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Discussion Starter #1
I just changed the oil in the front and rear diffs on my '14 JKR and wondering what others are seeing for a differential fluid fill on these Dana 44s. I've seen the spec quoted at a few values, but the most common for a JK Rubi seems to be 2.375 quarts for the rear and 1.35 for the front. In my case (OEM covers, level ground, pinion angle essentially stock, thoroughly drained) I only got about 1.8 or so in the rear and 1.1 in the front, to the bottom of the fill hole. I wouldn't worry about a few ounces either way of course but 1/2 quart off the spec in the rear and 1/4 in the front seems like a lot (or at least the rear difference does.)

When you changed yours in a similar vehicle what did you see? If I tried to fill this thing to spec it would be grossly overfilled using the OEM fill hole as a gauge.
 

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When I did mine I got the same as you... about 1.8 and 1.1 (level to the fill holes)



I don't know how you're supposed to cram any more in there.
 

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Well thanks, that makes me feel a little better. In my experience factory 'refill after service' specs are frequently way off from reality. Same thing with the NAG1 auto transmission, spec says 5.3 quarts after pan/filter service, actually took about a quart less.
 

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Rubi's have the frt. & rr. Lockers. those take up extra space and can be why the volume is different. Just my guess.
 

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Perhaps the spec is for a totally dry unit. Even after draining there is going to be some in the tubes. I wouldn’t think too much though.
 

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Well.... the first time I changed fluid I noticed they seemed to be drastically over filled (from the factory). I took the top plugs out and it dribbled for a little while before leveling off at the upper plug. My guess is that they're filled on the bench to the noted factory spec before going on the jeep.


Every drive line guy that I talk to though clearly states:
'fill UNTIL level with the upper plug'.
Given that, you are simply not going to get the factory spec'ed amount in.


Personally speaking I think the factory fill is just too much. When my front seals started leaking at about 20k miles, I changed them out and didn't really see too much wrong with them other than a thick build up the normal matted clumpy mess of oil and new gear dust. That to me would seem to be too high of a fill if that stuff can collect like that on the seals. One would think you wouldn't want the level high enough so that the oil is REGULARLY soaking up against the seals. The sloshing around at a slightly lower level than the seals should be quite enough.
 

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perhaps the spec is for a totally dry unit. Even after draining there is going to be some in the tubes. I wouldn’t think too much though.
^^^bingo...
 

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If you do the change when warm, either warm day or warm driven. You can lift each side for about 15 minutes to drain both sides. You will get close to factory fill spec. But not required, just pull the plug and drain. If fluid is not milky, then don’t bother just drain and re-fill.
 

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Discussion Starter #9
The specified levels for the axles and transmission are for a drain and refill, not rebuild from dry. But then again I don't think I have ever serviced a vehicle that took exactly the amount of fill specified in the manual.

The manual states 'to the bottom of the fill hole' and 'do not overfill', so that's what you should go by I'd think (assuming a stock setup.) I've seen posts where someone was so focused on getting every bit of the specified amount of oil in that they added the last bit by pouring it in through the vent hole. That is probably exactly the wrong thing to do as overfill will only cause excess drag and can lead to higher oil temps than the correct fill.

But I have to add, I just did the transfer case where 2 quarts of ATF-4 are specified and to filling up to the fill hole (as instructed in the service manual) took... 2.2 quarts. Just to taunt me I guess. :D
 

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In the case where jeep is lifted and pinion angle has been changed by adjustable control arms or leaf spring shims the stock fill hole will be lower and you will not be able fill it to the correct level, solution is install a pipe street elbow in the fill hole or after mkt. cover with dipstick. This apply s for rear only and extreme pinion lift.
 

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Perhaps the spec is for a totally dry unit. Even after draining there is going to be some in the tubes. I wouldn’t think too much though.

Mine (front) was bone dry when I filled after I did my seals. I cleaned it all out down to the metal (carrier included). It took a 1.1 quart fill to bring it level to the plug
 

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My covers

Just pulled my diff covers after my 500 mile break in for new gears, I do have poison spyder diff covers, when I refilled it took 2 1/2 quarts rear & 1 1/3rd for front, both D44's.
 

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Just pulled my diff covers after my 500 mile break in for new gears, I do have poison spyder diff covers, when I refilled it took 2 1/2 quarts rear & 1 1/3rd for front, both D44's.
That's about right. They take roughly 2.4 qts rear, 1.4 front. You can't get that much in via the stock covers. You have to get as much in as you can, then put in the balance via the breather nipples. Along with strength, another good reason to go with aftermarket covers.
 

