Rear Axle Differential Mount Replacement

[rwmastel]

Hi Group!  This weekend member Bill Rader came over and helped me perform two tasks.  Here is a thread on the first, and I will make another thread on the second.  Bill, correct me if I wrote any wrong instructions or descriptions!

Rear Axle Differential Mount Replacement

1. Ensure existing mount is bad.  This can be done visually by looking for space between the top plate and the mounting plate (against the body).  I had none.  This meeting of the plates causes a tapping or clunking noise as you drive over bumps.
Download Attachment: Bad Diff Mount 2.jpg
58.79 KB

2. Jack the rear of the car up by the differential.  This will push the differential mounting post up through the trunk and expose the problem with the mount.  I don't know if it could happen or not, but take care that the mount does not break loose and let the car drop down.  I can imagine the top plate and bolt hitting the soft top compartment.  Could this happen?
Download Attachment: fix mount 001.jpg
61.7 KB
Download Attachment: fix mount 002.jpg
63.06 KB

3. Place jack stands under the car where the trailing arms are mounted to the body.  These mountings look like triangle plates.  This allows you to push the differential up/down using a jack.  Remove the 4 bolts holding the differential mounting plate to the body and remove the main center bolt holding the mount to the differential post.

4. Remove the top plate from the mount.  Note the notch in the center hole because there is a pin on the differential post that matches this.  It must be replaced properly.  Pry the mount up and out of it's position.  You may need to work the differential up/down with the jack to completely free the mount from the hole in the body.  Some fine movement can be achieved by lifting, pushing, or pulling on one rear wheel.
Download Attachment: fix mount 003.jpg
55.61 KB
Download Attachment: fix mount 004.jpg
63.87 KB

5.  Place the new mount on.  The mounting plate is not square, it is a rectangle, so make sure you have it oriented correctly.  Again, some up/down movement with the jack or some rear wheel manipulation may be necessary to seat the mount properly.  Note how the base of the mount fits on the differential post.  Once seated properly, lower the differential enough to install the 4 bolts that mount the mounting plate to the body.  Once done, place the top plate on and install the center bolt.  Lower the car to the ground.  You will see the space created between the mount plates by the new strong mount.  With the tires on the ground, you can raise/lower the rear bumper and see the rubber mount working.
Download Attachment: fix mount 005.jpg
60.93 KB

6.  After a test drive of 5 minutes, you can see how the mount settled down some.
Download Attachment: fix mount 006.jpg
60.76 KB

This is not a bad job to do with two people.  One could accomplish it, but it's nice to have one person manipulate the mount while the second person manipulates the rear axle using the jack or rear wheel.

I hope this helps someone in the future.  It really helped my car!

Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both  tops
1994 E420

[pkiefert]

Rodd, you can post this in Technical Articles section also so it will be easier to find?

[rwmastel]

No, I can't.  I will ask someone else about that, though.

By the way, when you search using the search field on the home page, it searches the the whole site including the forum.  Using the search from within the forum only searches the forum.

Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both  tops
1994 E420

[n/a]

Rodd, this was excellent, and thank you for the thoughtfulness of the pics and the text posting.

Let me ask the following since I've read here and elsewhere that this improvement/refurbishment can affect ride hieght... do you agree and by how much would you estimate (roughly) such a replacement would increase ride height/differential position?

Not so Nervious (anymore) Newbie `68 280sl

[Bill Rader]

Brian,
This fix will not affect the ride hieght very much but it will help to stablize the rear end.Mine was so bad it came apart in my hands.I had noises coming from behind my head and the rear of my car would drift from side to side at high speeds. It made an huge difference and is a very easy fix.
Bill Rader
'68 250SL

[rwmastel]

Brian,
Sorry, but I did not think to measure that.  If it effects it, it would only be a small amount, like 1/4 inch or so.

Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both  tops
1994 E420

[merrill]

Rod,
what did you torque the diff mount bolts to?
the haynes manual indicates 87 fl lbs for the diff bolt but no recommendation for the 4 bolts that hold the mount to the car.



thanks
matt

[rwmastel]

Matt,

To what ever felt right.  Didn't know the torque rating and didn't use a torque wrench.  Just made them really tight!

Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both  tops
1994 E420

[merrill]

found it,
87 ft lbs for the diff hanger and 32 for the 4 bolts to the cross member.

[merrill]

Rod,
well, after thoroughly studying your procedure for changing the diff mount I tackled the job today.  i must be either lucky or have the wrong part because the old diff was removed rather easily and the new one just slipped in!!

all I did was support the diff, unbolt the old one, wiggle it out, wiggle in the new one and lined everything up, torqued the bolts and viola i was done.

thanks !!!

matt

[rwmastel]

Great!  I'm glad something I posted actually helped someone.  Did you notice a big difference in your ride?

Rodd
Powell, Ohio, USA
1966 230SL, Euro, Auto, Leather, both  tops
1994 E420

[awolff280sl]

I bought this less expensive diff mount made by Kratex or Karlyn. Made in Germany. There is no exposed rubber, the entire mount is encased in metal. Very stiff.





The MB part (below) has exposed rubber, and the center sleeve through which the vertical mount inserts is much more "flexible".





I think I will return the Kratex part. I'm worried that it is too stiff and that the vertical strut will wear the metal sleeve in the mount.