My Differential FELL OUT WHILE DRIVING!! W126
 

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?

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?

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

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

:eek: 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.

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...

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.

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?

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

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.

Glad you (+general public) are OKay
 

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

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

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

Sorry for being such a noob, but is the W126 rear end similar to my W124?

I just got my car back from the mechanic. Wow, I am amazed. Everything is in working order (except I now have an ABS light on), and the total cost was.... Drum roll.... $64.50. That's from a mechanic who charges $95 an hour!!

The only thing that is amiss (other than some metal) is now I have my ABS light stuck on, so I am assuming that perhaps a wheel speed sensor got broken, or the wire pulled out.

Can anyone suggest a place to look? I didn't see any sensors near the rear wheels. Where are they?


Thanks!

The sensor is on the passenger side of the differential, behind the drive shaft flange.

Rob

Thanks!! I'll go check it out. Probably just yanked the wire off, or broke it.

Well, I was right. Busted the thing right off. Mechanics didn't notice it because the wire end managed to tuck itself away inside the control arm!

From the looks of it, my pinion seal didn't survive. Somehow I knew $64.50 wasn't the end of it...

Can you tell from that picture of the wire if I lost my plug end, or busted the sensor? I can't get up under there enough without ramps or a lift.

All differentials bolt to the frame somehow...

Looks like the cover and bottom bolts got a good shave.
http://www.peachparts.com/shopforum/...6&d=1286313112

Next time the cover is opened up. You most likely not be able to reuse it. Be sure to check for leaks in the future in that area.


http://www.peachparts.com/shopforum/...8&d=1286314995

The sensor is busted. You'll need to replace it.


.

Thanks for the info, much appreciated. Wow, that sensor is $200. I am going to have to see if I can scrounge one at a junkyard before I plunk down. Hate to be cheap, but that's a pricey sensor.

panzer, why don't you discuss the situation with the indy who worked on your car. Either the sensor was damaged when the differential broke loose, or the indy damaged it when he was working on your car. Regardless, a knowledgeable and thorough indy would have seen the sensor was damaged, and definitely seen that the ABS light was illuminated. Why would he return your car to you with an obvious problem?

I see your point, but these guys are definitely knowledgeable. They've been working on Mercedes, BMW, Jaguar, Rolls, and Bentley for well over 25 years. The sensor was certainly busted when the differential fell; the plug doesn't have enough slack to have survived the differential falling to the ground. Plus, I got under the car after it was towed back, and I didn't see the wire there at all. When I started searching for it, I discovered that the wire had tucked itself completely out of sight inside the lower control arm.

As to them not noticing the ABS light, all I can say is who knows. For one thing, the light doesn't come on until you've driven a short distance, and also the warning lights on a W126 cluster are not the easiest to see. If you aren't either quite tall, or have the wheel all the way in, the bottom row of lights likes to hide behind the wheel. Anyone who has a W126 can tell you that they've driven with the brights on for some time because the indicator is nearly invisible.

At any rate, I can't fault them for the sensor. It was toast before they looked at the car. Besides, how many mechanics do you know that would only charge $64.50 for putting your whole rear end back on? Most mechanics would have told me that I needed new axles, flex discs, or some other way to bilk me. Anyhow, the sensor is not that big a deal. I can scrounge one at a boneyard. It's the leaky pinion seal that really sucks, and is likely to be expensive. I could do it myself if I had a lift, but I ain't screwing around with the driveshaft lying on my back with the car on ramps.

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.