vacuum modulator disconnected?
 

Greetings all, newbie here. Great community of MB owners here, hope to be a long time member.

Got a problem I hope someone here can help me with. I recently purchased my first MB, a 1990 420 SEL. Absolutely love this car. First thing I did when I got her, as I usually do with a newly purchased auto, is changed the oil and looked her over really good. While under the car I found a vacuum line disconnected from what I think is the vacuum modulator (round, about 2 inches in diameter on the side of the tranny with one vacuum line attachment). Needless to say I connected the line and now I am having shift trouble. :eek: The tranny seems to be hunting gears, particularly between 3rd and 4th. It seemed to soften my shifts a little, more like a luxury car feel, but now it hunts between 3rd and 4th and sometimes between 2nd and 3rd. It seems to have a mind of it's own. I do not know how long it has been disconnected and when I reconnected it the car went back to normal (good shifts at right time albeit a little stiffer). Question is if this modulator (?) is diconnected can it damage the tranny? It runs and drives great without it. If there is a repair involved is it likely to be a costly one and can I drive the car without it being connected until I can get the repair done. I don't want to end up on the side of the road with the wife and kids if you know what I mean, but after just purchasing the car I can't afford a major repair bill either.

Forgive me if this is a little lengthy, I am not exactly Mr. Goodwrench however I want to make sure I give everybody enough info to help me out with this. Thanks for reading, any help is much appreciated. HD

Gosh, if the modulator is disconnected it should be jarring your teeth loose with harsh shifts.

No, not at all. It can be a little harsh if I get on it pretty good but normal driving it shifts a little like my wifes subaru. Not MB quality for sure but definitely drivable.

Anybody??
 

anybody know if having this line disconnected can do damage to the transmission?

Well, it certainly implies that the trans is running with very high pressures, perhaps set up that way to keep it from slipping.

Or maybe it's just a bad modulator.

It is something you should have looked at.

There is an adjustment after you connect the vacuum line you can adjust it right to decrease the air (rough shift) or to the left (slipping shift). You need once cycle to see the difference.

OK Thanks, I will reattach the vacuum line and make an adjustment. Will report back how it goes. Does anyone know if this may have caused any damage to the transmission? I don't know how long it has been unattached.

If the shifing was rough for a long time it will hurt but I don't know how, maybe it will damage the drums but not sure about it.

Check the transmission mount anyway.

Update: Adjusted the vacuum at the transmission 3 turns to the right (clockwise) and car is now shifting great. Thanks for all your help.