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  #1  
Old 11-06-2002, 11:36 AM
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Transmission shifting

I recently purchased an 84 300SD. It is a beautiful car with only 121K mi on it. It is absolutley cherry. The only problem that I have is a shifting problem. I took it in to a mercedes mechanic and he made a couple of adjustments and changed the trans oil and filter and said that there is nothing wrong but I disagree. The trans shift fine under heavy acceleration which is how he drove the car but under light acceleration it has several problems especially when cold. It has a very hard 1-2 shift followed by either a flared 2-3 under moderate acceleration or a double 2-3, 3-4 shift under light acceleration. Are there any comments on these problems? This is my first mercedes but I have considerable mechanical experience on tractors, cars and aircraft and want to learn the systems on this car. Also I have read that thr transmission manual is not available through Mercedes but there must be access to a manual somewhere. Does anybody have a source for this manual.

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  #2  
Old 11-06-2002, 01:25 PM
NIC
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congrats on your purchase.

Far as I can tell by experience and what I read, the 1-2 shift on these cars is normally very hard so that should not be a concern. Flaring on 2-3 and double shifts beyond that is not normal. There are several adjustments that can be attempted. I am not expert enough to explain them but if you do a search on this site you will find numerous discussions. Vacuum is the key and it can be somewhat tricky to deal with. Flaring on 2-3 can also be indicative of a more serious problem that is typical of these cars but which may not be fixable without a rebuild.

Sorry I can't be of more help.

Nic
300CD @ 154k miles
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  #3  
Old 11-06-2002, 02:47 PM
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Fly,
I had the exact same problem that you had with hard 1-2 shifts and flaring from 2-3 (or was it 3-4, one of those). Also, just like your car, mine did not exhibit those problems under hard or firm acceleration. My mechanic was able to all but eliminate the problem. I can still force the flaring if i drive it a certain way but for the most part, the problem is solved. I would bring it to someone else who may be more knowledgeable or try to adjust the vacuum yourself. The vacuum modulator is on the driver's side of the transmission and acts as a vacuum valve that regulates vacuum flow to the transmission. Try turning the valve in a half turn and then drive it around to see what happens. Whatever you do, make sure you only make small adjustments and then test drive to assess.

Alex
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  #4  
Old 11-06-2002, 04:51 PM
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Fly,
Try disconnecting the vacuum all together like Don suggested, but if it clunks when it downshifts (like when you're coasting to a stop) you might have to restore the vacuum and fine tune it. Having no vacuum firms up the shifts so that they are abrupt. I like this under normal driving but the clunking while downshifting is rather disconcerting. I have found that you can only reduce the vacuum to a certain point to keep it shifting relatively smoothly. Good luck

Alex
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2012 VW Sportwagen TDI Manual
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  #5  
Old 11-06-2002, 05:46 PM
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Fly:

Your talking my language. Identical problem. Here is my advice to date:

1. You have too much vacuum under light acceleration. This is most likely due to wear in the tranny plates or the vacuum bleed valve (white) which sits atop the IP on the rear.

2. You can disconnect the vacuum line which runs from this bleed valve and goes to your vacuum modulator under the car. This will in effect deliver no vacuum to the tranny. See what happens as this is the normal vacuum rate under hard acceleration. In other words, with the vacuum line disconnected, you'll have the same setup as you do under full acceleration.

3. My car functions well and shifts well with no vacuum period. So I'm leaving it there. I can deal with a normal harder 1-2 shift. It was the flaring which really concerned me.

4. If you want perfection, do two searches under this forum:
A. Under "diesel don" called "transmission flaring" and
B. Under "larry bible" called "i hate automatic transmissions"

5. Under Larry's post, I referenced two phenomenal articles written by pros complete with pictures and 5-6 options for adjustments. These adjustments will be far more sophisticated than a local MB tech will even know about. This Steve Brotherton who wrote one of them put 5 pages out (single spaced) on this adjustment alone. The guy is a legend.

Don
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DAILY DRIVERS:
'84 300DT 298k (Aubrey's)
'99.5 Jetta TDI IV 251k (Julie's)
'97 Jetta TDI 127k (Amber's)
'97 Jetta TDI 186k (Matt's)
'96 Passat TDI 237k (Don's
'84 300D 211k Mint (Arne- Undergoing Greasecar Conversion)

SOLD:
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  #6  
Old 12-03-2002, 05:44 PM
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I have tried to find the post by Larry Bible titled "I hate automatic transmissions" and the search comes up blank. Anyone have a link to this or know where it is? Thanks, RT
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  #7  
Old 12-04-2002, 09:26 AM
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LarrryBible doesn't have a space in his user name.

Here's the thread:
'81 300D modulator?
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  #8  
Old 12-04-2002, 06:11 PM
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Got it and printed it, thanks much! RT

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