How to change diff oil?
 

Hi All,
Please explain me how to drain the differential oil, and how to fill up. Diff is whining a lot, and want to replace standard lube with Valvoline HP Gear Oil GL-5 85W-140 (No Redline/Swepco here...)

Thanks!

For starters, remove the FILL plug first, just to make sure you can do it! It's harder to remove than the drain plug, and I'd hate to have someone drain the lubricant and have no way of refilling it! Use an antisieze compound on the plugs so the job is easier next time.

Do it hot.... it flows better and you can drain more of the crud out of there faster.

I find if I jack the car up there's enough room to use the regular bottle the lubricant came in for filling.

Auto part stores sell an "extension hose" to fill diff oil.
 

It only cost $3-4. It will make the refilling a lot easier. Room to manuever the bottle is VERY limited up there.
There is also a vent located high behind the differential (at least in my car), it looks like a bolt with a "top." Remove it, if you can, clean the screen and re-install.

Gear Oil
 

An 85W-140 sounds pretty thick to me...

Are you sure this is what is called for for your MB? I used the Synthetic Valvolene product in a lighter weight and my shop guy said he felt it was good to go for the life of the car. Also saw a slight mpg increase.

I've been wrong before. But, check the spec? :cool:

Re: How to change diff oil?
 

Why that heavy stuff? It's probably better to stick with the MB recommended weight. I use Mobil1 in all my cars and find it has been excellent.

The Mobil 1 differential oil product is a good recommendation. It is a synthetic oil and for me it has made the differential whine significantly less. I have also noticed the synthetic has a cleaning effect on the inside of the differential - had it apart to change axles.

A little more expensive than dino - but I think its a superior product.

Ken300D

Re: Re: How to change diff oil?
 

Thanks for the help, guys.
Did a search on this board, and 85W-140 is recommended for whining diffs in a lot of posts on this board:confused: :confused:

85-140 is way to thick and not what is recommended by MB. First try just changing your old oil and see what happens. Your diff could be whining because the oil is old, or you may not even have enough in there. I changed the diff oil in my '84 300D about 7 months ago and I swear it was the original stuff in there. There wasn't enough in there, and the stuff that did come out was unbelievably dirty and foul smelling. Just putting in new oil made differential whine go away almost completely.

Just try changing it first.

GregS
'84 300D
'90 300CE

You might also want to check your diff gaskette seal for leakage.

What stink!
 

I changed my diff fluid and I never smelled such foul odors. Do not spill it in the garage! 100,000 miles and 15 years old? Who knows. The Prev owner had no records and I don't know if it was ever done.

I wondered if it is done on the flat floor. I jacked up the rear and filled the diff then set it down, let it drip and then jacked it back up and put in the plug. I think that works. I used regular gear oil but added some additive for the limited slip diff.

Seems to be great 15,000 miles later with no noises or anything.

What's the diff?
 

I certainly agree with a couple of the latest postings. The concept that if 10W-30 oil is Good!, then 5W-50 is (somehow?) Better! and 0W-75 would have to be Best! has , I hope , already been de-bunked more than a few times...

My reading has led me to believe that a viscosity spread from 85W-140 may be needed (and spec'ed) for a mucho! higher load rated rear end, but is not required or even desirable in a car/light truck/SUV application.

If the whine goes away after a fluid change with that which is recommended you should be good-to-go for quite a while. If the sound remains, perhaps further investigation might discover the cause before it leaves you stranded :eek:
or, worse yet, needing a new read end?:confused: :(

Just a thought!:cool:

Also, in my experience in taking off the differential back cover on just one car, a 1982 300D, there is no gasket seal there. Either it was omitted in a previous maintenance action, or Mercedes doesn't use sealing gaskets for that vintage differential.

Recommended sealing method is with RTV Blue sealant. Don't put it on so thick that it squeezes into the insides of the differential - and let it cure overnight before refilling with oil.

But you won't be doing this just to change oil.

Ken300D

Viscosity modifiers
 

I understand the downside to multivicosity oils is that modifiers displace the lubricant and have no lubricating properties. You can have up to 30% modifiers by volume in an oil. These modifiers do not lubricate. They are there to thicken the oil. The base mineral oil does the lubrication.

Another downside is that engine oils with a high amount of modifiers tend to leave more deposits than those with low amounts of modifiers.

It's for those two reasons I use 10W30 instead of 10W40 in my engines.

Therein lies the tradeoff.

Straight weights?
 

Why not run straight 30 in the summer and straight 40 in the winter?

Uh....?
 

Wouldn't that be the other way around?

p.s. This may apply to both the 30 vs. 40 post & the concept that "more modifiers = more deposits"? I certainly agree with the s-t-r-e-t-c-h argument (Ooops! I meant "position")

p.p.s. I guess if you get the stuff outta' there on a timely basis there won't be any real deposits to worry about:cool: