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Running EXTRA Gear Oil in DIFF...?

XpedientJ

XpedientJ

NAXJA Forum User
Location
MA
Just installed an ARB rear diff. cover, and may not have determined the correct fill-point on the dip stick.....since it has taken almost 4 quarts.....and, I know it should be more like two....

Can't recall, from distant-past discussions on the subject, if super-filling the diff with gear oil will cause any problems....? Pressure, drag, etc....

Appreciate any knowledgeable input, thank.
 
Dipstick on a diff? Fill hole is where fluid is measured on diff typically
 
OP,

It can cause aeration which doesn't lubricate very well. It can also cause the differential to puke it up through the breather or wherever else it can, like your axle seals. Ideally you'd set it to the same level it was before. If the axle is rotated to adjust pinion angles, you can set it to the same level it was before. I've specifically measured the 8.25 and typically the outer pinion bearing sits in 1/8" of fluid, maybe a little more. Others say don't bother because the ring gear throws enough fluid around it doesn't matter.

Johnnie Walker,

ARB cover has a HIGH fill plug and low drain plug with a dipstick.
 
Yes, thanks very much for the informative reply....

Then, I'w wonderin' if anyone with a stock cover can provide the bottom-of-cover to bottom-of-fill-hole measurement, as I have the ARB cover on and secured. That would enable me to just strike a like-point of level, on the dipstick. Thanks, in-advance, to anyone who can, and will, accommodate.....

{Also, won't mind, at all, stealing-back some of the Royal Purple to use on the front diff....!!}
 
I usually use the axle tubes to determine the height, I prefer them "just" flooded so I get good oiling out to the wheel bearings!
 
The stock diff cover fill hole is about even with the center of the axle shafts. Fill any after market diff cover to the same level.
 
Tim_MN said:
The stock diff cover fill hole is about even with the center of the axle shafts. Fill any after market diff cover to the same level.
Click to expand...

While some covers are drilled that high, it's usually in relation to a rotated pinion, otherwise that's way to high causing issues! Most of the oiling is done by "slinging" or excess being moved about(leaning to one side, going around corners)!

OP, what axle are we referring to?
 
Last edited:
Your owner's specifies the amount and fill level for the diffs. I don't recall exactly what mine says, but I know it doesn't say add until it runs out the fill hole. It's more like 1/4" below the bottom of the hole.

When I do mine I like to try and let it sit for a few hours in between checks so it seeps into any nooks and crannies and I get a more accurate measurement.
 
on level ground, draw an imaginary line from bottom of axle tube to bottom of axle tube, across the diff cover.
Then go up 1/4~1/2" and thats the level you should shoot for.

In a D44 rear thats just between 1.5 and 2 qts.
 
RCP Phx said:
While some covers are drilled that high, it's usually in relation to a rotated pinion, otherwise that's way to high causing issues! Most of the oiling is done by "slinging" or excess being moved about(leaning to one side, going around corners)!

OP, what axle are we referring to?
Click to expand...

Yes, thought I did identify axle: Chryco 8.25

I believe the various aftermarket cover offerings do vary somewhat and, thus, it is the level one is shooting for that should dictate, rather then OE-spec volume....

(AND, to answer one poster: The ARB cover does, indeed, have a horizontal fill-hole in a formed section, and a dipstick on the fill bung.)
 
Well as I already said and was restated by RWK, use the axle tube height +5/16-3/8"!
 
Yes....but, the great mystery is that...I did put in something better than 3.5 quarts, and....I checked today, using the axle-tube center as a reference point, and....THAT is just about where the level is..........

No, nothing leaking-out anywhere. Sure, the rear end IS jacked-up a bit(on jack stands; doin' the disc conversion)...perhaps, THAT is making a level-ref difference...but, of THIS degree?
 
Fill the diff to the required level as already posted, about midway between the bottom and the center of the diff tubes. Pinion rotation doesn't matter, and different diff covers will allow/require varying volumes of gear oil to achieve to the appropriate fill level.
 
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