Can you overfill front differential?

OK... so this may be a newbie question and I searched but couldn't find anything on this. I replaced the front D30 Differential Cover while changing the gear oil ~ 2 weeks back. I used a LubeLocker gasket and a cover that has both a filler and drain hole so I shouldn't have to remove it again when doing the gear oil change.

However, the filler hole on the new cover is about 3"-4" higher than the OE cover w/the rubber plug. I filled it until the fluid started to come out and then sealed it w/the plug.

So now my question... I don't remember exactly how much gear oil I used but it was ~ 3 bottles. I have noticed some wet fluid around the bottom of my '01 XJ and wasn't sure what it was. It was covering the Drivers Lower Control arm, the vacuum tubing and the front driveshaft. I also noticed the vent tube that comes off the top of the differential housing is wet and it's even wet w/fluid at the end where it vents into the engine bay. At first I thought it was coolant because it's sorta green but there are NO coolant leaks and upon further inspection tonight I believe it's the gear oil coming out the breather tube then running down and getting all over the driveshaft and other running gear... which also throws it around while driving down the road.

Is this what happens when you overfill a differential? I know I've overfilled my AW4 transmission one time and it started pushing fluid out the dipstick tube.

Input is appreciated. Can I damage any bearings or my gears? Should I just drain it out and put in a specific amount of fluid and not do it until the fluid starts to drain back?

Thanks for the input.

You should only fill it up to the level of the factory hole. It takes about 1.5 quarts. I am not sure how you can remove the excess short of trying to shove a tube in there and pumping out somehow. It is likely easier to drain and refill. I use the Fel Pro gaskets instead of the fancy Lube Locker. They are about $4 at the local parts stores.

Use the drain plug and let it all drain out, measure the correct amount going back into it, done.

Thanks. Will it do any damage driving it while it's over full ... or will it just keep making a mess? I can't fix it until after I drive it to work tomorrow...

It will expand out the vent tube like it did, and bring down whatever junk is inside the tube when it cools down again

Normal routing for the breather tube is along the driver UCA and up the firewall, zip-tied to a hard line next to the brake booster

The gear oil could foam up and not properly lubricate. I would not drive it any more than I needed to with it so overfilled. Others have done it and I haven't read about their differential failures later, but it can't be good if you know what I mean.

It is like a stormy sea inside the diff while your driving, a little extra fluid is unlikely to hurt anything if the vent is open.

A lot extra and your guess is as good as mine. If it builds pressure as the oil heats up and expands, bad things happen.

Thanks for all the input! I'll drain out the fluid and refill w/the correct volume.

I think what may have brought it more to my attention was the fact I had to drive ~ 50 miles on the interstate yesterday @ 75mph. That's the first time I've driven on the hwy since doing the fluid change. Most of my driving is around town between 35-45 mph.

I overfilled both of mine last time I changed the fluids. The extra "burped" out on my drive from Houston to Big Bend. I thought I was going to have to replace the seals, but its not leaking now and the level is good now.

Easy peasy to change out fluid w/the new Dif Cover's having both drain and fill plugs. Took me about 20 minutes to drain out the new/old fluid and refill w/new proper amount. Put in ~ 1.4 quarts. So far so good... now after a few week of driving I'm hoping all the old fluid I couldn't get cleaned off will 'self clean' so to speak.

The new covers tend to have the fill port higher because they don't know if people will be putting an axle at more of an angle or not (at least that's the reasoning I read somewhere). Always try and put in the correct amount or at least close. A little extra won't hurt (excess from that will burp out the vent tube...sort of like how some of modern coolant systems will just spit all the extra out the side of the car ). A LOT extra may cause some issues (the little vent tube can only vent so much at a time). If you are worried about it, it's not too hard to pop the cover off and refill.

The correct oil level is not determined by the fill hole location for most, yes stock they locate it correctly for stock caster, level ground, etc. But once its lifted or on a hill, or aftermarket covers, etc. That goes out the window.

The correct level is best thought of as...
Draw a line level to the earth (on level ground is the best way to do this :rof: ), straight across the cover from bottom of axle tube to bottom of axle tube on opposite side. This should be at the bottom of the axle tubes. Then measure up 1/2", thats is about as good as you can get to being good for oil level in a front or rear Dana diff. This will never leave you with too much nor to little oil in a diff.

Ressurrecting this thread for a minute. I just did my d30 front diff fluid and filled it till it was coming out the drain plug hole. Jeep was parked level. Is this correct?

Also, when replacing the fill plug, should I put anything on the threads. I've read both (use nothing, use something) If yes, what?

On another note, I did this because I have seen fluid around my driver side steering knuckle. I recently had the knuckles replaced and am worried about an axle seal leak now. The pass. side knuckle is dry. Does anyone have any opinions on this. Maybe just a bit of fluid leaked out and its all good but not sure.

Thx y'all

Filing until it comes out is fine. Nothing is needed on the threads.

Fluid on the steering knuckle almost always means a leaky axle seal. Sometimes when the shafts are removed and reinstalled into a dirty tube dirt is picked up that interferes with the seal. I my experience a leaky axle seal problem will not go away though it may not get worse right away.

It's a miracle axle seals don't leak more than they do... Those springs are very easy to knock off.

X2, you probably messed up the inner axle seal on reassembly... Or maybe it was it's time to go.

Overfilling a diff is possible tho... Especially on aftermarket diff covers with raised fill holes. A good reason to fill to specs, not by feel (til it pours out)

To add to what xcm said, my post from 3/2/16 was referring to a stock differential cover. If you have an aftermarket one, with a raised fill hole, you only fill to the correct level/quantity.