I was thinking a fluid change can't hurt, can anyone give advice, 1986 420SEL:

How often is needed?
Easy to drain?
type of fluid?
Amount required?

I don't know the fluid and quantity specs for your car, but remember to remove the fill plug before the drain plug. Also, its a good idea to remove the vent plug and clean it. I always use the 85W gear oil that comes in 1 liter plastic bottles. You'll probably need a 14mm allen wrench.

------------------
'82 300D Turbo 219k miles

Checked the rear differential oil today. Level seemed to be down a little - with little finger in the hole to first joint oil just touching the tip. The oil in the differential was very red (almost looked like ATF, but smelled like 90W), not golden brown like most 90W I've seen.

Is this MB specific gear oil? Can I use regular old 90W?

Should I just top off or completely drain and refill? I have no idea whne the last time the differential oil was changed. The fill plug came out easily, I'm sure the drain plug will too.

__________________
Mike Tangas
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72

'02 CLK320 Cabriolet - wifey's mid-life crisis

2012 VW Jetta Sportwagon TDI...at least its a diesel

Non illegitemae carborundum.

I have seen some that will look red on your finger. I don't think it's critical exactly what Hypoid oil you use as long as it's Hypoid gear oil and not something else.

It's plenty simple and easy enough to change it. Since you don't know how long it's been in there it wouldn't hurt.

Plain old 85W90 or 90W will work fine. I got a five gallon bucket of stuff many years ago, when my 240D was young. I've changed it about every 100,000 miles and have had zero problems with the rear axle or suspension in any way.

The only reason you would have to be picky about the lubricant, is if it is a limited slip.

To answer the original post in this thread, I don't know the exact quantity, but it's not much. The main thing is to just drain it, and fill it back up 'til it runs over. The suggestion to remove the fill plug before the drain plug, is a very good statement of wisdom.

Good luck,

I think I'll just do an oil change on the rear diff, just because I don't know when it was last done. The oil I did see on my finger was clear, I just don't know what it looks like at the bottom of the housing (I checked the oil after the car had been sitting all night). Judging by the size of the housing, I don't imagine it will take much more than 1 quart of gear oil.

Should I get the rear diff to operating temp before draining, to float out any debris?

__________________
Mike Tangas
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72

'02 CLK320 Cabriolet - wifey's mid-life crisis

2012 VW Jetta Sportwagon TDI...at least its a diesel

Non illegitemae carborundum.

Mike,

Although a gear box does not produce contaminants like the combustion process in the engine, if the lubricant is churned up and warm, you have a much better chance of getting out any slivers which may be in the case. I try to do the same thing with differentials and manual transmissions that I do with engines. It may be a waste of time, but it can't hurt anything.

Good luck,

I did mine a while back. It was for maintenance purpose only, since I did not know when the last oil change was. I did use hypoid gear oil (one full bottle). I do remember that it was a bi*** to get both plugs out. I got the fill plug out first, then the drain plug and lastly the vent which is located in the top rear of the differential.
Good luck!

__________________
J.H.
'86 300E

Metal particles are the crud I was referring to, I'm hoping the bottom level fluid is as clear as the upper. I also plan on straining the gear oil through cheese cloth, just to see what is in there. Can't be too careful on a nearly 30 year old differential (or whole car for that matter).

I do remember on a Ford P/U I had, the syncros went south, and when I popped the top cover on that New Process 435, the gear oil looked like liquid gold from the brass/bronze syncro material emulsified in the gear oil, but that is another story.

__________________
Mike Tangas
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72

'02 CLK320 Cabriolet - wifey's mid-life crisis

2012 VW Jetta Sportwagon TDI...at least its a diesel

Non illegitemae carborundum.

What would really be ideal here, would be a magnetic drain plug to capture the metal slivers.

In the sixties, there were many Fords with magnetic drain plugs in the rear axles from the factory. I used to get them at the wrecking yard and use them in every transmission and gear box that I had. It was simple because all cars were the same size pipe thread drain plug.

In the case of our MB's I would guess that the only way you would have a magnetic drain plug, would be to make one.

My $0.02,

For your consideration, I use synthetic in my diffs (Red Line 75W90) and it's worked perfectly. Since synthetic has superior properties to any dino oils, I run it in both cars (500E with some limited slip, 300TE with open diff) and have had zero problems in 130k miles (100k wagon, 30k 500E)and counting!!

__________________
"If God had meant for us to walk, why did he give us feet that fit car pedals?" Sir Sterling Moss

Michael
2014 E63S Estate
2006 SLK55
1995 E500
1986 Porsche 944 turbo

I read the posts for changing the rear end fluid and went to the dealer to buy the MB fluid. There are numerous references to using the MB fluid, not just 90 weight. The Parts Counter guy told me that they all just use 90 weight and don't even have the MB fluid. He didn't ask if I have limited slip (and I do) but it didn't seem to matter.

What is the issue with the special fluid for the limited slip differential?

Steve
'85 500SL (Euro)

Most of the hypoid gear oils you buy by the quart are okay for limited slip. You need to read on the container. If it does not say so, go get some that does.

At the auto supply they usually have it by the quart, and most all I've read the label on, were for limited slip.

You can get an additive for limited slip at your chevy dealer if you can't find any that is designated for limited slip.

Good luck,

At the parts house last evening, I was 90w shopping. Saw plenty of dino, synthetic and blends. Some were clearly marked "hypoid" others clearly "hypoid, suitable for limited slip". In the course of my reading, I encountered a number of gera oils that were parafin based as well. In light of my disdain for parafin based oils, I chose a Valvolin all petrolium based oil.

__________________
Mike Tangas
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72

'02 CLK320 Cabriolet - wifey's mid-life crisis

2012 VW Jetta Sportwagon TDI...at least its a diesel

Non illegitemae carborundum.

The rear diff oil is now changed. I collected the old oil in a opaque milk jug, and it still looks very red. Have no explanation for it, but now that I can get my nose in it, the oil has that burnt smell to it. Probably due to age and the heat transfer from the muffler/tailpipes in the immediate area.

Experience is a great teacher. Drove into town to get a cup of coffee and warm the gear oil (14 miles round trip). Got home and put her up on ramps, pulled the fill plug and positioned the jug and funnel (w/cheesecloth as a filter). Once I pulled the drain plug, the flow of warm 90W was faster than the rate of drainage through the cheesecloth and funnel. Next time, I'll keep the fill plug in and crack it occasionally to meter the out flow and eliminate the cheesecloth. BTW: no particulate matter in the cheesecloth.

__________________
Mike Tangas
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72

'02 CLK320 Cabriolet - wifey's mid-life crisis

2012 VW Jetta Sportwagon TDI...at least its a diesel

Non illegitemae carborundum.