All,

I figured I'd share my "recent" issues with my 2017 base model (70K miles). A while back, not sure when, I started hearing what sounded like a failing rear wheel bearing. It was very faint and of course my wife had noticed it (her car) .

It eventually got to the point that things didn't make total sense to me and it was getting quite loud, a whining noise, not a grinding or rumbling. I've only had one wheel bearing failure (rear) in a car in the past, while on a cross country road trip, go figure. It went from nothing to loud grinding/grumbling noise while going in a straight line, turning, etc. The noise got louder with vehicle speed. Anyhow this GLC was not exhibiting the same symptoms. It started only making the noise while turning, left or right, didn't matter. Still thinking it was a wheel bearing I decided to purchase some to determine which side. To make a long store short, the left and right components I tested all sounded the same. Soooo, then I decided to see what the differential sounded like. The differential housing did make a different sound when turning than when going in a straight line.

I eventually got fed up and took it to an independent shop (I refuse to use the dealer unless I have to $$$) to see what their opinion was. Essentially they didn't tell me anything that I didn't know other than confirming my suspicion that something was wrong with the differential. I changed the oil and ran it for several hundred miles but no luck. At this point I was convinced the diff was rapidly going bad.

After researching rebuilding that was a no go, buying a new (remanufactured) from Mercedes...$$$ yikes, I decided to see if I could get a used unit.

After MUCH research and I determined that I found a decent unit on Ebay from a car with the proper diff in it. I spent a lot of time comparing VINs to make sure it would be correct.

Pulled the trigger and bought one for $600 delivered for a 40K mile unit. Showed up nice, pulled the cover off and everything looked in order visually. Cleaned it up internally, installed new carrier (side seals) because it was easy and sealed it back up.

I spent about 10-12hrs over two days in 90F+ temps in my garage removing the old unit and installing the used one. uugghh The whole time in the back of my mind I kept asking "what if it isn't the diff" or "what if the used diff is bad". I'm not new to wrenching as I've been working on our cars forever so this wasn't too bad but there were some challenging areas. I did have a big oil spill and took a bath in the horribly stinky differential oil. YUCK.

Buttoned it back up and took it out for its first trip and YES.......ITS FIXED.....SILENCE. What a relief, saved us a ton of money (for now). It is a used unit and no telling how long it will last but hopefully it will give us another year or so before we move on to another vehicle.

Here is a picture dump if you are curious or maybe it will help someone.

I plan to take the original unit a part but I won't do that until I get more miles on this used one. I want to get the carrier bearings out as it will probably obvious that one of them is/has failed.

 

Lotta work, nice result.

Nice tranny jack. What make?
Do you feel comfortable with wired Chassis Ears, that you can secure the wires and drive for, say, a few days safely?

 

That is a 25 year old Harbor Freight(?) jack from back when I was modding one of my Corvettes. It is way overkill for that small diff. The strap and ratchet are way too big but it did the job along with some pieces of wood to get the angles right.

The wired chassis ears are somewhat of a pain, especially keeping the wiring away from moving or hot parts. I cheaped out as all I needed to do to recreate the symptom was drive around the neighborhood so the velcro straps it comes with, tie wraps and lots of tape did the job. My setup definitely would have worked at high speed. If I wanted or needed to drive it for days I would have considered the wireless.

Rick

 

Good job! Are you the original owner, is the load heavy in the vehicle all the time or you only have a driver and a passenger, lots of cargo? lots of people at the back, do you tow, when was the rear differential fluid changed on the old one? If you haven't already, might consider front differential fluid change as well, for some reason MB doesn't have an official interval for that one,

That sense of accomplishment when you bolted it back up and hear no more weird noises is such an awesome experience!

 

Any diagnosis on the failed unit? I'm guessing one of its bearings? Could be an easy fix to have available in case the replacement diff craps out.

 

Just had the front differential start going out on our 2016 with 77K. Never replaced the diff fluid because, to be honest, didn't ever come up on my radar due to MB not having a service interval on it nor anyone suggesting we do a fluid change (now we know it's probably a good thing to do every 50k or so). Wife drives the car like a cream puff and never towed.

Small town MB dealer quoted $4400 (guessing the higher-priced dealer near us would have been about $5,000). Independent German specialist garage quoted $3900. We paid the $3900 and she runs like a top again. I envy your enthusiasm and knowledge to get this done yourself.

 

I honestly don't understand why MB don't have service intervals for front differentials either, I mean it does all the heavy lifting, holding the engine, assisting with the turning maneuvers, the poor diff is tiny with a small amount of fluid and gets stressed all the time.

 

Yes, original ower. No heavy loading, all normal daily type driving, wife going to work etc. No tow hitch. Maybe has two people in the back once a year.

Fluid was changed AFTER the noise at say 69K miles (yes, I think 60 is what Merc suggests). It is a base model with RWD.

Rick

 

I haven't taken the original a part yet just in case. I probably will in several hundred miles on the new unit. Hopefully I can get it disassembled relatively easily. It appears the carrier bearings are held in with a huge snap-ring (see pick). My gut tells me one of them is bad. It should be obvious once I get one out.

 

That is how much you paid for a new front diff? That is cheaper than I would have expected.

I love wrenching and HATE paying people for something I can do. That being said, Merc doesn't make it easy for the do-it-yourself owners AND there are much fewer YouTube videos that can help since most owners don't work on their own cars. You should have seen the guy at the parts counter when I was buying new seals and he asked for the VIN. I said, well, the VIN for the "donor" car at the salvage yard is.....his jaw dropped. LOL

I installed a new differential (better performance gear ratio) in one of my Vettes (2000 5th generation) many years ago on purpose, not because I had too. 20 something years later this old body hurts a little more crawling around on the ground. Here are some pics showing the rear cradle as well as the differential and transmission still mated together along with the torque tube (driveshaft inside). Yes, the transmission is in the back for weight distribution purposes.

 

I have a '95 Jeep YJ with Dana 30 (front) and Dana 35 (rear) differentials -- 75K miles and both gear boxes have been used and abused with towing heavy loads and pushing a snowplow. I had to replace the AX15 5 speed transmission about 9 years ago (reverse gear failed), and the NP231J transfer case 3 years ago (leaking seals), and I installed a new clutch (for the 3rd time) last year. But both original Danas are still hauling the load. Seems as if German engineering has set back differential design and reliability by at least 30 years.

 

RWD, nice! At least you only have to deal with a rear diff for the lifetime of the vehicle. Thanks for the data point.