Trans Adjustment W115/300D '76
 

I have looked and searched but come up short on this one. I even have the shop manual which references linkage on some models, vacuum modulators on others, and so forth. I cannot find any linkage or even where it may attach at the throttle linkage if it were to be there. I can find no vacuum source either leaving the engine compartment or where it would terminate on the tranny. I'm not new to Benz and I've just replaced a tranny in one of my late 201's so I feel fairly comfortable that I can find my way around once I locate the adjustment point/points. I understand the relationship between load, shift timing, and shift firmness pretty well by now I hope. What I don't see on this engine is any vacuum regulating device to replicate the behavior of a gasser. That leads me to think that it is mechanically controlled via linkage but there is none. Am I as lost as I think?

There must be something regulating the shift points as it does not do a bad job at all. I do get a slight flare between 3rd and 4th when pulling up hills and no kickdown but otherwise it does well. What I'd like to do is firm up the shifting as is possible with the vacuum modulator on later models. Kickdown switch is dead but that's an easy one.


Any direction you folks could provide would be wonderful.

Thanks,
Sam

'91 190E 2.6 "Survivor"
'93 190E 2.6 Sportline "Treasure"
'76 300D "Slow Gin Fizz"

I know that early 123s (77-79) have a mechanical throttle pressure rod. The 300 is alot harder to get to than the 240. I would recommend looking from the trans forward and follow the rod to the engine. I just workd on a 78 300d and the linkage rod for the trans was buried. I believe it terminated on the inboard side of the inj pump. It hooked onto the transmission on the passenger side of the transmission. Hope this helps.

Will look this afternoon.
 

Thanks for the tip. If it's there; boy is it buried. The area around the injection pump is one that I have not concentrated on...thinking that surely it would originate over on the passenger side where the majority of the linkage puzzle is located. This car is a W115 chassis and is significantly older in design than the W123. From my experience, not much is the same between them aside from the OM617 lump itself but I'll give it a go over there and see what can be found.

Any more specific knowledge may save me a whole heap of time and a few busted knuckles;)

Thanks again,

Sam

I am reviving this old thread in hopes that you found the problem sam and know what control your trans.

I am stuck in the sam boat right now. Same car, 1976 300d. I can not figure out why it shifts so late from 1-2 and does not shift after that. Could it be a low vacuum issue?

The gas 114 115 have a mechanical linkage for sure. So the diesel automatics of this vintage will have one too.

The gentleman that posted his shift issues. Disconnect the switch under the throttle pedal in case it is closed all the time. I do not think it the issue but just in case. I am assuming it has one without knowing.

Other than this I suspect the seals are dried up from sitting in the transmission. Since this is not experienced as much on the 123 transmissions I suspect they changed the seal material at some point. Again without knowing.

Try some automatic transmission aid stuff. It functions by expanding old seals.Needless to say make sure your transmission fluid level is accurate.

There also is a small chance the transmission filter is shot. Other than these things the transmission would have to be rebuilt I suspect. The seal expander also takes time to work properly. Usually as much as fifteen hundred miles in a driver. Improvement by the seal expander of any amount will indicate what the trouble probably was. Dried out seals in your vintage actually are fairly common.

I have even seen a mechanical engine shift linkage rusted off on a 114 gas car causing very early shifts. I guess again without knowing had it rusted off in the other position the shifts might have been very late.

Sam:

If this is set upthe same as my 75 240d the control pressure rod id on the passenger side of the trans and engine . It runs under the exhaust manifold and hooks up to the throttle linkage.Make sure your getting full range movement out of everything there is no modulator on this model its controlled bythrottle movement.kickdown is by solonoid on pass side of trans.Good luck