My Differential FELL OUT WHILE DRIVING!! W126 - PeachParts Mercedes-Benz Forum

tinypanzer · #1 10-04-2010, 02:14 PM

Not wanting to be one to disappear from the forum for a couple of weeks, only to re-appear with some sort of lame observation, I thought I would delight you with the story of how I almost died last night.

On the way home from work, I slowed to take a right hand turn. As I accelerated out of the turn, I heard a loud BANG from the rear end. The car dropped a few inches and then ground (literally!) to a halt.

After getting out and inspecting the situation, I had discovered that my rear differential had COME UNBOLTED FROM THE FRAME and was now dragging on the ground!!!!

What makes this so friggin' scary is that for some reason I decided NOT to take the interstate home at the last second. I was about to get on I-10, when for some inexplicable reason I decided to take the local roads home. It really was a last second decision, almost like fate intervening on my behalf. If this thing had let loose at 70+ MPH, I'm not sure I would be sitting here today.

Check out the picture. Gotta be worth at least 1000 words, if not $1000. Has anybody ever heard of this happening? I know one thing's for sure, I will be inspecting every nut and bolt under there religiously from now on.

So, I had to sit in the middle of the road for about 30 minutes with a nice Deputy Sheriff before the tow truck came. Then I got it towed to my indie. I put in a call to MB to "See what they have to say about all this". I won't hold my breath.

Thoughts?

Rahulio1989300E · #2 10-04-2010, 03:27 PM

Good Lord...

I think that if this happened on the highway, it may have caused you to spin out or grind to a halt very quickly, but I think it would be worse for anyone driving right behind you. They would be faced with a 100lbs chunk of metal to slam into or dodge if they had the wits and attention at the time...

Scary! Rust issues?

tinypanzer · #3 10-04-2010, 03:33 PM

Not a SPECK of rust on this car anywhere. The bolts simply fell out.

S-Class Guru · #4 10-04-2010, 06:01 PM

The service manual says to use these 4 bolts only once, as they are self-locking and only torque to 20 ft/lbs.
I'm certain I've had mine out at least 3 times, maybe more, and never replaced them. Wonder if I locktited them????
Think I'll crawl under there tonite and just check them out.

Along similar lines, a couple weeks ago I was working on the driveshaft, and needed to remove the rear tranny mount - it came out in two pieces! The rubber cubes had totally separated from the lower metal, and were only being held up by the "V" shape of the lower metal portion. But that little vibration I had noticed for awhile went away.

Then there's the one about putting the idler arm bolt in upside down, cause it won't clear the exhaust pipe when trying to install from the top on a 300SE. It has a self locking nut holding it on, and lot's of guys do it, but I just couldn't.

We kinda take things for granted, as well as these old S-Class tanks hold up. But in the long run, they are just machines, prone to loosening and fatigue just like a Ford. Take heart in knowing, though, if you had to take a rollover trip down the freeway at 70 mPH, you have a very strong car to do it in.

DG

tbomachines · #5 10-04-2010, 07:28 PM

Holy crap. This is one good reason to crawl under the car and make sure everything is tight and in good working condition. You're lucky you made it to a stop safely, plus the diff should be pretty easy to grab from a junkyard if you keep your eyes open.

Fulcrum525 · #6 10-04-2010, 07:46 PM

That's a new one....has there been any work done on the rear end recently?

tinypanzer · #7 10-04-2010, 08:16 PM

Quote:

Originally Posted by Fulcrum525

That's a new one....has there been any work done on the rear end recently?

Not since I've owned the car, about 2.5 years. While the back end hasn't seen any work that I know of, I and several mechanics have inspected the suspension. How I missed this, or how long it has been going on, I just don't know.

This whole experience has been very informative, and although I already had a healthy respect for inspection and entropy, I have really had my eyes opened by this. The fact that I made a last minute choice not to get on the interstate has interesting philosophical implications as well.

As an engineer and technician, I comprehend well what happened, but in many ways it has yet to really sink in. I cheated, at a minimum; a horrible accident at high speed. Possibly more...

shawnh · #8 10-04-2010, 08:33 PM

Did someone take the "cover" to the driveshaft off at some point in time? It seems to me that the driveshaft being held up would have kept the differential from falling very far. I just removed a differential today at a wrecking yard(to get at the axles, since i did not have the 12 point star bit to remove the flanges on the "upgrade" axles). It took a lot of work to get that differential to the ground. They added a "hanger" on the differential cover on the later 126s, that gives it a redundant support. Maybe those will fit on the older differential as well.

Glad to hear fate/God intervened in your situation.

tinypanzer · #9 10-04-2010, 09:03 PM

Not sure, I don't think mine has a cover. It's a '90 so maybe that didn't exist on a 300SE. Was the car you picked a V8?

tinypanzer · #10 10-11-2010, 04:10 PM

Quote:

Originally Posted by shawnh

Did someone take the "cover" to the driveshaft off at some point in time? It seems to me that the driveshaft being held up would have kept the differential from falling very far. I just removed a differential today at a wrecking yard(to get at the axles, since i did not have the 12 point star bit to remove the flanges on the "upgrade" axles). It took a lot of work to get that differential to the ground. They added a "hanger" on the differential cover on the later 126s, that gives it a redundant support. Maybe those will fit on the older differential as well.

Glad to hear fate/God intervened in your situation.

To answer your question, no the cover was there all along. It wasn't strong enough to keep the diff from hitting the ground though, it bent.

Got a new sensor Saturday and PnP. Bought about $85 worth of stuff, didn't even get charged for the sensor. What a PAIN to put it in though, you have to remove the back seat! I pulled it off a '91 300SE that had 354,000 miles on the clock! Oddly, the wood trim on the center console was PERFECT and a really nice piece of zebrano. I scored that and all the switches for $10, and I am a really happy camper at the moment.

DieselPaul · #11 10-04-2010, 09:08 PM

That's new to me, good to hear you're okay.

macdrone · #12 10-04-2010, 11:52 PM

Bushing being old and have plenty of play could have loosened those after time. My 400E has some rust but my bushings are shrunk so i check for play alot in the bolts.

compress ignite · #13 10-05-2010, 03:18 AM

'Just one more set of bolts to add to the Must be Used only once...
AND MAKE SURE the New Ones are Loctited!

Stretch · #14 10-05-2010, 03:54 AM

Wow - I'll be checking my bolts - thanks for the warning.

S-Class Guru · #15 10-05-2010, 10:10 AM

The center cover is a good point. Yes the '90 300Se has one; it's a 1/4" aluminum plate about 2 feet long, and covers the center bearing area above the exhaust.
Of course, the force and leverage of a diff coming loose while moving may have just ripped the rear flex disc apart. So, check for driveshaft damage also.

DG