Rear differential fluid change
 

I'm going to be changing out the rear differential fluid and I'm looking for recommendations on type of fluid. Is synthetic a good choice? Anything else to watch for?

I would go with Synthetic since this is an item that does not generally leak and is a relatively high change interval. I went with Synthetic Mobil1 85W90 on both mine and the rear diff is quiet, no noise.
Nothing much to watch for unless the fluid hasn't been changed for 150k miles or has leaked out....just make sure to drain into a clean catch and check for any metal in the fluid.

Undo the top one first, then bottom. Make sure to 'crack' the bolts not tug on them as you can strip them...not something you want. Drain and run through some of the new fluid to semi-flush any leftovers out until it comes out clear. Replace bottom drain plug and fill until it starts to come out of the top then put top back on...done!

How often should the fluid be changed?

Very easy the special wrench is very handy.

I recommend every 100 000km, including gear box.

I use always Mercedes fluids specifications are matched to their hardware.

good luck

I agree. I changed the differential fluid on my 400E at 100,000 and used Mobil 1 synthetic. I never had an issue with the differential over the next 156,000 miles. Maybe the dealer has a better fluid, but it would be hard to imagine you could beat Mobil 1. You will have to get either a 17 mm hex key or hex socket to get the filler plug out.

I think I will change mine, now that you raised the issue.

What is the fill capacity? Is the Mobil fairly easy to find?

Fill until it comes out the top plug. And yes.

Here's an interesting link discussing that the car need not be level for a proper reading of the fluid. I plan to raise only the rear of the car as Loubapache advocates in his post. Does anyone disagree--that it doesn't make much difference whether the car is level to get a correct fill?

http://www.peachparts.com/shopforum/showthread.php?t=29081&highlight=differential+fluid+capacity

Most of the stuff I've read about over filling or the dangers of over filling a gear box or a differential are related to excess foaming of the lubricating oil. If the original design says to fill it on the level using the fill to spill method then I'd stick with that.

Most differentials have a breather pipe on the top that often gets clogged - if this is clogged up and you've over filled the diff then there is a possibility that if the oil expands and / or foams excess pressure builds up - this could cause seals to fail.

My advice is to not think too much about it. Do what the manual says. Don't over fill. You've just put in some lovely new life blood (oil) - you've done the best you can.

If I had a lift, it wouldn't be an issue. But supporting a car on 4 jack stands and getting under it to break loose two large plugs that have probably never been loosened over a 17-year period is something to think about.

No, if you use the correct tool, those plugs will come right out. That said, don't forget to remove the FILL PLUG FIRST! That way, if you can't get it out for some reason, you're not in the situation of no fluid and no way to put any in.

Don't worry about working on sticks!
 

Don't worry about working at height - on axles stands - or on a lift. Do it on the floor:-

1) Get yourself a 14mm allen key with a length of tubing (I used water pipe) or a 14mm allen socket and a T bar (you'll could bust a ratchet)

2) Put the allen key / socket into the fill or drain plug.

3) Crawl back out from under the car and lie on your back - scoot back under head at the back of the car feet going towards the front.

4) Put your feet onto the T bar or pipe and put your weight onto it whilst holding your self on your back bumper!

They'll come loose in the end.

As always be careful and work safe - good sturdy work boots are a must.

Good advice from both of you. I will remove the fill plug first and I will try to do it without jacking up the car. It's been so long since I did my 400E diff. oil that I can't remember if I jacked it up or not. All I know is that I have a 17 mm hex wrench and a 17 mm hex socket that I had to buy to use on the plugs.

Fluid Change
 

Autozone told me the fill capacity was 1 1/7 quart. Fill and spill method works best.

Don't even attempt to break those 2 plugs without a large breaker bar!!! You WILL strip them if you do. I promise.

I called Autozone and all they have in Mobil 1 differential fluid is 75W140. http://www.mobil.com/USA-English/MotorOil/Other_Products/Mobil_1_Fully_Synthetic_Gear_Lube_75W-140LS.aspx

I don't have a specification manual anymore, but I thought it was supposed to be closer to 90 weight oil. Is 75W140 too heavy for a differential?

Stick with the 85W90. IIRC I got mine from Walmart.

That sounds better to me--and probably cheaper.

I should probably add as well that after switching to the Mobil1 Synthetic the 'whirring' noise on the freeway I was getting in the 300TE disappeared. The fluid didn't 'look' too bad either...So...I'm happy with it.

