Which ever fill hole that allows you to get the factory spec'ed amount of oil in (a lift rotates the axle slightly so you can't easily get the spec'ed amount of oil in with a standard fill hole location)

 

Yes, don't rely on the fill holes at all. On the rear a slight slope puts a lot of oil down one axle tube and the level is not that accurate anyhow.

 

On a flat level surface with no lift; rear diff uses the upper port and the front diff uses the lower port.

Key words are flat and level with no lift, factory suspension.


If you have a lift you could still use the ports but you need to lift the jeep by the diffs until you level them off to factory angles. I believe it's 4 degrees measure from the housing spreader pads.

 

I measured my wife’s stock JKU to get the correct starting angle. Then put axle on stands high enough to get back to that angle.

 

Interesting. Every diff I have come across that has an upper and a lower plug, the lower is the “drain” and the upper is the “fill.” Remove both. Then install the lower and fill until fluid comes out the upper. Replace upper plug. Done.
Can’t recall on the D44 honestly though.
Troy

 

The covers being referenced actually have 3 plugs. 2 “uppers” at different levels and a lower drain plug.

 

I appreciate all of the convo on this... I still don't know that I've really gotten a good answer to this question though. When I filled my rear axle, I ended up using the lower fill plug. My plan had been to fill the diff until I hit about 2.4 qts (factory specced oil as recommended by @Bob Sanders ), but when I got to about 2 QTs it started coming out that fill hole... The diff was totally empty as I had the cover fully off and drained for 30 mins, so there was no previous oil left in it to my knowledge. PO had used the lower fill hole as well and I inspected the diff, it seems to be in perfect order. Also want to note that my driveway is extremely flat.

I contacted Dana directly and asked them what the reason for the two fill holes were. Here's the answer I got:

Hello Timothy,

Thank you for you question.

The upper hole is used for initial fill of a "dry/new" axle assembly. Once the assembly has been filled and driven, the lower hole is used to correctly monitor fluid levels and condition.

Sincerely,
DanaProParts.com Support
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To me, that means the lower fill hole is actually what's supposed to be used on a stock D44 front and rear for filling and ensure proper levels with this cover... Is it possible that this cover actually lowers the amount of oil that is needed in the diff because of its design compared to the stock cover?

The middle plug appears to also line up right with the bottom of the axle tube, my understanding is this is the exact level fluid should be up to. Can anyone confirm if this is true? (see attached pic for what I mean).

Does this make sense? or am I nuts?

Also I wanted to point out that the Dana one is VERY different than the AEV one. The dana covers are actually specced specifically for the Dana 44 front and rear. If you look at where the fill holes on the AEV one are, they are in VERY different spots than the Dana one (attached pic below). The Dana lower hole appears to be in the exact same spot as the upper hole on the AEV cover. Also, this makes sense because Dana makes specific part #s for front and rear whereas it looks like AEV only makes a generic dana 44 one. FYI @2katz

Part of me wants to just go buy a set of stock covers so I don't have to worry about this LOL

 

I appreciate all of the convo on this... I still don't know that I've really gotten a good answer to this question though. When I filled my rear axle, I ended up using the lower fill plug. My plan had been to fill the diff until I hit about 2.4 qts (factory specced oil as recommended by @Bob Sanders ), but when I got to about 2 QTs it started coming out that fill hole... The diff was totally empty as I had the cover fully off and drained for 30 mins, so there was no previous oil left in it to my knowledge. PO had used the lower fill hole as well and I inspected the diff, it seems to be in perfect order. Also want to note that my driveway is extremely flat.

I had the same issue when I did my axle. At the end of the day, you can ponder the holes all day long if you wish... but it's really a moot issue. You need to get the spec'ed amount into the diff. Jack the axle up on one side if it makes it easier for you.

When people fill these diffs they always consider oil level at a stand-still, and never the oil level when the jeep is in motion.... and they should because there is a SIGNIFICANT difference with oil level in motion vs stopped. The ring gear scoops up oil and throws it forward to the pinion bearing, which drops the oil level by a fair amount. At 70mpg it doesn't make a whole lot of difference because the oil splash inside the diff is so immense that EVERYTHING is getting splashed but at lower speeds the oil level is low.... AND.... the splash isn't big.

 

On the Spicer site the front and rear units are the same part numbers. There are three p/n but that's for color, hardware and gaskets but the the front and back are the same. The fill holes are higher on the Spicer to accommodate higher pinion angles were as the AEV are set up for the stock height.

The Spicer answer doesn't make any sense to me, why would you have the two ports for that reason. I would question that response from Spicer.

 

On the Spicer site the front and rear units are the same part numbers. There are three p/n but that's for color, hardware and gaskets but the the front and back are the same. The fill holes are higher on the Spicer to accommodate higher pinion angles were as the AEV are set up for the stock height.

The Spicer answer doesn't make any sense to me, why would you have the two ports for that reason. I would question that response from Spicer.

I agree it doesn’t make sense and good eye on the part numbers. I already sent more questions back to them. Thanks for pointing out. Will update when I have more info.

however, would you agree that the upper fill hole is way too high for the stock Dana 44 rear and that the lower fill hole is at the correct height for filling?

 

Easy enough to get a tape measure and check. Which hole is closet to the stock cover?

 

Will report back soon.

 

A good video on what goes on inside your diff while in motion. Note how low the fluid goes while moving slow forward with very little splash towards the axle tube..... and more to the point... how dangerous and disruptive aftermarket diff covers can be if they are not shaped like the factory cover.

 

Very informative. I actually think the Dana aftermarket cover might be the same internal shape as the stock cover.

 

I ended up measuring the fill holes. From what I can tell, the stock cover is about 1 quarter of an inch above the lower fill hole on the Dana after market cover. So, I think using the lower fill hole on the Dana cover after all is incorrect and I ended up going with @Bob Sanders suggestion. I ended up filling the lower hole on both diffs until it oozed out, plugged it, and then used the upper fill hole to estimate the remaining fluid. I am on the lookout for stock covers now...really don't feel like messing with this or worrying about it every time I need to change fluid. My '17 (Which has stock covers) takes like 5 mins to do, this one is way more of a pain. It's also bulkier and the ribs on it make it a pain to fill.

Also, these covers are WAY heavier than stock. I'd rather save on weight.