Ford 8.8 axle filling question

[TerryMason]

I'm preparing to swap a Ford 8.8 into my TJ, and just bought a nice new solid brand diff cover. I've done a bit of reading, and people seem to say that I should only fill this through the factory fill plug. What's the reason for this? Is it to keep me from overfilling it, or will fluid put in through the diff cover not lube all the necessary sections?

 

[Utah_jeepster]

In general you want you axle tubes about 1/2 to 5/8 full of lube, any more and it will blow gear lube out your vent, you need some room for expanding gases

 

[TerryMason]

I was more curious as to why I should fill from the front of the axle instead of the back (through the diff cover). I wasn't sure if filling from the back would fail to lubricate some section (I can't see how though).

 

[steady.foot]

Not sure if this is why they recomend filling it from the front or not, But if you have to turn the front of the axle up in the front to compensate for a lift then the fill hole on the cover will not fill it full enough.
Most rear axles are designed to lubricate the axle bearings with the diff. oil and if the oil level isn't high enough it isn't able to get to them.

 

[TerryMason]

That's a good point. Right now the axle is on jack stands and the diff cover fill hole is higher - that may not be the case once it's installed.

 

[ljrubitm]

I came across this to help with your question. If you look at the pics you can see the dif cover fill hole is higher then the stock fill hole.If you fill from the dif cover hole you will be adding more fluid then needed, Not a good thing.

8.8 Fluid Change and Rockcrusher - 4x4 Preservation

 

[TerryMason]

Sounds good.

What happens if the case if overfilled? Won't it just overflow the breather?

 

[ljrubitm]

You could blow out a seal or two. Not to mean explode, but cause a leak