Well, I bought the Mobil 1, jacked up the car and discovered that the 17 mm Allen I used on my 400E was too big for the E420 drain bolt. You were right, Army. I think it looks closer to a 14 mm. Can't figure out why the difference between the two years. The part numbers for the plugs are the same for both years (A 186997 00 32).

The hardest part was getting the bottle high enough to pour into the fill hole. The 2 foot hose extension that you can buy at Autozone is absolutely useless for this (don't waste your money). It leaks all over the place and you still need to get the bottle above the fill hole.

I had to use two bottles and found that I could squeeze enough directly out of two bottles to fill it. You have to jam the bottles up toward the bottom of the body. There's nothing like getting your shirt soaked in Mobil 1 on a Sunday afternoon. At least it wasn't Skydrol.

Oh yes I've been there
 

Yes I had to do exactly that on my W123 - only I think it was on a Tuesday morning... good fun isn't it? Still at least you know it has been done properly.

Take a look under the car once in a while over the next month or so to make sure there are no leaks (particularly from the plugs) - particularly after a long run and the oil has had a chance to get warm

It's nice to know that I'm not the only one. I used Teflon tape on the plugs, but I will check them periodically too. Thanks.

I am going to do this this weekend, any need to use locktite on the plugs? If so what color?

Your Mercedes,Your Pleasure
 

BUT,there's no way In hell I'd risk putting ANY Loctite product on the Differential
Drain Plugs.
(They're "Tapered" Plugs ,Larger towards the "Outside",which is why they can be SOOOOOOO Tight)
[Using Loctite MAY Insure you'll never get them out again!]

"Level" is the correct way to check Differential Fluid.
(The Factory is sorry that you don't have a "Lift",BUT that's your own Problem)
(You really should have taken it to the "Stealer".)

EmeryDC8,

4 Wheels on "Rhino" ramps.
You can pick up a Plastic spring loaded hand Pump that'll fit Quart Bottles.
(Then the Feed Container can be Upright AND below the "Diffy".)
[I use the Picture of the Yamaha pump 'cause it's what's in the Garage]

Are the Rhino Ramps short enough to slide in front of the rear wheels too?

I Just Love it ,when I 'Ave to eat crow.
 

Rhino Ramps Height specifications in Below Picture.


'Silly Me, I use the 3K Lbs Floor Jack on the Rear Jacking Pads (In front of Rear Wheels) and then Hand Place the Ramps under the Rear Wheels.[Facing Backwards]
(I Gotta be creative,since I'm "Lift Challenged")

And My "Murphy" consultant tells me She'll get Two Weeks all expenses paid in Paris this Spring,If:
"You'll only just try BACKING all four wheels at once onto the Ramps".
(Nod,Nod Wink,Wink)

(For Our Newer,Less Suicidal, Members: NEVER,AT HOME or ABROAD, try for the "Four at Once" "Ramp Lift" METHOD.'TOO MUCH RISK OF CALAMITY to Chassis.)

No need for loctite the plugs, they are conical (much care is necessary when you tighten them back, they may break everythings)

I have my diff out of the 87 TD and will be reinstalling tomorrow. I guess I'll pick up synthetic fluid since it only needs 1.2 qts. I have attached a hose to the container and squeezed into fill hole on other projects. Having the diff out on the bench makes this an easy service.

(I am replacing diff bushings and SLS accumulators).

There are 2 options. One is to buy a suction gun at $12-20. The other is to use a section of hose (3/8?) firmly placed onto the cone shaped cap, or drill a hole in a cap and have the hose tight fit inside.

Use of the suction gun is self explanatory.

The hose method on the bottle allows you to squeeze the fluid UP into the fill port. This has worked like a charm for me for many years. It you are making a mess then your procedure needs to be amended.

Best of luck.

RE differential oil change 2007 E350 (base).

Save yourself headaches and order a Plews model 55001 1-Qt. Lubrimatic Fluid Pump.

US$6.10 on Amazon at this writing.

Using the Plews pump I spilled maybe ten drops of oil on the floor.

Screws onto top of Mobil 1 gear oil bottles.

The Mobil 1 gear oil bottles have a gauge on the side of the bottle.

Do the math to pump in ~1.17 liters of oil. If the car is flat, the oil will start to run out of the fill hole when you reach ~1.2 liters of oil.

Remember, always take the fill plug off first (in case you can't get the drain plug out, you can halt the project).