Diff. Sensitive to Fluid Level?
 

So my rear end was making a very loud clicking noise, kind of sounded like something was binding up. It would only start to do it after I drove the car for a while, like something needed to heat up before the noise would start. I couldn't figure out what it was, I checked the wheel bearings and the cv joints and they all seemed good. So I pulled the fill plug out of the differential to check the fluid. Nothing started running out when I pulled the plug so I put some more oil in it. I'm not sure how much I put in but it couldn't have been any more than 4 oz., if that. Now the sound totally went away! Are the diffs VERY sensitive to the fluid level? It seems to me they should be able to operate just fine if they are a few ounces low on fluid, but maybe I'm wrong?

Why would you figure that?

It doesn't have an oil pump to send pressurized oil to the gears..........relies on strictly the splash from the ring gear passing through the sump. Four ounces represents approx. 15% of the fluid capacity, but may represent 30% of the available fluid that can splash (the remainder sits below the ring gear).

Well, this is my first Mercedes but I have worked on a lot of 80's trucks before that have been maybe 50% low on gear oil and have run fine for thousands of miles like that. I'm not saying it's good for it I just figured they would have allowed for a little more "tolerance" in the gear oil level.

What's your definition of "run fine"?

If the diff runs for 10K and develops noise due to excessive wear on the splines............is that "running fine"?

In reality, you have no idea if they "ran fine" unless you had sufficient data that proves they can go 100K on 1/2 the oil quantity.

And, if you had that data...........why wouldn't the manufacturer have produced the vehicle to operate with 1/2 the oil quantity?

Boy, some people in this forum sure are sensitive. Or just **********, I can't tell which...
inappropriate language

Some of us are sensitive but I don't think that is the case in this situation.

You might find that synthetic oils make the diff run even quieter...

Seems that BC's comments are valid.

Kinda like saying I smoke Camel-straights for 10 years and I don't see any problems. Maybe, maybe not - seems best to follow the procedures the good Germans recommend.

Calling someone an *-hole because you make a nonsensical statement and he calls you on it.

What clever name will you give me?

Hey Ol'Smokey, :)

When I first read the title of your thread I thought you must have been talking about getting arthritis in your hips!
Its fair to say motor cars are a bit like people in that rear ends dont get looked after as well as they should !!

A good indicator is the number of threads where people say how hard it was to remove the diff plug. It must have been stuck a long time!! Maybe from new.
Splines are the least of ones worries, reduced oil volume is likely to reduce lubrication to the pinion & carrier bearings, they will in time let you know.

With most DIY's not having a hoist, its not surprising that rear ends get neglected. You can be sure that there are service tech's that just tick the box without removing the diff plug.
let the truth be known, there would be plenty who only have checked/changed the diff oil because one of the drive shaft boots had to be replaced.
Then there are those on here who will let you know in no uncertain terms when you dont do exactly what the book says.

We should be more concerned if the diff oil started to smell burned at all as this may indicate overheating.

Best of luck with your car !!!! ;)

I can.

If one knows how the important parts of our differentials get lubed... then this idea of ' sensitive' is pretty much a bogus question in the first place. These are slosh lubed machines... if the lube is below the minimum level for the important parts to get lube then you have problems..... Your assumption on the ' tolerance' was a non starter....and then offering up totally different machines to argue your bad assumption with is bad form. You asked a bad question, got a good answer from Brian then used bad judgement in continuing to post.

keep in mind this "80's truck" is a HUGE differential compared to the tiny IRS diff of the MB... it's got giant gears, and HUGE tubes that span the width of the vehicle, also containing oil. they hold anywhere from 4 to 10 quarts of oil compared to the 1ish the MB holds...
why would you ask a question about sensitivity and then get bent out of shape when the response is given?

I was simply inquiring wheather or not anybody else has noticed these differentials to be paticularly sensitive to the level of gear oil. That's it. And instead of that you get jumped on right away like "how dare you assume to question the quality of an MB". Or "what a stupid question, let me lecture you on how a differential works". I have bought/worked on many cars and trucks with high mileage on them where it was fairly clear that the fill plug in the diff hasn't been touched in a very long time, if ever. And even the ones that were low on fluid, sometimes a lot low continued to run for a long time after getting serviced. So the low fluid level must not have bothered them that much! This is the first vehicle I have ever had any differential problems with, I'm just trying to figure out why. I'm sorry if my abbreviated bad name offended anyone.

No one cares about your name. What they care about is you insulting one of the most helpful and knowledgeable people on this forum. If your idea of being respectful to other forum members is calling them an obsenity, then perhaps you should post somewhere else.

now, I don't recommend anybody post on other forums!!!
just everybody needs to keep in mind that TEXT responses are difficult for humans to understand.
see what I mean?

Human Beings are VISUAL communicators. a message may seem outright insulting or demeaning when read by one person, and seem simply factual when read by someone else. it really depends on the mood or frame of mind an individual is in when they are reading. it's why BOOKS are such fantastic vehicles. they spark OUR imagination and emotions.
it's best on a forum to simply read responses, and not take them personally.
it's also why forums usually have the rule not to attack a member for a posted idea or statement, just address or comment on the idea itself.
now, posting insulting words, or images sets the idea right in front of everybody, and that will get members riled!

the response by BC "why would you think that" can be taken many ways, but on a text forum, it's best to just take the information and not take it personally.

I get into trouble all the time with text messages. it seems women and men have different interpretations of words...

now everybody shake hands, and lets try to be helpful and receptive to help!!!
thanks!

also, keep in mind that trucks usually have large profile tires, and short ratio differentials resulting in much lower speed internals in the diff gearing.

our little IRS diffs, and 2.88 or even the 3.69 in the 240 are pretty tall with the little 14" tires!