a vacuum pump to check for leaks and other problems.
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  #10  
Old 07-16-2007, 01:17 AM
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The tranny doesn't slip, although the shift from 1st into 2nd is not always what I'd call "smooth." However once in second, I stay firmly in second until such time as I slow way down again.
The locks seem to be working just fine last time I checked.
Where would be a good place to get information on how to do these checks?
One of my problems right now is that the car's location is not the easiest for doing serious work, which is one reason why I'm hoping it is something trivial to fix. However, I fear that it is one of the vacuum lines... will know more tomorrow after I try out disconnecting the kickdown switch and checking the Bowden cable.
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1982 300SD turbodiesel
"Rudolf Diesel originally designed the diesel engine to use vegetable oils" so let's all get back to what they're meant to use!
http://www.ybiofuels.org/bio_fuels/history_diesel.html
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  #11  
Old 07-16-2007, 01:32 AM
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I honestly could not believe the difference some of the suggestions on the forum here made in my 82 300SD. Different tranny problems, but wow - the differences are night and day. Bowden cable, EGR, and vacuum lines.
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  #12  
Old 07-16-2007, 03:57 PM
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A few things:
First thing I did today was to check the Bowden cable. This is the cable that runs from the throttle linkage to the transmission, correct? And on this car it goes into the transmission by the ATF dipstick? If so, then that seems to be working fine. The cable moves with the linkage (about 2 cm) when I move the linkage by hand. So I don't think that is the problem, unless I totally screwed up what I was supposed to be checking.
Next thing I did was to take it for a drive of between 10 and 15 miles. I got the engine racing (5k rpm) since even though there were no highways it wasn't shifting. Then I checked the transmission oil with the car running and in neutral. The level seemed if anything to be high. the color on the white paper towel I uesd to wipe to the dipstick was pinkish (is that bad?). It smelled like celery, but not burning I don't think.
While I had it out, I was able to ascertain that with 1/2 pedal it shifts from 1st to 2nd at around 2k consistently during the short period when the tach. was cooperative.
Finally I looked under the pedal to find the kickdown switch. The only thing I can find is a small roundish thing about the size of a quarter that seems to be quite firmly plugged into something behind the firewall. Is this the kickdown switch? If so, how do I unplug it? This thing is stuck like a mother and I can't get such good leverage down there, so is there a release or do I just have to use brute force?
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1982 300SD turbodiesel
"Rudolf Diesel originally designed the diesel engine to use vegetable oils" so let's all get back to what they're meant to use!
http://www.ybiofuels.org/bio_fuels/history_diesel.html
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  #13  
Old 07-16-2007, 04:35 PM
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Quote:
Originally Posted by Mad2Physicist View Post
Finally I looked under the pedal to find the kickdown switch. The only thing I can find is a small roundish thing about the size of a quarter that seems to be quite firmly plugged into something behind the firewall. Is this the kickdown switch? If so, how do I unplug it? This thing is stuck like a mother and I can't get such good leverage down there, so is there a release or do I just have to use brute force?
That's the switch. And if it is jammed in the down position, that's your problem.

You'll need to find the pigtail lead underneath the vehicle, presumably, to unplug it. Brute force is rarely successful on a M/B.
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  #14  
Old 07-16-2007, 04:54 PM
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Originally Posted by Brian Carlton View Post
That's the switch. And if it is jammed in the down position, that's your problem.

You'll need to find the pigtail lead underneath the vehicle, presumably, to unplug it. Brute force is rarely successful on a M/B.
It certainly appears jammed to me. Doesn't move, no matter what I do to it (I tried to pull it out - no luck. Tried to use some leverage, still no luck. Definitely jammed). In fact when I push the pedal down with my hand, the pedal never even touches the switch even in its furthest down position. I take it that the kickdown switch is supposed to activate when giving a lot of gas, in order to make the transmission downshift for added power temporarily, and now with it stuck the transmission thinks it is always supposed to be downshifted?

Now for me to reveal my ignorance What does a pigtail lead look like?
Also, is this the sort of thing that I will have to jack the car up for, or is will it be near enough to the edge that I can just reach under?
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1982 300SD turbodiesel
"Rudolf Diesel originally designed the diesel engine to use vegetable oils" so let's all get back to what they're meant to use!
http://www.ybiofuels.org/bio_fuels/history_diesel.html
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  #15  
Old 07-16-2007, 04:57 PM
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Originally Posted by Mad2Physicist View Post

Now for me to reveal my ignorance What does a pigtail lead look like?
Also, is this the sort of thing that I will have to jack the car up for, or is will it be near enough to the edge that I can just reach under?
You're looking for two wires and a plug in the general vicinity of the button. I believe you'll find it beneath the floorboard but have not done it on that vehicle.
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