W124 1987 230E , M102 engine

Hi all
Problem: Car shook when drive was engaged and when stopped at lights etc. The shake felt like a clutch slipping in a manual, but it's an auto. Could feel a bit of vibration in steering wheel and driver’s seat when driving at 50--60mph (3000 rpm). It varied in intensity from barely noticeable to 'change, light, go green now, get me moving again!'

Car starts easily. Engine idles smoothly and consistently in park and neutral. Reverse engages smoothly and quickly, and drive engages quickly. Shifts smoothly when rolling, engine runs smoothly on the go. So perhaps not fuel or spark, or tranny.

I’ve done some searches on this site and the symptoms led me to the engine mounts. Inspected mounts from below using a torch (flashlight) and they were cracked. Pushing on the valve cover from the side, the force was transferred straight to the chassis and front of the car shook. To confirm, went to garage, got the car up on a hoist and the tech could see too much movement with engine running and car in gear. So, mounts bad. Could be the transmission, but why assume the worst?

There are excellent posts on this site which I used, and Haynes manual as well. Here’s what worked for me:

Replace engine mount on one side, then the other.
1/ Soak all bolts with penetrating oil a couple of days’ prior
2/ Front of car on jack stands, handbrake on, rear wheels chocked, bottom engine cover removed, air cleaner removed
3/ 4x2 wood under oil pan, loosen fan shroud, jack engine up
4/ from below, unscrew allen head bolt (8mm hex bit) being careful not to drop into crossmember (don’t ask how I know a small magnet taped to wire is useful here...)
5/ from top, unscrew 17mm bolt
6/ remove mount and replace, checking alignment against notch on engine-to-mount bracket
7/ loosely rescrew allen head bolt from below
8/ slowly lower engine and loosely rescrew bolt from top
9/ lower engine, tighten bolts, then repeat on other side
10/ torque upper and lower bolts both sides, 54nm top, 40 nm bottom (Haynes specs)

There were a couple of hitches. First, a frozen allen head bolt on the underside of the old engine mount. Couldn’t get enough leverage with my Gorilla Grip allen key set, so I got a spare 8mm allen key, cut the short end of the ‘L’ off with a grinder to make a hex socket by inserting it into an 8mm socket. Applied force, the socket split and the bolt stayed frozen. Went and got an impact driver and inserted my 8mm allen bit: bang, bang, bang, hallelujah!

Second, the top engine mount bolt under the intake manifold was difficult to get at. Took a while to work out the best way given the very limited space and tightness of the bolt. Removed air cleaner. Used a ½ inch universal joint bar, a long extension and a flexi-socket attached to a 17mm socket. The best angle I found was to go in with the extension just above the power steering fluid reservoir. Avoiding hoses, wires, and without leveraging off the intake manifold, I got enough downward force to keep the socket on the bolt as I got the first movement and initial loosening. Switched to a 17mm ring spanner, then back to the flexi-socket and extension with ratchet for final unscrewing.

To finish the job, air cleaner back on, underside cover back on, fan shroud reattached a little higher, removed jack stands, lowered the car, started, put it in gear and ... ah! welcome back the Mercedes of old. No vibration. Smooth idling in gear. No shaking while stopped at red lights. No vibration at speed. When pushing valve cover from the side engine moves a little but movement not transferred to chassis.

For this job, if all goes well and the bolts unscrew OK you could get it done in an hour or two if you have all tools to hand. Took me longer, but the results are quite amazing.

Cheers
John

Thank you for sharing the information.

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