The car is a 1988 W124 that vibrates and clanks when turning over and then when in idle (especially with foot on the brake and car in drive). I've read a lot about motor mounts and i've checked them. They look good, firm, the height is perfect on them, i don't think the motor mount is the problem.

In addition the front of the engine has dropped for some reason. The crank pulley is now touching the housing for the fan of the radiator.

It's noteable that the idle is actually quite stable at 700 rpm, it drops maybe to 600 when i put the car in drive and keep my foot on the brake, but it doesn't vary or move. Also, when the car is in motion it's nice and smooth, the problem seems to be at a stop and on startup.

I'd appreciate any help, and thanks in advance!

The first question I would ask is: How could the front of the engine drop if the mounts are okay??? I think the dimension to check mount health is no less than 13 mm measured from the bottom of the widest part of the mount to the cross member. If the crank pulley is interfering with the fan shroud then the engine must have dropped.

The other suspect would be the exhaust system - heat shields, body clearance, and catalyst bed.

Duke

If the front has dropped, has the rear risen?

If the transmission mount fails, will the engine and transmission pivot around the engine mounts? You might check the transmission mount.

Best Regards,
Jim

I checked the engine mounts the dimension you are talking about duke is 15 mm on my car.

And yes, i would imagine if the front has dropped it could be that the rear has risen.

What should the distance be between the crankshaft pulley and the radiator fan housing?

It sounds like the lower radiator support may be bent. I have seen many of these cars where someone has hit a curb or something and it bends the lower radiator support up and back towards the engine. The easiest repair is to use a porta-power tool to push the support back to its original position.

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Mercedes Benz Master Tech - Retired

Clanking on start-up and vibration at idle are exactly the symtoms I had when the motor mount (right front) was bad on my '92 300e.

A bad motor mount is not very obvious to the eye and I was not convinced that was my problem until I replaced it and all the problems went away.

I have to agree with the above poster you really can't tell that the motor mounts is bad anymore. If those are newer motor mounts they don't collapse like the ones put on the car in the 1980's did.

But maybe youve tested this already but..With the car in gear and the brake holding it give it some gas and see if the engine twists.

The only other thing would be to get the car up and painstakingly go through things like the tranny mount, drive shaft mounts and bushings, etc, etc