Aging Motor Mounts?
 

I have a '99 C280 with 201,000 miles and have noticed recently that the motor vibration has become more significant. While not broken, can motor mounts "harden" and in effect, transfer vibration and noise to the chassis and the passenger compartment?

Yes.

Difficult to replace?
 

Dave,

How many are there and are they difficult to replace DIY?

Brad

Motor mounts typically collapse over time. The rubber "sandwich" tears or collapse, allowing motor vibrations to transmit to the frame. Usually, there are two motor mounts. You may also want to inspect the transmission mount for the same condition.

There are two mounts. I dont have any experience on your models car so I cannot say how difficult it will be to get at them. I have always had to use tools that are optimized for hard to get at spaces to get the bolts out. Typically they are not the easiest things to replace.

i dont know about benzes, but i know motor mounts are something i never want to do again and i would have an indy do them anyday.

You have two gel filled mounts. They split and leak out the glycol gel, and the engine shakes.

Replacement is fairly easy if you can get to them. I'm not familiar with that model, but there is most likely a bolt top and bottom, the mount itself is a fairly large metal and rubber item about the size of a softball.

To replace them, you have to jack up the engine a few inches and remove the upper and lower bolts. Top is likely a 19mm hex head, the bottom is likely an 8mm cap screw (Allen head). Lift engine until you can get the mount out, then jack another inch or so so the new one will fit in (maybe more!). They are indexed with a pair of ridges on top and only fit one way, make sure they are in correctly, then tighten the bolts. Watch that you don't drop the bottom screw into the frame, it's a bear to get out.

Best to use an engine hoist and the lift eyes or a floor jack on the oil pan with a board between to lift the engine.

The main difficulty is reaching the top bolt on some models. V8 engines and turbodiesels really cannot be reached from the top.

Peter

BPH - take a look at this thread on mounts:

BPH- I replaced the motor mounts on my 90'420 SEL 171,000 just last month and they were as flat as pancakes, after they were replaced the engine rose an inch! Before hand the car would vibrate so much in park I felt like a milkshake! No vibration what so ever now. There are three- two for the engine and one for the transmission.