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Old 11-02-2019, 08:50 PM
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How much fluid did you get into your differentials?

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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Old 11-02-2019, 10:34 PM   #2
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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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Old 11-02-2019, 10:48 PM
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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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Old 11-03-2019, 07:07 AM   #4
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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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Old 11-03-2019, 07:54 AM   #5
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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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Old 11-03-2019, 08:17 AM   #6
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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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Old 11-03-2019, 10:12 AM   #7
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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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Old 11-03-2019, 11:05 AM   #8
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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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Old 11-03-2019, 02:30 PM
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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.
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Old 11-03-2019, 02:50 PM   #10
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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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Old 11-03-2019, 05:52 PM   #11
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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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Old 11-05-2019, 07:22 PM   #12
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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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Old 11-05-2019, 07:40 PM   #13
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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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Old 11-05-2019, 07:42 PM   #14
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Originally Posted by smiller1 View Post
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.

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Old 11-05-2019, 07:45 PM
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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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Old 11-05-2019, 07:47 PM
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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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Old 11-06-2019, 10:51 AM   #17
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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?
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Old 11-06-2019, 11:49 AM
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How would one fill beyond the fill hole... without a mess on the garage floor?
By forcing more fluid in via the breather hole on top. Got to admire the dedication, but... don't do it.
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Old 11-07-2019, 07:54 AM   #19
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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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Old 11-07-2019, 08:11 AM   #20
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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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Old 11-07-2019, 09:39 AM   #21
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Old 11-07-2019, 11:34 AM
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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.
The only case where the fill hole may not be accurate is if you have rotated the differential (or perhaps with some kinds of aftermarket covers, can't address that due to the amount of variation), otherwise for a stock configuration the fill hole on the cover is the proper amount of lube, any higher is an overfill. An overfill will result in excess drag and foaming, probably resulting in higher oil temps and poorer lubrication.
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Old 11-08-2019, 12:48 AM   #23
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Axle fill capacities taken directly from the owners manual and the official Jeep Field Service Manual for JK:

Front Dana 30 2.1 pints / 1.05 qts

Front Dana 44 2.7 pints / 1.35 qts

Rear 4.74 pints / 2.375 qts

Underfill at your own peril, gents. Put the remainder in via the breather and you wont be sorry.
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Old 11-08-2019, 01:31 AM   #24
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I've had some grief on this with my front diff. It was overfilled from the factory, as evidenced by all the oil that came out the vent tube on my (long) drive home from buying it. Seemed to have cleared itself out after that, but I had the dealer refill it to the correct level (and wipe off all the mess) under warranty since it had been spewing oil when brand new.


Then not long after that I changed over to an aftermarket diff cover, poison spyder bombshell in the front. I filled it up to the fill hole, as I was lead to believe this cover was designed for that. I bought it new well after they had replaced the old design that I guess didn't have the fill hole at the factory level. But it vented again.


Then later I drained and refilled it and was more careful about measuring the quantity of oil added, did it per spec. But lo and behold it ended up pretty close to the fill hole as expected. And then it vented again. I haven't had any other trouble with the axle so don't suspect something's messed up, and everything looked fine inside the diff when I changed the cover. I have just assumed that after that first hot venting it sorts itself out and is good to go, but should I be more worried about this? Been driving on it like this for many thousands of miles at this point. It's still under warranty but I'm not sure what the dealer would do if I tried to complain about it, especially with the aftermarket cover on there I could see them wiggling around any questions unless some obvious mechanical problem was showing.
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Old 11-08-2019, 04:35 AM   #25
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must be just red ones! mine did the same thing (with ps covers)would only puke oil after sustained 70+ on freeway. I was on a long trip and monitored the leak until it quit. It ended up a tad under the hole. Have put thousands of miles on it since no issues. In flat ground and cold oil is level with the bottom of the tubes. I only use the spec to give me a ballpark figure on how much oil to buy. I say just fill up your boxes until they are just below the hole and you are golden. Don’t see how an ounce or so would make a difference. I have seen ones with a leak lower than that with no issues. I have a stock drivetrain so this applies to that any mods changes things.
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Old 11-08-2019, 07:26 AM   #26
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The only case where the fill hole may not be accurate is if you have rotated the differential (or perhaps with some kinds of aftermarket covers, can't address that due to the amount of variation), otherwise for a stock configuration the fill hole on the cover is the proper amount of lube, any higher is an overfill. An overfill will result in excess drag and foaming, probably resulting in higher oil temps and poorer lubrication.

So you're saying the spec'ed fill amount is wrong?
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Old 11-08-2019, 09:18 AM   #27
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Old 11-08-2019, 12:30 PM   #28
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30 front, 44 back, sport with 4.88s. solid differential covers with higher holes in them. So 1 qt in front 2 qts in rear, because gear oil is sold in 1 qt containers.
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Old 11-11-2019, 12:20 AM   #29
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Quote:
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Underfill at your own peril, gents.
The same could be said for overfilling. The information shown below was copied from my owner's manual.

Quote:
Front/Rear Axle Fluid

For normal service, periodic fluid level checks are not
required. When the vehicle is serviced for other reasons
the exterior surfaces of the axle assembly should be
inspected. If gear oil leakage is suspected inspect the
fluid level. Refer to “Fluids, Lubricants, and Genuine
Parts” in “Maintaining Your Vehicle” for further information.

Fluid Level Check

Lubricant should be at the bottom edge of the oil fill hole.

Adding Fluid

Add lubricant only at the fill hole and only to the level
specified above.
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Old 11-11-2019, 03:19 AM
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So you're saying the spec'ed fill amount is wrong?
I'm only saying that that an after-service fill may not equal the full spec'ed amount for several reasons, as have already been pointed out in the thread. There's really no good argument for doing something like forcing additional oil in via the vent hole since the fill instructions in the manual are quite clear, and besides why would the manufacturer place the fill hole in a way that prevents a correct fill? That doesn't make any logical sense.

Bottom line, follow the manufacturer's service instructions to fill to the bottom of the hole, it's not any more complicated than that.
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