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Old 12-06-2003, 10:46 PM
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Join Date: Feb 2003
Location: New York
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85 300TD cold weather trans thump

I sometimes experience a clunk when I slow down from my trans. This only seems to occur when the temp. gets below 40 deg F. It used to happen often until I found a leak in one of my diaphrams under the dash. Could this be a vacuum problem or do you think it may be something else. I was thinking of a faulty modulator valve? Thanks.... PS all my locks work and I don't have the problem when the wather warms up..
85 300TDT 456,000 orig. miles
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Old 12-06-2003, 11:29 PM
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Join Date: Jan 2002
Location: New Jersey
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I notice the same exact thing... All my vacuum system is fine, as far as I know. I actually think it has something to do with ATF. I had it changed last time and they used quaker state ATF, the variety that says its good for Euro cars (thats what the indy uses). I think maybe its a bit thicker and so is a bit harsher to shift. I am going to have it changed by the MB dealer soon to see if that makes any difference at all (the fluid has only 20K, but it seems a bit foamy lately, so I want to change it out).

Ill update if that makes any difference, once I have it taken care of.

I also notice that there is a bit of a clunk from the rear end sometimes, especially if feathering the throttle on and off while going real slow at low rpm. Dont know if its related, but it only really shows up in the cold as well.

1981 240D (73K)
1982 300CD (162k)
1991 350SD (113k)
1998 Chevrolet S-10 ZR2 (62K)
2011 BMW 135i cv (14k)
2014 Honda Odyssey (6k)
2015 Honda Accord Hybrid (5k)
2008 VW Rabbit (70k)
2004 SAAB 9-3 (83k)
1991 BMW 318i (183K)
1983 300D (228K) (wrecked by at-fault uninsured driver)
1985 300D (233K) (now in FL)
1994 Acura Integra (188k) (Rusted out)
1992 Toyota 4Runner (72k) (Rusted out)
1990 Daihatsu Rocky (??) (No parts)
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Old 12-07-2003, 10:17 AM
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Join Date: Feb 2003
Location: New York
Posts: 161
In my case I'm not sure about the ATF fluid. It sometimes happens even after driving for a few hours which would lead me to believe theat the ATF fluid is plenty thinned out by then. I've had the same clunk in the rear now for the last 250k. It doesn't seem to get any worse though. PS I don't reccoment you go to the dealership, unless you have money to burn!!..
85 300TDT 456,000 orig. miles
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Old 12-07-2003, 04:26 PM
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Join Date: Feb 2003
Location: New York
Posts: 161
I have a mity vac. How do you set it up and whats the ideal reading to the transmission. Thanks
85 300TDT 456,000 orig. miles
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Old 12-07-2003, 05:27 PM
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Join Date: Jan 2002
Posts: 18,355
Turn the heater off by pushing the far right button on the control. If the condition improves, you have a vacuum leak in the heating system somewhere. If it doesn't look elsewhere. Could be flex disks but you need to exclude vacuum leaks. Ideally, you can tap in a Mity Vac and monitor the vacuum to the transmission as you drive.
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13
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