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Old 08-03-2005, 03:24 PM
Registered User
Join Date: Aug 2000
Posts: 17
300sdl transmission problem

My 300sdl is a 300k+ mile car and the transmission is not shifting properly.
I bought the car 50K miles ago at auction so I only know history via
inspection. I suspect the transmission is original. With that backround - the
tranny doesn't shift into 4th gear. Here's what's been done:
- filter and fluid about 10K miles ago, fluid was good then, and still appears
as it should. Also passes the smell test.
- Tried Trans-X 200 miles back - no change.
- Ruled out bowden cable and kickdown switch.
- Checked all vacuum lines for leaks / have not hooked up a vacuum tester.
Now for some additional symtoms. If the car sits for two weeks or so - the tranny will shift into 4th. Although as opposed to the robust / solid shift of the
prior gears- I'll say it sliiiiiides into 4th. The car will shift fine for 20 miles or so,
then I lose 4th gear. If I keep driving - I'll go another 10 miles or so then I'll lose 3rd gear. I havn't pressed my luck past that. I suspect I'm in for a major
rebuild - but would like to have some idea what's causing the problem.
Any help would be greatly appreciated.
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Old 08-03-2005, 04:17 PM
Hit Man X's Avatar
Join Date: Sep 2004
Posts: 8,976
Thumbs up

Well over 300k miles is quite a feat for an automatic transmission that's nearly 20 years old. I'd get ready for a rebuild honestly, but there's a few things you could check out prior to doing so.

The modulator on the case (driver side I recall) could be the problem. You could try pulling those vac lines, cleaning them, and reinstalling too. I believe new modulators are around $35-50. Just a few other things before throwing in the towel.

Hope it helps.
I'm not a doctor, but I'll have a look.

'85 300SD 244k
'87 300SDL 251k
'90 300SEL 325k
'91 560SEL 189k

Eight others from IH, BMW, GM, Ford, and Volvo.

Liberty will not descend to a people; a people must raise themselves to liberty.
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Old 08-03-2005, 08:16 PM
Johnhef's Avatar
Senior Member
Join Date: Feb 2005
Location: Frederick, Md
Posts: 4,540
try this: 300SDL Engine/Trans vacuum or Trans sticking?

connecting the vacuum lines back correctly actually fixed my problem. Check that valve on your IP though.

1980 500SE/AMG Euro
1981 500SEL Euro
1982 380SEL
1983 300TD
1983 500SEC/AMG Euro
1984 500SEC
1984 300TD Euro
1986 190E 2.3-16
1986 190E 2.3
1987 300D
1997 C36 AMG
2003 C320T 4matic

past: 1969 280SE 4.5 | 1978 240D | 1978 300D | 1981 300SD | 1981 300SD | 1982 300CD | 1983 300CD | 1983 300SD | 1983 380SEC | 1984 300D | 1984 300D | 1984 300TD | 1984 500SEL | 1984 300SD | 1985 300D | 1986 300E | 1986 560SEL | 1986 560SEL/Carat | 1987 560SEC | 1991 300D 2.5 | 2006 R350
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Old 08-03-2005, 09:00 PM
Registered User
Join Date: May 2005
Posts: 992
i had the same problem

i had 83 300 sd tranny problems and i could not figure it out so i
disconnected the vac to the tranny.... and stuck a stick in it...
at the valv ontop of the fuel pump....

and the problems went away.... so i need a new vac control for the shift...

try this.....
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