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#1
12-30-2004, 12:42 PM
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80 300 SD harsh upshifting
Poor Soul has had a harsh upshifting problem since getting this chariot about 7 years ago. This problem happens mostly when upshifting from 3 to 4 and only when there is no load on the drive train. When loaded all shifts are nice and smooth. Engine is from an 81 D with less than 50K at time of change by a shop.Matching transmission that I later had rebuilt by a good tranny shop. Attempts at remedy are: Change of driveline including bearing,flex disks,differential,and drive axles,all from my parts car.No change at all.
From reading various threads,I surmised that the tranny modulator valve was getting some bad vacuum information. I found that the line going to the tranny was coming directly off the #2 inlet of the vacuum manifold coming off the vac pump. Should not the tranny line come off the output of the throttle valve on the valve cover? Does anyone have a diagram of the vacuum hookup in the engine compartment? I have been having vacuum problems with door locks,climate control and engine shutoff. Now mostly resolved except A/C compressor pump doesnt come on. Perhaps it is time to make sure everything is connected where intended. Anyone have that diagram they could email me at Tinwillie4128@yahoo.com? Poor Soul would be forever grateful. Willie 
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#2
12-30-2004, 09:28 PM
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Not really my area, but we had a diesel for a long time, and I will see if I can locate the vacuum diagram. Meanwhile, here is a pointer to a very interesting article by Steve Brotherton that explains how MB uses vacuum in a diesel car (no natural vacuum) to control shifting.
Good luck http://www.babcox.com/editorial/ic/ic20242.htm
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Chuck Taylor Falls Church VA '66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe
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#3
01-01-2005, 01:25 PM
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Chuck: Thanks very much for pointing me toward that fine essay on the transmission vacuum issues. I will have to make some of the tests he specifies to see what the vacuum numbers are for idle and full throttle conditions as far as vac to the tranny modulator. Since my car is a 1980 300 SD but has a 81 D motor and transmission ,I expect that I should be looking for a 81D engine compartment vacuum diagram. Anyone with input on that issue? I have resolved all the vacuum issues as far as heating,AC,auto locks and engine shutoff. Thanks and Happy New year to all.
 Willie
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