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So I changed my engine oil and front and rear diff's while at work today. I have done this a few times before already. Engine went just fine but when I filled my diff's neither the front or the rear took the amount of fluid listed. I put just barely 1qt in the front when it is listed to take 1.35qts and i put 1.9 qts in the rear; again when it is listed to take 2.375qts. I changed the fluids through the drain plug and did not break the covers off. Obviously, I filled both the front and rear until the fluids came out the fill hole and yes the JK was on a flat surface. I remember it not taking the full amounts previously, just thought I would check here.

I'm not missing anything am I? I left both the front and rear drain bolts out for over 3 hours while i went out on an extended call.
 

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If lifted, have you considered the change in camber of the diffs? If they have been changed, then your fill hole is lower then stock. This may be why its holding less.
Also do you have stock covers? Different designs = different fluid quantities.

This is always a tough thing.. everything I have read seems like noone knows for sure what the rules are regarding diff fluid levels.
 

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That diff. angle thing sounds the most logical to me...and if that is the case, I wonder if you are able to get enough oil in the diff...I am interested too, because when I changed mine the first time, I was not lifted...now I am...:shaking:
 

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Nope, my lift is still sitting in my garage screaming at me to install it already:bawling:, so it is still stock. I am going to check the level tomorrow after I drive it home from work in the morning.
 

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That diff. angle thing sounds the most logical to me...and if that is the case, I wonder if you are able to get enough oil in the diff...I am interested too, because when I changed mine the first time, I was not lifted...now I am...:shaking:
I have a 3" lift and had to change the pinion angle. I just used the fill hole for as much as I could get in, and then i closed the plug and put the rest in via the vent tube hole.:)
 

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Diff Fluid Change

I have after market covers with the holes WAY TO HIGH. I just put in the amount listed in the manual for each and let it go at that.
 

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Ok so maybe i am way off. If I have a 2.5 lift and am goign to change to sythetic soon. If i drain adn then fill so it is a littel in the over flow tube will it really hurt anything? or does even th pressure of it comign out the tube hurt something?
 

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I have a 3" lift and had to change the pinion angle. I just used the fill hole for as much as I could get in, and then i closed the plug and put the rest in via the vent tube hole.:)
Hey, thanks, problem solved...:)
 

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Discussion Starter #9
i checked it again yesterday and it was still right at the fill hole on both front and rear so i guess it's good. I'll just keep an eye on it.
 

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Ok so maybe i am way off. If I have a 2.5 lift and am goign to change to sythetic soon. If i drain adn then fill so it is a littel in the over flow tube will it really hurt anything? or does even th pressure of it comign out the tube hurt something?
You won't hurt anything by overfilling it.

The idea of after market covers having a higher fill plug is that you can put the correct amount of fluid in the diff when the vehicle is lifted and pinions are rotated. It does not mean you have to fill them to the fill plug.

Once the pinion is rotated from a lift it is a good idea to add more fluid than stock to ensure the pinion gets lubricated.

I've found that you can put as much as you want in the rear without it venting out the breather. The front is more fussy and will vent if overfilled. Syn fluid seems to expand less than dino and causes less overfull venting issues.

FWIW I run 7.5 pts in the rear and 4 pts in the front.
 

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FWIW, the fluid level should *ideally* be at the bottom of the axle tube. That's about where the stock covers place it.
Ziptie dipsticks work good for higher than usual fill holes. So would a bore scope.
 

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FWIW, the fluid level should *ideally* be at the bottom of the axle tube.
True, unless the pinion is higher than normal. I know the fluid gets picked up the RG and transferred to the pinion, but I've found with the pinion pointing up a lot that the pinion bearings can end up a little short of fluid.
 

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^ And that's where the lubricity vs. friction vs. overfill issue becomes VERY complicated :) Mark W.
Oh I'm sure there is an engineering reason not to overfill the diff, but I've always found that too little fluid can lead to damage, whereas too much fluid never seems to lead to any issues. Besides which more fluid = better cooling and the rear diff gets hot.
 
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