Transmission "slipping" into 3rd? 84 300SD w/153K
 

I am/was considering an 84 300SD with 153K. Odometer shows 153K, but I am thinking it is a little more, considering some things. The engine sounds fine (except for a little louder than others I have heard clack sound) and the power seems great for a diesel. A little slow starting out, but fine after some RPMS gain. The transmission had a firm 1-2 shift and even 2-3 at times, but at other times, it is like it kind of slowly "slips" into 3rd gear. I have postponed buying it because of this. I would think that a "well maintained" 300SD should have a transmission lasting longer than 153K. The A/C still works fine believe it or not. Everything seems to work except for the passenger side window will not go below an inch and the driverside door will not lock unless the door is shut. Body is 100% rust free- even on the jack points, but the original paint is peeling and fading on the top and hood. Has the typical cracks (2) on the dash board. Needs tires soon. They are asking $2000 for this car. The car is a dark gray color. The woman said that they have owned it for 2 years and it was a 1-owner car before that. The engine seems to "clack" a little louder than some other 300SD's I have seen, but I think it is OK. I did see some drips of oil under the car as well. Any advice/information appreciated.

No, I did not run a complete Carfax on the car to check the mileage. I know for a fact it has not been wrecked, as the paint is definitely original.

It's kinda hard for us to give you advice over the Internet on this situation, because it could be anything from slightly dirty transmission fluid to a situation requiring a complete transmission build.

So if you buy the car, you're taking some risk that the transmission will require replacement or rebuild.

Having said that, the symptoms sound a little like modulator adjustments and a change to fresh synthetic fluid would resolve the problem.

It would have to be in excellent shape otherwise to pay $2000 for it though. Market price on a nice 82/83/84 300SD with no rust, some body dings, good paint is no more than $3000. Naturally you pay more for cosmetics closer to mint.

You can probably resolve the problem without a transmission rebuild, but you're taking that risk. Based on that risk I think you should consider if its a car worthy of a $2000 value.

Ken300D

As I am learning with my SL (same basic trans), this is a well-known problem. It is more challlenging in the diesels, apparently, because the vacuum to the modulator needs to be simulated, since the engine itself does not create the vacuum that gas cars use to control the transmission.

I am not making this up.

Steve B has an excellent article on this on the web.

http://www.babcox.com/editorial/ic/ic20242.htm

There are also kits for the valve body to help fix this problem.

http://www.bulkparts.com/MM007.ASP?pageno=1200

And Mercedes sells a rebuilt valve body for $340. Neither of these solutions requires the trans to come out.

FWIW, we had an '82 300D (turbo) for many years and it would periodically do this. We would get an adjustment and it would be OK for a couple of years.

Yes, to give an example on the 1982 300D, I had a cold-weather flare on the 3-4 shift. Sometimes it was just not going to go in 4th gear. Once warmed up it was fine.

This was resolved by switching to synthetic ATF. Its cold-weather properties are better and I feel it helped to clean out the valve body too. Possibly I had a sticky valve controlling the 3-4 shift.

Ken300D

Thanks for the replies. It seems like it may not be too serious from some of these replies, if it is indeed the fluid. It may not be bad compared to other Mercedes, but it may be where I am used to the silky smooth shifting the my 90 Lexus LS400 has. The shifts are barely noticeable, so the Mercedes may be why it seems so noticable to me.

I have found another Mercedes that I want to also check out first, before I make any decisions.

Thanks again.