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I just changed the oil in the front and rear diffs on my '14 JKR and wondering what others are seeing for a differential fluid fill on these Dana 44s.

When you changed yours in a similar vehicle what did you see? If I tried to fill this thing to spec it would be grossly overfilled using the OEM fill hole as a gauge.
Yeah - I had this problem too. I'm not much of a mechanic (I do better at electrical/electronics). So I bribe 4 people at the local JEEP dealer every Christmas, and it is damn well worth it!

The bribed certified mechanic told it to me this way. The "Specs" are a general number for the "Average" vehicle. The internal volume of the axle is the same for every vehicle. But what equipment is inside that axle can be very different. Different axle ratios use different sized ring and pinion gears. Add in a locker and that takes up a lot more room than a Sport with 3.21:1 gears. Don't get it drained all the way and you'll put in even less. So a Rubicon with a 4.10:1 and a locker will have less room for oil than a sport without any other stuff in the axle.

That made perfect sense to me. I very carefully parked on level ground and filled until it was dripping out the cap, and called it good. And this is probably what you should do.

BEST OF LUCK SIR!

Mike-5 -- El Paso, Texas.
 

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Discussion Starter #15
That's about right. They take roughly 2.4 qts rear, 1.4 front. You can't get that much in via the stock covers. You have to get as much in as you can, then put in the balance via the breather nipples. Along with strength, another good reason to go with aftermarket covers.
You do not want to fill the stock units (assuming they are at stock level position) beyond the fill hole, that will cause an overfill.
 

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Yeah - I had this problem too. I'm not much of a mechanic (I do better at electrical/electronics). So I bribe 4 people at the local JEEP dealer every Christmas, and it is damn well worth it!

The bribed certified mechanic told it to me this way. The "Specs" are a general number for the "Average" vehicle. The internal volume of the axle is the same for every vehicle. But what equipment is inside that axle can be very different. Different axle ratios use different sized ring and pinion gears. Add in a locker and that takes up a lot more room than a Sport with 3.21:1 gears. Don't get it drained all the way and you'll put in even less. So a Rubicon with a 4.10:1 and a locker will have less room for oil than a sport without any other stuff in the axle.

That made perfect sense to me. I very carefully parked on level ground and filled until it was dripping out the cap, and called it good. And this is probably what you should do.
Yes, that makes sense and what I had pretty much assumed, meaning that the manufacturer is not going to figure out the exact fill for every configuration possible so they just provide a generic number. It is not gospel and the bottom line is that (again, assuming a stock setup) you should fill to the fill hole, and no more.
 

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You do not want to fill the stock units (assuming they are at stock level position) beyond the fill hole, that will cause an overfill.
How would one fill beyond the fill hole... without a mess on the garage floor? :eek:
 

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By forcing more fluid in via the breather hole on top. Got to admire the dedication, but... don't do it.
If you have stock diff covers the fill spec is 1.4 qts front, 2.4 qts rear. Aftermarket covers may call for a bit more. You can't get the correct amount into the diffs by the old "fill 'til it runs back out the fill hole" method. This is particularly true if you've rotated the housings to correct the driveline angle after a lift is installed. You'll have to put the balance in via the fill hole. If you don't you'll UNDER fill by about a half quart front & rear.
 

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If you have stock diff covers the fill spec is 1.4 qts front, 2.4 qts rear. Aftermarket covers may call for a bit more. You can't get the correct amount into the diffs by the old "fill 'til it runs back out the fill hole" method. This is particularly true if you've rotated the housings to correct the driveline angle after a lift is installed. You'll have to put the balance in via the fill hole. If you don't you'll UNDER fill by about a half quart front & rear.

Well that's the point of this conversation. The spec'ed amount goes beyond the level of the top fill hole (which makes no sense in the first place), but you can't get the spec'ed amount in without making a mess all over. Even if you manage to get the spec'ed amount in, you will lose some trying to get the plug back in.


Not withstanding, it's hard to believe they would actually mount a fill hole BELOW the spec level. That's just bad engineering, particularly when you consider it to be such an extremely easy engineering faux pas to correct at the factory..... just raise the fill hole on the stock covers.... DONE!
Sooooo... was there a mistake made in the spec'ed amount, or was there a mistake made in the placement of the fill hole?


I should add that I don't think the front level is TOO critical since the axle seals are right there and will be splashed/lubricated with very little movement of the gears. It's the rear diff I believe is the critical fill. The axle seals are located all the way down to the end of the axle tubes so the level MUST be high enough for a bit of oil to flow down the axle tube and up against the seal... otherwise the seal stands a chance of running dry.
 
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