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  #1  
Old 09-17-2002, 10:54 AM
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Join Date: Jul 2001
Location: Olathe, KS
Posts: 40
Transmission flare - '83, 240D

I am trying to track down a shifting problem on my 83, 240D. I have used the search function but come up with some conflicting info. The shifting is very soft going from second to third and third to fourth when under light acceleration. Shifting if firmer under heavy acceleration. I have measured the vacuum at the line going to the transmission module. At idle speed the vacuum gauge reads about 16" - at full throttle it drops to about 5". I have read that it should drop to zero. I have also read that it should drop to about 5".

Questions:

1) Which is correct zero or 5 inches at full throttle?
2) Do I have a bad vacuum control valve (VCV)?
3) Is there any adjustment that can be made to the VCV?
4) Is there a "vacuum bleed" line that could be blocked?

Any help you can give would be appreciated.


Bill
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  #2  
Old 09-17-2002, 12:10 PM
Nate1954
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Hi,

The vacuum on a non turbo engine is the result of the piston action creating a vacuum in the cylinder and air flowing through the intake manifold, the intake valve, to the cavity in the cylinder.

Depending on "where" you take the vacuum measurement and the tubing size or orfice size of your vacuum gauge, your measurements my be "off" a bit.

16" at an idle sounds pretty good.....5" at open throttle sounds ok but it should start climbing as the engine speed increases.

0" at the onset of open throttle is not uncommon but may actually be the result of "lugging" the engine....or....the vacuum connection being near the throttle body or "butteryfly" valve of the intake manifold.

The transmission has spring loaded valve and hydraulic pistons that activate friction bands around planetary assemblies to accomplish gear changes....

Has it always shift this way? Have you had the transmission serviced? Have you had the modulator tested?

Nathan
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  #3  
Old 09-17-2002, 04:54 PM
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Join Date: Jul 2001
Location: Olathe, KS
Posts: 40
Nathan,

I have been working primarily on low vacuum problems - slow/intermittent door lock operation and loonnnnnnggggg engine shutdowns. I just bought the car about 4 months ago. It has always shifted a bit soft but now that I am resolving the vacuum leaks it has gotten softer as the overall vacuum level of the system improves. I am thinking that the previous owner may have adjusted the modulator on the transmission to compensate for poor vacuum elsewhere. Now the transmission has too much vacuum and the modulator may need to be re-adjusted.

Does that make sense?

Bill
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Current Vehicles:
1990 Mercedes 300SE (147,000)
1985 Mercedes 300SD (203,000)
1983 Mercedes 240D (167,000)
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  #4  
Old 09-17-2002, 07:03 PM
Nate1954
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Hi Bill~
Yes, it could make sense....any way to ask the previous owner?

When I started trouble shooting my vacuum issues....I disconnected everything that "needed" vacuum and then took my reading.....I then started reconnecting devices and hoses one at a time to determine if I had a leak...."lost vacuum."

You can make assumptions all you want.....have you had the transmission serviced? What did it look like inside? New filter....etc.?

Nathan
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  #5  
Old 09-17-2002, 07:20 PM
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Join Date: Jul 2001
Location: Olathe, KS
Posts: 40
I don't know when the last service was performed on the transmission. Records from PO are non-existent. The fluid on the dipstick looks find - not burnt looking or smelling. Guess I'll change the fluid and filter this weekend and see how it looks.

Thanks for your help.

Bill
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Current Vehicles:
1990 Mercedes 300SE (147,000)
1985 Mercedes 300SD (203,000)
1983 Mercedes 240D (167,000)
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  #6  
Old 09-21-2002, 09:20 PM
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Join Date: Jul 2001
Location: Olathe, KS
Posts: 40
Thumbs up Fixed ! ! !

The transmission is now shifting like it should. I went through the adjustment procedure outlined in http://mbz.org/info/articles/trans/adjust/ and found that the vacuum valve on the IP was out of adjustment - not releasing enough vacuum as the engine speed increased. Adjusted the vacuum valve and changed the transmission fluid and filter. All is right with the world.

Thanks for your help.

Bill
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Current Vehicles:
1990 Mercedes 300SE (147,000)
1985 Mercedes 300SD (203,000)
1983 Mercedes 240D (167,000)
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