Hi Folks,

I have an 88 300SEL that I've just purchased not too long ago. I know the motor mounts are bad (been told by two shops), and I am aiming to have them fixed next week. I'm curious though.. when the motor mounts are bad, would that create a low-pitched "rolling" sound when I accelerate? I don't really notice any vibration from the motor, just this sound when I start off which I'm hoping is because of the mounts. My fear is to tell the shop I hear this noise, and let them have at it trying to figure it out.

Anyone have an idea as to what exactly happens when the motor mounts are bad?

Thanks much,
Craig

Yes, it can create a moaning noise, often it is "felt" more than "heard", kind of a moan and vibration noise together.

Gilly

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Thanks for that information Gilly. Would you happen to know what the shop should be charging me to install the new ones? I'm going to a new shop, and I hate to be taken. In terms of hours, would about 3 hours be needed to install new motor mounts? More, less?

Thanks Gilly!!

It's not too bad of a job on the 300SEL, I'd say they are a little high on that, but not terrible. A couple hours should be more than adequate, but if you've been there before and have been satisified with the work and generally happy with the shop, I'd consider letting it slide. The "book" time may very well be that high on it.

Gilly

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I did mine this weekend ( never done em before ) made one mistake ( had to remove more than needed ) but in all took me about 4hrs. I'm sure i can do it in 2-3hrs next time.

I've replaced 3 mounts on the passenger side, they seem to collapse much faster than the driver side, due to the exhaust heat and the engine torque pushing on them, I suppose.
Passenger side takes about 15 minutes after doing it 3 times, but the driver side is MUCH harder to reach. 2-3 hours flat rate is probably correct - but if they're experienced, they will do it in one.

I developed a Special Measurement Technique for the passenger side mount, to tell if it was collapsed too much. There should be a small sheet metal heat shield over the mount. If you cannot put your index finger between the shield and the mount bracket, the mount is just about ready for replacement.
I wonder if real MB mounts are any better than the aftermarket ones?

I also get that little rumble on acceleration in first gear - seems like a u-joint. Could it be the slight mis-alignment of the center carrier bearing as the engine settles due to to the collapsing mounts?
The most common noise asociated with right-side mount collapse is the banging of the exhaust pipe on the cross brace. It begins first when you accelerate while turning left - very easy to diagnose, sounds like a hammer banging under the right floorboard.

Have them check the rear tranny mount also - they don't collapse near as much - but it's good to look it over - and easy to replace.