85 280SL euro transmission hard shifting. - PeachParts Mercedes-Benz Forum

desert · #1 07-28-2009, 09:04 PM

My 1985 280SL Euro, 55k on it with auto trans is starting to shift up hard between gears, it's always made you aware that it was shifting but now it can snap you back going from each gear. It does it more when it's cold although right now it's way over 100 degrees here in Arizona but sometimes it still does it when it's really warmed up. First, any ideas why it's shifting so hard ( oil level is fine and oil is clean) and second can you tell me the model number of this transmission that is married to the streight six engine in the 85 Euro 280 SL. Thanks for any advise. Desert

tecqboy · #2 07-28-2009, 11:39 PM

possible bad vacuum modulator. Do a search.

desert · #3 07-29-2009, 10:38 AM

Thanks for the info. I'm reletively new on this forum so what do you mean by "do a search" and how do I do that?....Desert

tecqboy · #4 07-29-2009, 10:42 AM

Go to the very top of this page and press the search tab. Fill in the blank with the term you're looking for.... like : Vacuum modulator.

desert · #5 07-29-2009, 10:56 AM

Thanks, that works great and lots of good info there...Desert

desert · #6 07-29-2009, 11:19 AM

I've gone through what I think are the applicable search topics and I still can't find out what model transmission is mated to the 110 engine in my 85 280SL Euro. Is it the same as a 85 American model 380SL? I kinda doubt that it is so any info along these lines would be appreciated. Also, any recommendation where to buy a vacuum modulator for this transmission? Thanks, Desert

desert · #7 07-29-2009, 05:22 PM

I did some further research myself on this and found out the 85 280SL Euro has a model 722-306 transmission which is rather rare. Thought this may be of some interest to owners of simmilar Euros. Thanks to all for the input.....Desert

tecqboy · #8 07-29-2009, 09:16 PM

OK. A little research goes a long ways. But, don't just change out the modulator valve without first determining if the vacuum system is functioning correctly; that is, no leaks. When cars get this old, the rubber hoses and even the metal ones go bad. Plastic couplings break and seals leak. Lots to go wrong. Tracking down vacuum leaks requires a small hand held vaccum pump.

There are basically 2 places leaks occur; along the vacuum line from the manifold to the modulator, and/or the modulator itself. To test, a tech puts a T valve at the modulator and connects one end to the vacuum line, one to the modulator and the last to a test line and guage that reads the vacumm pressure while the car is test driven and watches for drops in pressure. If the pressure holds on the line, it's most likely the modulator.