Well, there are several designs of housings mainly due to the manufacturer, correct?

Say If a FORD 9in, FORD is not going to drill and tap fill holes at several levels for different lube call-outs as it would create a parts and costs nightmare. Neither is DANA.

READ THIS - https://engineneeds.com/what-happens...rential-fluid/ - and get back

 

It's a thread on differential filling. How hard can it be and how many different ways is there. We certainly can make a simple issue into something that is more complex than the space shuttle.

 

That's what I was saying, but maybe did not express clearly.

For a 9" pumpkin (and matching housing), it only needs the hole to be at one position, allowing a proper amount of lube at that fill level, to properly lube all 9" gear sets. Hypothetically, if you manage to install an 8" gear set into that carrier, the proper fill level is still the same as where that same hole is in order to provide sufficient lube for those gears, since the gear axes will be at the same positions.

 

A guy who worked for us a long time ago had a really nice '71 Chevy 4 wheel drive. He had trouble with leaks from the front axle. He had it all apart, changed the seals and couldn't find anything wrong. Then one time he was just looking at the owners manual and in there it said that the fill level on the front axle was 1 inch below the bottom of the plug hole. He used a suction gun and pulled out some lube down to about that level and this magically cured the axle seal leaks. Never leaked again.

I'd say that as long as you can stick your finger in the hole and touch the lube that it is full enough. When driving the ring gear is going to throw it around with unbelievable fury and lubricate everything. With that said a little more or a little less probably won't make any real difference in normal use.

 

Wow, I say something then look away for a bit and then all of this. Okay, here goes:

No, it's my guess, and only if it somehow became up to me to guess.

Why?

Why?

I don't think they would have. I'm sure that all of Ford Engineering's fancy college boy engineers know that the gear oil level has a lot more to do with the level that all of the bearings live at than the gear ratio that is installed.

In pretty much all of the common differential designs, gear oil lubricates the gears, and also lubricates the bearings. If the bearings are getting lubricated properly, then the gears (that almost always reach lower in the housing than the bearings) are getting lubricated properly.

I decided to read it, so you all don't have to. You're welcome. I guess I smell what they're stepping in, but their advice in this article seems targeted towards (generating views so they make money on all those ads that are all over that site, as well as . . . ) general knowledge for folks without much experience with this. Some of my favorite statements:

. . . and somehow this "small vent" knows the difference between "minor atmospheric pressure changes" and major pressure changes due to warming and cooling of the differential due to mechanical activity, and it somehow excludes the pressure change from mechanical activity from escaping???

If it is overfilled by 1ml? . . . or 1oz.? . . . or 1qt? . . . or 1gal? They don't say. They do, however, mention this "massive spike in internal pressure"!!! Oh my goodness! This, combined with the "small vent" that is supposedly only there "to handle minor atmospheric pressure changes" somehow excluding the pressure change from mechanical activity from escaping makes the situation sound impossible to fix. Where do they think they air goes when the temperature of the gear oil rises due to mechanical activity? Do they understand that air expands more than gear oil given the same rise in temperature?

What do they consider a "massive spike in internal pressure" ? Did they actually measure air pressure of a differential for this article? How much was the "massive spike"? . . . 50PSI? . . . 200PSI? . . . 1,000,000PSI? The temperature goes up and down gradually. And again with this they assume the "small vent" excludes air from ventilating if the "small vent" somehow determines that the air's motive for wanting to exit is due to warming due to mechanical activity.

"That immense pressure"? What pressure?

Another statement based on their flawed theory about "immense pressure" and a "massive spike in internal pressure". If a seal is indeed "blown" (as they mention four times in the article) by 2,345PSI of "immense pressure" that built up inside the differential in a "massive spike", then yes, the seal 'will not "fix" itself' and "will continue to leak until it is replaced". In reality, there is no "massive spike in internal pressure" nor is there any "immense pressure" from a differential that is slightly overfilled, and like in @DaveMcLain's example in Post #19, most leaks that I've seen from overfilling are gear oil escaping due to stand pressure caused by gravity, not by pressure unless the "small vent" is plugged completely . . . or unless the "small vent" really can tell the difference between atmospheric air and warm air.

For a person with little experience doing this stuff, this article is probably somewhat useful when this person seeks to learn whether or not they should overfill their differential. I believe it is much more useful as clickbait so they can get their advertising money. Back to the point of this thread, this article contradicts itself as well as the original question in this thread, which was:

The article says that:

. . . and:

. . . but then goes on to say:

Which is "technically too much" according to Ford Engineering's fancy college boy engineers.


Now, let's social-engineer readers of this article to come back and get us more page views and ad money:

Translated: You've done the right thing by seeking out information and being careful with your vehicle's maintenance, and you have no idea that we have just given bad advice based on an incomplete understanding of the subject we wrote eloquently about, so you can trust us and come back over and over and give us more views on this and other articles (like this) that also include generic blanket statements based on incomplete consideration of the factors involved with the subjects we are writing about, and/or possibly from just plain bad advice.

I PDF'd both articles and attached them here for when they disappear later. The ads are lost in the .PDF, but as of this writing, the [[url=https://engineneeds.com/what-happens-if-you-overfill-differential-fluid/]overfill differential] article had 15 ads and the [[url=https://engineneeds.com/is-it-bad-to-put-oil-in-a-hot-engine/]oil in hot engine] article had 18.

 

DAMN !
So I guess the correct answer(s) is to guess the required fill and go from there. Throw the LUBRICATION CHART into the CIRCULAR FILE as it was only meant as a decoration.

Original question answered.

 

That article reeks of AI. Taking it with a grain of salt would be strongly advised.

100 years of automotive history seems to indicate that you can fill to the threads in the level port and you are fine.

Some spec level, some spec 1/4” below the threads. Empirically, it doesn’t matter much. Slightly above or slightly below and most differentials outlast the vehicle on the OEM fill.

don’t overthink this.

change the fluid if you like. But if you can stick your finger in the level plug and reach fluid, you are good. The rest of this is academic.

in reality, the location of the level plug has more to do with its relationship to the outer wheel bearings than it does a specific capacity. The capacity is a derived value from the fluid level required to make sure that all rotating parts see fluid. If the fluid level is low, it starves bearings. If it’s too full, it churns and create more drag than desirable, but the fluid churns as part of its normal process.

 

Why?

 

Agree! Maybe with a dollop of human "I don't know what I'm writing about but need to churn something out to get pageviews."

100 years of automotive history PLUS, don't forget, the self-condemned conclusion in paragraph 28 of that supposedly-authoritative article: "The “safe zone” is a fluid level that is perfectly even with the bottom of the fill plug threads when the vehicle is on level ground."

Seriously though, the only time I've seen fill-to-the-fill-hole be an issue is when a seal (usually pinion, sometimes bearing) is just about dead anyways, or when the vent is plugged up.

Yup.

I think there's a design margin here that the manufacturers have naturally chosen:

- Fill hole designed to end up at the fluid level: If testing or real-world reveals that a slightly higher level is necessary, a redesign and countless field replacements of differentials would be necessary.
- Fill hold designed to be above the fluid level: If testing or real-world reveals that a slightly higher level is necessary, only a minor change to the service manual would be necessary.

 

How hard can it be to understand why manufacturers release maintenance and spec manuals?

The OP asked a service question and it was answered, correctly. If one decides to service his particular vehicle (and pray he/she/it/mutant/gray is not a line tech at some BFH-HOT WRENCH back alley shop somewhere), so be it.

Why the constant b!tching? If you feel your method(s) is better, the manufacturers are always hiring in their engineering divisions.