ello ,
There are a few different things that have potential to be the root of the vibration in your car....First off, I agree with the dealer replacing the transmission mount first.....this is very,very common on this body style s class.....but, they should have made sure it was fixed before giving it back to you....The catalytic converters are known to break apart internally and can cause a light throttle vibration(in shifter area) as well as an audible noise(grinding/clacking)....these usually will do it on deceleration as well....but can be intermittent, and are usually not speed related.....one other simple thing to eliminate are the shifter linkage bushings, they dry rot and fall off of the linkage and many times I will have a car show up at the dealer with a similar vibration(grinding noise) that will definitely be felt through the shifter.....and this can sometimes show up at a certain "speed" or engine rpm, and not be there at other speeds....Also could be just the rear tires(not the fronts,because it would be very noticeable in the steering wheel) being out of balance.....should have the dealer "road force" balance the rear tires(if you just bought the car and don't know the history of the tires...i.e. how long the car sat for sale, maybe they are flat-spotted...and its only showing up at these speeds)...a road force balance would show high numbers if this was the case.....Another occasional fix for something like this is to loosen all of the exhaust brackets, engine mounts, and cross member...then let them settle and re torque....Have seen this fix a lot of out of the ordinary vibrations/noises....Now, that we got the simpler solutions out of the way.....I did a MB technical search on the MB dealer only database for "technical specialist needed" repairs "cases" for vibrations on S500 4-matics....there are many "cases" that came up and not one specific issue that I can say was a majority....these include internal transfer case vibrations, front axle shafts, main driveshaft, and even internal transmission vibrations.....and unfortunately, these were all speed related (like yours), where the issue is there at a certain speed and gone at another speed.....so this is going to be very difficult for be to absolutely pinpoint what your issue is, without physically being in the car and under the car looking/working on it.....But, I will tell you that I have done several sets of engine mounts on S classes and it would be very rare to feel an "engine mount failure" only at a specific speed range.....usually can pinpoint these easily with the car in park and revving the engine quickly to 3500-4000 rpm, it will be felt through the undercarriage....Also, if I had to pick out one item, from the "bigger, more expensive repairs that I previously mentioned", that may be causing your issue.....it would be the transfer case....MB has always had different issues with these ever since they started making 4 matics....I have replaced more of these than anything else on 4-matics for a vibration(usually for a shutter when turning though)......well, good luck and I hope they can pinpoint it for you this time.....Bob
