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Rear Engine Transmission Mount Replacement
 
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Pelican Technical Article:

Rear Engine Transmission Mount Replacement

Tom Morr

Time:

1 hour1 hr

Tab:

$25 to $60

Talent:

*

Tools:

Floor jack, torque wrench, 13mm, 16mm ratchet and sockets, 17mm wrench

Applicable Models:

Mercedes-Benz SLK230 (1998-04)

Parts Required:

Transmission mount

Hot Tip:

Support the transmission with a floor jack.

Performance Gain:

Corrects annoying vibrations in the cockpit.

Complementary Modification:

Inspect driveshaft flex discs, replace if necessary.

Rubber isn't forever. Oil, ozone, heat and vibration degrade it. The R170 SLK's transmission mount is a prime example of an important part that eventually suffers from rubber failure.

A bad transmission mount (sometimes referred to as the "rear engine mount") not only transfers drive train vibration into the cabin, it also causes driveshaft misalignment, accelerating component wear.

To begin you must raise and support the car. Please see our article on jacking up and supporting your vehicle.

An automatic transmission is shown here but steps for a manual transmission are similar.  The process is reversed to install the new mount.

Torque specs:

Mount to Transmission - 40 Nm / 30 ft-lb

Mount to Crossmember - 25 Nm / 18 ft-lb

Crossmember to Car - 40 Nm / 30 ft-lb

Once the car is raised and secured, the transmission's weight must be supported.
Figure 1

Once the car is raised and secured, the transmission's weight must be supported. A floor jack can be used to support the transmission, either under the bellhousing or combined with a piece of wood to distribute the load across the transmission pan. The jack's pad will deform the pan if wood isn't used. On the R170, the transmission cross member is secured to the car with three 17mm-head bolts on each side. Two of the bolts have already been removed (green arrows).

Two 13mm-head bolts secure the transmission mount to the cross member; loosen these.
Figure 2

Two 13mm-head bolts secure the transmission mount to the cross member; loosen these.

The cross member can theoretically be lowered on its bolts, but we took it out to facilitate photos.
Figure 3

The cross member can theoretically be lowered on its bolts, but we took it out to facilitate photos. Lowering it on its mounting bolts normally creates enough space to access the transmission mount. However, removing the cross member improves visibility for inspecting the drive shafts front flex disc. On the right side, an exhaust bracket impedes socket access to the center cross member bolt. A 17mm combination wrench can be used, allowing the exhaust bracket to remain in place. The mount mates to the transmission with a 16mm-head bolt on either side. The mount's ears are angled with their tops facing the car's rear. If the mount is flipped, its base won't sit flush on the cross member.

The transmission mount has a steel structure that's isolated by vibration-absorbing rubber.
Figure 4

The transmission mount has a steel structure that's isolated by vibration-absorbing rubber.

The SLK's cross member aligns with the mount's center holes (green arrows).
Figure 5

The SLK's cross member aligns with the mount's center holes (green arrows). The process is revered to install the new mount.

This mount is fine.
Figure 6

This mount is fine. However, its rubber will eventually crack and decay. The ensuing metal-to-metal contact transmits vibration to the interior and accelerates driveline wear.

Transmission mount replacement is an easy DIY job.
Figure 7

Transmission mount replacement is an easy DIY job. These tools plus a floor jack and torque wrench are all that's required.

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Comments and Suggestions:
SLK230London Comments: I've read the above article and wanted to tackle the job myself. I'm not tried this before, but I'm able to change brake pads and disc, service a car etc. would this be easy for a first timer? I've got all the tools required.

Also, is it better to start on the driver side, then the passengers side, followed by the transmission mount? or doesn't matter? cheers
January 9, 2015
  Followup from the Pelican Staff: If you can replace brakes, you should be Ok with this. However, you are the best judge of your ability. It doesn't mater which side you begin with. - Nick at Pelican Parts  
Rusty Comments: Thanks for the torque specs Nick.
Roger
December 17, 2014
  Followup from the Pelican Staff: No problem:

Torque specs:

Mount to Transmission – 40 Nm / 30 ft-lb

Mount to Crossmember – 25 Nm / 18 ft-lb

Crossmember to Car – 40 Nm / 30 ft-lb
- Nick at Pelican Parts
 
Rusty Comments: You know, this is just a great source of Information for Slk owners. The pictures and simple how to info makes most work a "yes I can" or "no I can't" proposition.
Much appreciated.
Best,
Roger Mursick
December 14, 2014
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
 
rusty Comments: Nick...Thanks for that.
Best
Roger
April 4, 2014
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
 
Rusty Comments: This is great! And much appreciated. Can you please tell me the torq specification for the mount?
Roger
April 2, 2014
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help. I will do my best to get the torque specs added to the article.
- Nick at Pelican Parts
 

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