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  #1  
Old 12-09-2001, 08:54 PM
Phill
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300D transmission prob.

Been reading some previous posts on transmission problems. Most of you seem to point toward vacuum as culprit.

My automatic 300D recently started having problems shifting gears also. goes ok into 2nd gear, but somewhat hard. 3rd gear no longer shifts until the RPM are WAY up above normal (at least where it used to shift) and then it shifts hard. Doesn't necessary "clunk" hard, but kind of jerks in.

Now it will NOT shift in to last (4th) gear at all. I have to let completely off the accelerator so that rpm drops for it will shift in. I've check all the visible vaccuum lines up top. Everything seems to be in order. Turns off ok. Any ideas? look underneath?

ps-had a rebuilt transmission installed just 25,000 miles ago.

Thanks!

81 300d 260,000 miles

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  #2  
Old 12-09-2001, 09:35 PM
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Location: Evansville, Indiana
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Sounds like a combination of vacuum leaks, possible misadjusted modulator, and bowden cable out of adjustment.

Check the vacuum line for the transmission system at the main line -- there is a restriction there that can get plugged. It is a small plastic insert, white, I think, maybe yellow. If it is full of crud you will have no vaccuum to the modulator and will get late shifts.

The vaccuum line can be off at the modulator, too, same deal.

Check all the lines for the condition of the rubber connectors -- they get either rock hard or soft and sticky, and leak in either condition. Replace any that look or feel iffy -- you can use similar size vaccuum line from the auto parts store. Make sure to keep any hard plastic bits in the original location -- they are filters or restrictions.

If this doesnt' fix it, and you do have vaccuum to the modulator, it is either stuck or out of adjustment.

Peter
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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
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  #3  
Old 12-10-2001, 11:38 AM
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Join Date: Oct 2001
Location: Ottawa, Canada
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Phill,
I had a problem with hard and late shifts and not going into 4th. It turned out to be the bowden cable which had rusted and partially seized. Lubrication of the cable fixed the problem. Good luck.
Schooner
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  #4  
Old 12-10-2001, 05:56 PM
LarryBible
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Okay, I want to confess my ignorance of the bowden cable and get educated.

After pulling and replacing my daughter's '81, 300D engine the trans has not worked the same. I for the life of me don't know where this cable is or what it does. I don't remember seeing it or disconnecting it.

Can someone educate me? I will appreciate it very much.

Thanks in advance,
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Old 12-10-2001, 07:44 PM
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Not real sure about the Bowden cable on the '81 model Larry but on the '85 it comes up from in front of the fire wall on the passenger side at the rear of the engine and ties into the throttle linkage on top of the cam cover. As you mash the throttle it pulls on the Bowden cable. It is set by adjusting the cable until it lines up with the connector to which it attaches - no tension nor slack in the cable. It should be the only "cable" (when I say "cable" I mean something like a speedo cable or hood release cable - not electrical cable) in this area. It will have one of those "cup" type connectors that you see on the throttle linkage that snaps over the "ball" pivot points. On the '85 model the other end is at the passenger side of the tranny.
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Old 12-10-2001, 08:59 PM
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engatwork

I too need some education on the cable. I have a 80 240D without the cable, and I understand that system, but my "new" 83 300D has the cable you speak of.

Can you explain more about your statement

"It is set by adjusting the cable until it lines up with the connector to which it attaches - no tension nor slack in the cable."

My cable seems to move back and forth very easily, as if it might not be connected to anything. It seems like adjusting the slack would be difficult.

Do you have any idea how this cable interacts with the vacuum signal that is being fed to the modulator on the transmission? On my 300D, at idle I get 20 mm of HG, just off idle it drops to 15, and then it varies pretty much linearly with the throttle position to 4 mm at full throttle.

My 1980 240D has 20 mm at idle, drops to 11 just off idle, and varies linearly to zero with throttle position.

I love the way my 240 transmissions performs, but the 300 seems reluctent to downshift unless I active the kickdown switch. Maybe the cable is too loose.

Any input or direction is greatly appreciated.

Joe
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  #7  
Old 12-10-2001, 09:32 PM
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Location: Evansville, Indiana
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There should be a plastic screw fitting on the end of the cable that screws into a bracket of some sort -- there is on my 87, but this is a different system. Mine is all the way out, and goes back in when the throttle is opened!

If there isn't plastic fitting, there will be a threaded section on the cover of the cable and nut that locks the setting (or a pair, one on each side of the bracket).

The cable should be adjusted by turning the nut(s) until the cable end is touching the throttle linkage but not under significant tension -- that is, not pulled out of the housing and not loose.

Upshift/downshift control is a combination of the vaccuum and cable position. I've also heard that the cable controls upshift point and the vacuum systems is just for hardness/softness of shift, but I cannot verify this. I suspect he former.

More pull on the cable will give later shift, less earlier.

I don't know which models have the cable and which don't -- for sure the W115s have no vaccuum modulator (and no cable, either -- a bellcrank and lever instead!). I know the 722 transmissions have a vaccuum modulator and cable, but I'm not sure if there is another version in between on the W123.

Peter
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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!
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  #8  
Old 12-11-2001, 06:01 AM
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"It is set by adjusting the cable until it lines up with the connector to which it attaches - no tension nor slack in the cable." I mean that the "cup" and "ball" are lined up to be connected and there is no slack in the cable at this point.
My 300D is in high gear by the time I get to 30 mph - it is almost like a CVT transmission. Anyway, I tightened the heck out of my cable one time just to see what the difference was and it still shifted early but shifted a lot harder. I am replacing the vacuum modulator (as soon as I get it from partsshop.com ) just to see if that makes any difference. I can live with the way it shifts because of the way I use the car - 18 mile commute - 3 redlights. In addition, I figure it adds life to the engine/drivetrain to shift early this way. RPMs never get much over about 3000.

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