Bad Differential Mount? Rear end drops
 

Just noticed today at lunch that going from N to D and back and forth that the rear of the car must drop at least an inch, perhaps more.

My searching of the forums indicates that this may be the issue, but input would be a great help.

Depending on the idle speed, the response of the body is typical due to the applied torque.

When you shift to reverse, the back end of the vehicle will climb accordingly.

The diff mount might be tired, but it usually doesn't contribute to this phenomena because, although the rubber may sag, it's still relatively rigid.

You ought to check the diff mount anyway because they definitely do get tired due to the constant load on the rubber. I've got some photos in the archives that show the new mount versus an old one.

Thanks Brian. Do you have a URL to the photos?

Rear sag, if this is your issue, is caused by many issues. Diff mount, subframe mounts, and tired springs.

I rebuilt the rear on my 300SEL late last year and the car rides completely different without 250,000 mile springs under it. I have been telling people for years that these springs, like other cars, simply wear over time and are a large contributor to rear sag.

This thread has pictures of new and old diff mounts.

http://www.peachparts.com/shopforum/showthread.php?t=60587

I simply jacked the body up,and slid two large bolts inside a rubber hose between diff housing and rubber.,until I get a Diff mount.Been there a year.They make spring pads different thickness to save money buying springs.

Here's the two, side by side:

http://img74.imageshack.us/img74/219...almount0hm.jpg

The one old one on the left,looked like mine.Then I lifted car ,and inserted the bolts wrapped in hose.They haven't moved,even in deep snow.

To just look at the old part, I would have not thought it were bad. I will order a new one. 27 years and 200k miles can do a toll on any rubber part.

It will still function fine...........the problem is the body drops by about 3/4" in the tail due to the old mount. If you are short on funds and don't mind the look, it can probably go another 20 years.

Leveling issues by large have been addressed.. However, in the quest to regain as much of its original glory as possible I've become determined to address other issues one by one.

At lunch today I was at a very long stoplight and put the car into neutral. It was the first time that I noticed a big drop in the rear. Not to say that it was not like that a day ago, but that is the first time I've noticed it.

I now suspect the rear diff mount is due for a change.

Funds no matter how plentiful will always seem short to me.

I will scope out a replacement and address during a future weekend.

Well most do not wish to spend the money on springs, which are almost always one of the largest causes of rear sag. They simply fatigue with age/use, just like valve springs. I mean for the $100 the pair of new springs cost, it is silly not to replace them.

Heck the diff mount is only about $50 retail and can be installed in about 30 minutes. The subframes are only around $75 retail too. So $225 appx in parts for a rebuilt rear is very inexpensive all things considered.

Where are you finding a diff mount for $50, Fastlane is $84?

Edit: Figured it out, AllParts wants $54.