Do you jack up the diffs to properly fill the diff?

[Carve]

I just changed the oil in my Rubicon Dana 44 rear. It only took about 1.5 qts, and the spec is 2.1. I believe this is because I have a 4.5" lift, so the pinion angle tips the diff back, which lowers the fill port. I jacked up the passenger side a bit and managed to get about 1.75 qts in.

Just wonder if you all jack up your vehicles enough to get the "full fill" in there.

 

[csaxj3]

OST

 

[Mr. Bills]

Be careful about overfilling in relation to the axle tubes. You will learn all about leaking axle seals.

 

[Rubicon88]

No.
Stick pinky finger in hole.
Feel the lube?
It's full enough.
Done...
Go wheeling

 

[defenderu]

I dont know the correct answer but something tells me fill it until it comes out the hole and then stop. Just as you would normally.

 

[SvtLdr]

I've often thought the same thing. The OP makes a good point though with the altered pinion angle. As the pinion goes up the fill hole in the cover comes down, effectively reducing the capacity at which the fluid spills out when filling.

I've also found that published "fluid capacities" can vary depending on the source. Plus, measuring the amount of gear oil that actually makes it into the case is no easy task.

I'm interested in what others have to say on the subject.

 

[Carve]

No.
Stick pinky finger in hole.
Feel the lube?
It's full enough.
Done...
Go wheeling

OK...but if you have a lift and have corrected your pinion angle, it'll take a little less oil for it to come out of the hole

 

[Mr. Bills]

If you have a "high fill" [not the same as high capacity] diff cover and/or radically tilted pinion and are concerned that the "finger in the hole" measuring method will result in too much or too little gear oil, take a look at the relation of the bottom of the fill hole to the axle tube in stock configuration and fill to that level.

Examples:

Dana 44 rear

Dana 44 front

Dana 30:

Dana 35:

Do you see the differences in fill levels between front and rear axles?

 

[Rubicon88]

OK...but if you have a lift and have corrected your pinion angle, it'll take a little less oil for it to come out of the hole

That angle won't mean shit.

I say again. If you can stick your finger in the hole and feel lube...it's filled enough.

Angle or not.

Listen...there are some things that need to be dead on balls accurate. Diff fluid level is NOT one of them.

 

[MaximusLJR06]

I just did this 2 months ago. Rear Dana 44 capacity was like 1.9 Liter I think. I measured out this amount of diff fluid and then jacked up the rear end of the jeep while filling it. You definitely need to get the correct amount of fluid in the diff and not do the fill to the hole method after a pinion angle adjustment. Not enough fluid in the diff and the axle bearings may not get enough oil to them.

If I didn't jack up the rear of my jeep i would probably be half a liter short.

 

[Carve]

If you have a "high fill" [not the same as high capacity] diff cover and/or radically tilted pinion and are concerned that the "finger in the hole" measuring method will result in too much or too little gear oil, take a look at the relation of the bottom of the fill hole to the axle tube in stock configuration and fill to that level.

Examples:

Dana 44 rear
View attachment 255184

Dana 44 front
View attachment 255185

Dana 30:
View attachment 255186

Dana 35:
View attachment 255187


Do you see the differences in fill levels between front and rear axles?

Interesting- why is the front lower? I guess that's why the front is lower capacity, but why?

The level of the hole is only half the problem. Volume is reduced the more the pinion is tipped up. Imagine an extreme example where you have the pinion standing straight up vertical. Even if the fill hole is at the same height as before, your oil capacity would be limited to the volume of the bump in the diff cover....perhaps half a quart at most. Our slight pinion angle elevation WILL reduce oil capacity a bit. I guess it's not enough to worry about though.

 

[MaximusLJR06]

Interesting- why is the front lower? I guess that's why the front is lower capacity, but why?

The level of the hole is only half the problem. Volume is reduced the more the pinion is tipped up. Imagine an extreme example where you have the pinion standing straight up vertical. Even if the fill hole is at the same height as before, your oil capacity would be limited to the volume of the bump in the diff cover....perhaps half a quart at most. Our slight pinion angle elevation WILL reduce oil capacity a bit. I guess it's not enough to worry about though.

Front capacity is less because the gear oil doesn't have to travel down the axle tubes and lube axle bearings in the front end. Rear axle it has to do this.

 

[Mr. Bills]

. . . Not enough fluid in the diff and the axle bearings may not get enough oil to them.

If I didn't jack up the rear of my jeep i would probably be half a liter short.

Not enough to be a concern except in extreme circumstances.

An LJ lifted 3.5"-4" is not one of those extreme circumstances.

A TJ lifted 4-4.5" shouldn't be one of those extreme circumstances either.

 

[MaximusLJR06]

Not enough to be a concern except in extreme circumstances.

An LJ lifted 3.5"-4" is not one of those extreme circumstances.

Maybe not a concern, but for something that take 5 minutes, why not do it right? Then there won't be any worry about it down the road.

 

[jjvw]

Be careful about overfilling in relation to the axle tubes. You will learn all about leaking axle seals.

More likely about spitting gear oil out of the breather.

 

[Jerry Bransford]

It's easy enough to add a little more gear lube through the vent tube opening on top if you want.

 

[Mr. Bills]

Maybe not a concern, but for something that take 5 minutes, why not do it right? Then there won't be any worry about it down the road.

So down the road at the next service interval when you pull the plug to check the gear oil level and the gear oil runs out all over the ground because you had to drive your jeep onto blocks to get it in, is that worry free?

A bit too little won't hurt anything. Too much makes a mess one way or another.

 

[Rubicon88]

So down the road at the next service interval when you pull the plug to check the gear oil level and the gear oil runs out all over the ground because you had to drive your jeep onto blocks to get it in, is that worry free?

A bit too little won't hurt anything. Too much makes a mess one way or another.

This...
Just no need to fill up to the hole then hurry and put plug in place.

If you can feel the lube you've got enough. I promise you.

 

[pc1p]

Interesting- why is the front lower? I guess that's why the front is lower capacity, but why?

Because the lube doesn't need to make it down the length of the axle tubes like in a rear-axle application (front axles have wheel seals just outside of the carrier bearings).

 

[MaximusLJR06]

So down the road at the next service interval when you pull the plug to check the gear oil level and the gear oil runs out all over the ground because you had to drive your jeep onto blocks to get it in, is that worry free?

A bit too little won't hurt anything. Too much makes a mess one way or another.

Well I don’t check my gear oil level while doing service, so I don’t have that problem. If there’s no leak, there’s no where for it to go.