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Don't use the fill holes on the covers as your guide, you will under fill if you do. From memory, front = 1.35 qts, rear = 2.4 qts. Get as much in as you can through the cover hole, the rest through the vents. I switched to TF covers. They have dual fill plugs, saves the vent fill PITA factor.
 

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Don't use the fill holes on the covers as your guide, you will under fill if you do. From memory, front = 1.35 qts, rear = 2.4 qts. Get as much in as you can through the cover hole, the rest through the vents. I switched to TF covers. They have dual fill plugs, saves the vent fill PITA factor.
The correct amount of diff fluid should fit without going through the vents.
 

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If you use the stock covers' fill hole you will underfill, guaranteed. Try it for yourself. Vent hole filling for a full top up is pretty well documented.
 

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If you use the stock covers' fill hole you will underfill, guaranteed. Try it for yourself. Vent hole filling for a full top up is pretty well documented.
This is the first time I've heard of this. How do you "know" that you are underfilling if you use the fill hole?

Are you implying that you fill the diff to the brim by using the vent hole? :faint: The diff capacities might be true when they were new and "bone dry". However there is quite a bit of residual oil in them when they are drained which makes up the difference between what the book says and what actually fits. Last time I did my diffs I only used 3 quarts, one in the front, two in the rear.
 

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Are we to believe that the Chrysler engineer mistakenly placed the fill port on the diff cover to low? If anything i think that the hole was positioned correctly and the correct amount of fluid was determined later based on what fit. Who's got a service manual? A: what does it say and B: Can i have a copy or it electronically?
 

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Are we to believe that the Chrysler engineer mistakenly placed the fill port on the diff cover to low? If anything i think that the hole was positioned correctly and the correct amount of fluid was determined later based on what fit. Who's got a service manual? A: what does it say and B: Can i have a copy or it electronically?
The axles are made by Dana and are shipped filled with oil, which is added with the cover facing up. The cover is a Dana-generic D44 part and is not specific to the JK housing. If you use the JK's fill holes you'll underfill the front housing by about .4 qt, the rear by about the same. This is worse if you have a lifted rig and corrected pinion angles, which as mentioned above effectively lowers the fill hole. As suggested, try it yourself and you'll get close to the same results.

FSM spec = 1.35 qts, front, 2.375 qts rear. This is also in the owners handbook.
 

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Discussion Starter · #19 ·
...FSM spec = 1.35 qts, front, 2.375 qts rear. This is also in the owners handbook.
That's understood...that info is in the owners manual and well "documented".

You made the comment about using the vent hole to top it off and the procedure being "well documented"...would be nice to know where.
 

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