WIS 22.10 Engine Mounts, Engine Brackets

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Issues - Engine Mounts

Many Mercedes-Benz owners experience vibrations through the interior of the car, the steering wheel and the seat which is the first sign that your engine mounts are failing or have failed.

BenzWorld Member zz4x4 reported that he had the very common "shaking at idle" issue so he decided to replace the engine mounts. It totally solved the problem! The car was smooth once again. The job went pretty smoothly and took about three hours total time.

Other M-B owners have reported having a smooth idle until you put the car into gear, then a vibration is noticed.

Diagnosis - Engine Mounts

Diagnose failed engine mounts by following these steps;

  • Park the car with the front pointing in a "SAFE" direction, ie with no one in front and a considerable distance from objects.
  • Open the hood.
  • Have someone apply the service AND foot brakes.
  • Stand in a position to the side of the car such that you can observe the engine movement. Do not stand in front of the car.
  • Ask the Helper to gently "REV" the engine on and off.
  • Observe how much rotational rolling movement there is in the engine.
  • Decide if the amount of engine movement is excessive. You will know what "excessive" is. If the engine was Rocking and Rolling SEVERAL inches up and down you have BAD ENGINE MOUNTS!

DIY Replace - Engine Mount Front

Tips - Engine Mount Front

  • WIS specifies removing the ENTIRE Engine Mount, both the engine mount AND the portion that connects it to the engine block. This worked fine on the RIGHT mount, but on the LEFT, a hose prevented taking the mount out/or installing, in one piece. This required a combination "Bottom-Side" and "Top-Side" approach.
  • Caution; when you turn the left engine mount over to remove the mount-to-bracket bolt, be careful of the fluid in the mount. If the rubber has deteriorated badly, when the mount is flipped over, the fluid can pour onto your face.
  • Even though genuine M-B mounts are expensive, the general opinion is to NOT buy aftermarket brands.
  • The original mounts on the Mercedes-Benz are made by Lemforder.
  • If a vehicle lift is not available, put the car up on jack stands and remove the front wheels for better access under the car.
  • Have a hydraulic jack available to support the engine and to lift it slightly during the replacement procedure.
  • Disconnect the battery before starting as you do not want to short out the starter motor connection etc.
  • Before you start purchase a long 40mm length M8 x 1.25 bolt to be used as an alignment tool. During the procedure you will be lifting the engine slightly after releasing both engine mount bolts. If you do not want to remove both engine mounts simultaneously in order to keep the engine perfectly aligned, thread the 40mm bolt into the bottom right side mount hole 2-3 turns. This allows the right side to stay aligned while lifting the engine and replacing the left side mount.

Method A - Engine Mount Front

An excellent write-up for replacing the front engine mounts on an S430 by BenzWorld Member zz4x4 is here; http://www.benzworld.org/forums/showthread.php?t=1388342

And is reproduced with minor editing here;

  1. Read the TIPS Section above before starting.
  2. Open hood and remove the air intake ducts to allow room to work.
  3. Disconnect the battery due to shock hazard working near the hot starter terminal.
  4. Loosen front wheel nuts.
  5. Jack up or lift vehicle to a moderate height that can allow access to the engine from the top as well as bottom.
  6. Support the vehicle on jack stands.
  7. Remove front wheels for better access.
  8. Remove the lower engine cover panel under the vehicle.
  9. Using a 13mm socket, remove both lower engine mount bolts and set aside.
  10. Using a floor jack or suitable lifting device, raise the engine via a piece of wood under the oil pan. The engine can be lifted about 75mm or three inches before the AC hoses begin to show signs of stress. TIP: Do not lift much further than this!
  11. Lower the steering rack about 50mm or two inches.
  12. Using a deep well 18mm socket, retain the nut inside the subframe channel on the two rear bolts. Using another 18mm impact socket or wrench loosen the two rear bolts. TIP: Do not fully remove the rear two bolts but make them as loose as possible while still keeping the nut on the bolt.
  13. Completely remove the two front steering rack bolts using an 18mm open end wrench and impact socket. TIP: This will allow the rack to hang down and move forward but still allow easy re-installation.
  14. Remove the upper engine mount bolts. TIP: On the V8, there is little room for a socket due to the exhaust manifold. With the engine raised it is much easier to do this step though. From the top use a 16mm ( or 5/8 SAE) ratcheting box end wrench and loosen the bolts. They will not come out due to their length, but the engine mounts will drop off the bolts when they are loosened enough.
  15. Remove the left side mount towards the front between the steering rack and subframe.
  16. From the bottom of the car, remove the right side engine mount rearward and pull out between the catalytic converter, bellhousing, and subframe. TIP: You may need to raise the engine a tad if it will not come out easily. It may take a little finessing and tugging to remove.
  17. Press the new mounts into the same areas the old ones came from. TIP: Get into a position under the car where you are supported and can hold the engine mount against the upper bracket with one hand and still reach the upper bolt with a couple fingers of the other hand. As you press the mount against the upper bracket, screw the bolt into the mount. Just a couple threads is all you need. Now spin the mount clockwise to tighten while keeping a finger on the bolt. After several spins, you will feel there is a place where the mount locating pin will pop into the recess on the upper mount bracket. At this point the mount will no longer spin.
  18. You can now go to the top of the engine and fully tighten the bolt to ~55NM. TIP: Tightening the upper bolt is much easier while the engine is still lifted.
  19. Reinstall the two front steering rack bolts / nuts and tighten all four bolts to spec.
  20. Lower the engine slowly watching for the engine mount threaded holes to stay in alignment with the subframe holes. TIP: If side to side adjustment is necessary use a crow bar.
  21. Reinstall lower mount bolts using Loctite and torque to ~35NM.
  22. Reinstall air ducts, lower engine cover, connect battery and your done!

Method B - Engine Mount Front

These instructions apply to Mercedes-Benz cars with the V6 and V8 engine.


DIY Replace - Engine Mount Rear/Transmission

A Rear Engine and Transmission Mount DIY replace is a super easy job. It actually takes more time to get the car lifted, as it does to R/R the mount, plus, as opposed to the "expensive" front mounts, the Rear is a measly $30 bucks.

Tips - Engine Mount Rear/Transmission

  • One suggested "variation" from the WIS technique is to not REMOVE the cross-member. You can loosen it sufficiently to get the mount in/out if you minimally (1 or 2 cm) raise the transmission pan.

Special Tool - Engine Mounts

A special M-B offset wrench/spanner is available to assist with replacing M-B engine mounts. See [1]