I have searched but cannot find a DIY for changing my diff fluid. Is it because it is so easy nobody has bothered, or am I searching with the wrong terms or in the wrong place (I only searched C32 forum; does another chassis share our diff?)? If none exists, does anyone know if the diff has a drain plug, or do I have to remove the cover to drain? Thanx!

try the r170 forum benzworld many threads there. mine has a drain plug on the bottom and a fill plug on the top. 14 mm hex socket needed. takes mobil 1 synthetic 75/90 wt. i needed 44 ozs in mine. should be done every 40 k or so

Rule #1 is always remove the fill plug BEFORE the drain plug. A hand pump that screws onto the oil bottle helps too. We don't have LSDs, so choice of oil is pretty wide open.

That is exactly what I needed to know. Thanx for the info. Gotta go buy some metric hex sockets...

I was aware of this Rule, but it certainly bears reminding everyone who may read this thread. Without an LSD and thus no need for a friction modifier, choice of lubricant certainly opens up. I will lean toward Mobil 1 simply because the Base Exchange has a full selection, though I've had good luck with Royal Purple and Amsoil in the past. Thanx!

harbor freight has a set of hex and square sockets for about 15$. i use the mobil 1 simply because i have mobil 1 in all the other oil holes
advance oil has the hand pump that fits on the oil bottles. a must have as you cant tip the bottle into the fill hole. about 8$

Digging up this old thread because I can't seem to find an answer anywhere... I just had my transmission fluid completely flushed and replaced with Fuchs 4134 (the newest fluid) at my local indie (Silver Star Motors of Vienna). My car had 42,000 miles at the time of the service.

At the time, I really didn't give any thought to the differential fluid. Threads covering changing the differential fluid and how often you should change the fluid are sparse in this forum.

Page 388 of the owner's manual in the "Fluids" section references a "Rear Axle" fluid. Is it safe to assume this is the differential fluid? It states that the replacement for the C55 is 1.5 US qt. of Hypoid gear oil SAE 85 w 90.

Also, how often is this fluid supposed to be changed? I am going to be kicking myself if its every 40,000 miles as I would have just had my indie do the change while it was in the shop for the transmission flush.

Yes, Axle fluid is the same as diff fluid.

A lot of modern cars have a "lifetime" fluid that theoretically does not need to be replaced. I don't trust that BS and would do it every 35-40k miles depending on driving style (My old M3 manual recommended it at 50k and that had an LSD).

Super easy to do.

...as DIY or for a mechanic? Do you know how to replace it? I was always under the impression that changing the differential fluid required pulling open the differential itself?

Just be prepared for the real bad smell!

It's not difficult if you have a decent pump to get the new oil in, one that fits on top of the oil bottle. I didn't and it still took me all of a half hour to do.

Just remember to remove the fill plug first in case you can't get it off. It'll be a bit late to find that out after you've removed the drain plug.

It's really easy mrobinso. I am no mechanic (thank God!) and I have done it a few times on my trucks. Here is a quick DIY:

1. Jack up car in back and place on jackstands. I use a set of Rhino ramps with my Tacoma and it saves the jacking. http://www.amazon.com/Blitz-Rhino-Ra...8387725&sr=8-1
2. Find the "pumpkin" in the rear axle. It's where the diff and drain/fill bolts are.
3. If there is a separate dedicated fill bolt, remove that.
4. Remove diff drain bolt. Usually takes just a 1/2 inch or 3/8 inch drive. From my Ranger and Tacoma, they don't need any sockets, just the half inch drive. Could be different for the Merc.
5. Suck out the old fluid. I use a Mityvac fluid exvacator, but I have heard cheaper pumps available at Autozone also work successfully.
   http://www.amazon.com/Mityvac-7400-L...sr=8-1-catcorr
6. Re-fill diff with recommended fluid. I have seen both ways - re-fill using same bolt or re-fill using a separate, dedicated bolt at a higher point on the pumpkin. I have never had to use a pump to re-fill, the diff fluid bottle comes with a funnel that usually suffices.
7. Close up, drive a few minutes. If you are really cautious, re-jack car and check level. But as long as you got recommended or close to recommended amount of fluid back in there, you should be fine.

Are there any signs/issues that would signal someone to know its time to change the rear diff fluid? With the comment I saw about "lifetime" fluid, how could someone verify that is what they have?

xxaarraa, thanks for the great post! If it is really as easy as this for the C55, I already have all the tools I need to do it myself (including the pump). I just need the fluid. Have you done this on your C55 yet? Has anyone else or can anyone attest the similarities to xxaarraa's above listed steps when performing this DIY on the C55? Thanks again. Now to find a place I can purchase the replacement fluid...

quality 85W90 gear oil. For the rear diff.
Mobil works good. Fuchs titan etc. 1.5qts capacity
The maintenance manual has the frequency of changing schedule. But if yours is an 06 it is due.

I always make sure I open the filler bolt first, just in case you strip it out after the fluid is emptied. then your hosed!

Well, I didnt see this post.. but its great advice.

I have not done this yet on the C55, I only have 30k miles and plan to wait till 40k. I would go to autozone or NAPA and pick up Mobil 1 diff fluid / gear oil in the recommended weight (per manual. 75-90?). You could even go straight to the dealer and get what they recommend, may be a few dollars more than NAPA, but more certainty on compatibility.

uses 85W90

Yes the owner's manual states the above SAE 85 w 90. Autohausaz has 1 liter of the MB brand fluid for $28 a liter (obviously I would need to buy two of these). This was the best deal I found just from Googling around. Any input onto how fair this price is?

Changed mine yesterday...you'll need a 14mm hex and the hand pump. Only takes about twenty minutes and my car
really seemed to benefit from it. I used 75w90 mobil1. Plenty of people have used it with no problems.

Can anyone provide insight here? The MB Spec Differential oil (85w90) is $27 a liter at www.autohausaz.com while the Silkolene brand gear oil (85w90) is $8.50 a liter at www.amazon.com.

Call me naive but, aren't they the same thing?

http://www.amazon.com/Silkolene-Medi.../dp/B00330M55C

http://www.carpartsdiscount.com/auto...3681&3671=1002

Can anyone provide some input here? Sorry if this is a dumb question I just haven't been able to find an answer elsewhere. If the fluids are the same, what gives? Is the MB stamp really worth the additional $22 odd dollars?

The mobil 1 works great and protects just as well and is synthetic while the others are not

I went ahead and ordered 2 liters MB Brand/Spec 85w-90 hypoid gear oil, about $60 from autohausaz.com. Go read this thread and it will the living tards out of you and make you want to use the MB spec oil.

https://mbworld.org/forums/e-class-w...il-change.html

I'm Not using 75w 140! I'm using 75w 90! Research it! The only differences are that it's synthetic (+) and that it isn't as thick in cold weather (+). Same protection capabilities (+). 3 positives no negatives. The thread you're referring to it's discussing 140 weight not 90 weight!