[Gary Kline]

Bleed it with a wiTECH.
Which Cherokee do you have?
Only the Trailhawk uses ATF fluid.

The other day I noticed a weep from my RDM (need to check again to confirm the side but from all the posts, it seems like the left is the one that tends to go). I'm not sure how long it's been weeping (I'm not the original owner) but after viewing this and other threads regarding the RDM gear oil, I'm going to check and fill it this week.

Question to those who have had this issue:

• I have a 2014 TH (AD2) so is the right side the Mopar gear oil and the left side ATF4+? Would seem odd especially since some of the posts mention the fluid migrates from the right to left side. Or is the entire unit the gear oil?
• The posts mention it's difficult to access the fill plug on the left side due to the exhaust. Is it still able to be removed with the exhaust as-is or not really? If not, has anyone been able to do it by, say, suspending the exhaust and removing from a hanger or similar etc.?
• Mine has never been done (168k miles) but never had a problem either. Would you top off the fluid or do a full change?
• If the seal needs to be changed, any idea of what the dealer would charge? (shop time) Do they have to drop the RDM and open it to swap the seal or the seal can be changed on-car?)

Thanks

 

[Gary Kline]

Thanks @sanghill, great info! So, internally, there are two completely different cavities, right? The gear oil for the shafts/splines that is passively lubricated and a completely separate sectioned-off cavity for the ATF for the motor/pump/sensor/top cover?

I'm only weeping from the left half-shaft seal so with any luck I shouldn't have to drop the RDM and can just fill from the fill holes (unless after opening them I find the unit ran dry and I've got a bunch of metal where the drive/pinion splines used to be in which case I'll probably be crying 😭 LoL). Seriously though, I'm hoping that's not the case because if I had damage, I would think I'd hear grinding or feel some binding etc. and it's working perfectly. The only thing that piqued my interest is that I saw some caked on oil/dirt around the left side where the half shaft attaches.

I also saw the posts here about wrapping the tailpipe in insulation so the heat's not directly radiating onto that side of the RDM (and possibly making the seal, soft) so I'll do that too when I check the fluid.

One last thing I found (and perhaps this is known already on the forum but I just missed it), is that the vent tube appears to be only for the AFT chamber, not the differential. So if there's pressure forming from the exhaust heat in the diff, the vent doesn't appear to be involved. (see photos below).

Regarding filling if the ATF is drained through the sensor or pump openings, apparently there's a fill line in the top reservoir so I assume it would be almost impossible to try and fill the ATF by pumping ATF IN through the vent opening somehow (not dropping the RDM) since there would be no way to know when it would be properly filled other than draining it dry and pumping in the exact fill capacity specification. Even so, the vent opening in the diaphragm gasket appears to have a dirt sieve in it which would require any attempted fill operation to be forced through the sieve (in the wrong direction). The upside for me is that I don't seem to have any weeping around the sensor/pump/top cover and everything is working fine there.

Thanks again for the info!!!

 

[Gary Kline]

This is one of my Posts: vent tube in LR wheel well
This is my Post about insulating the tail pipe. Rear axle weep
In my opinion, after doing it, insulating the exhaust pipe serves no useful purpose.
Refer to your last picture above:
The vent with the red cap is for the gear oil portion of the RDM and vents to the left rear wheel well behind the splash panel.
The vent on the black cover is for the ATF chamber, I don't know where it vents to.
Exhaust heat does not contribute to building up pressure in the RDM, I tested for that.
The axle seals on the left and right are the same. The reason why the left side weeps/leaks is because the oil level on the left side is higher.
This is because the oil migrates slowly from the right side to the left side.
Once I filled both sides completely full to the bottom of the fill holes. The next time I added oil the oil poured out of the left side. I had to add oil to the right side.
If you remove the left fill plug and no oil comes out it is really low and the right side is probably close to empty.
When you add gear oil measure how much you add to the left and right side separately.
You should be able to add more to the right side than the left side, if not then probably the unit is nearly empty.
Use the measurement marks on side of the bottle.

Go ahead and add gear oil to both sides, think positive.

Thanks @sanghill, your experience (and everyone's on this forum) is worth more than 99% of the dealers out there whose first call is: "replace the unit and we won't guarantee that's the problem".

Yes, I saw your two other posts; they were my go-to for learning about the RDM oil weep issue. I went out today to take another look (externally), the right side of the case is dry but the left has major weeping to the point where oil has coated the bottom of the carrier casing. Strange that there's absolutely no issue sound or driving-wise and no "SVC 4WD" light. The only thing I can think of is that all my driving, 100%, is paved roads. I only engaged 4Low one time in this whole past year just to test it. Either way, I'm going to do an immediate check tomorrow per your instructions above and fill (keeping note of the refill amount to know how much I was down). Thx.

 

[Gary Kline]

So I guess it's not as bad as I had feared. I opened the right side plug today (the left is still sitting with a rag of PB Blaster on it) and while the fluid was low from the weeping, it still looks like there's some in there and importantly, it looked pretty clean. There's not much build-up around the magnet too.

I have an endoscope camera so I was able to take a couple photos of the gears right inside the right fill hole and I guess from what I'm seeing it's not bad for 2014 with 168k miles on it and no RDM fluid change so far. I'll pickup some Mopar fluid today and suction out what I can over the weekend and then refill.

After that, onto the PTU (which I'm not looking forward to b/c of having to remove the middle skid plate, heat shield etc. and it's 33degrees out brrrr!

 

[Gary Kline]

Sorry I'm late to the party. 2017 TH. Is the fluid level inside the passenger side rear diff plug supposed to be up to the bottom of the fill plug hole?

Yes. Both plugs, right and left seem to be to the same (common) reservoir so it shouldn't matter which overflows first however as some have noted, it appears fluid 'migrates' to the left side from the right. Both should come to the bottom of the fill hole.

 

[Gary Kline]

Thank you for the fast response on an old thread. Let me fill in some blanks. We took the jeep for service friday. As soon as we got it back we noticed the rear axle acting like it was stuck in posi. The passenger side plug had evidence of removal. I took the plug out and could not see oil in the diff. I stuck my pinky down in there as far as I could and could not reach the oil level. This tells me what the problem is. What say you?

Hi @17cherokeeth. Yes, having no or low oil in the RDM is a big problem. If you search for "RDM" and "weep", there are several good posts on this forum from @sanghill where he goes into the fairly common issue of weeping seals on RDM's. This can account for fluid loss in cases where there's no direct evidence, say, of a compromised case etc.

Here's a photo of the inside of my RDM (right side hole) once filled with new gear oil. It should come up to the fill hole. Also, only use the Mopar gear oil. It's not made in the required weight by any of the other major gear oil manufacturers (e.g. Mobil 1, Penzoil, Red Line etc.)

Second photo is of the oil (brown) oil that came out and fill plug magnet residue (not bad).

ps: Since you mentioned you just took it in for service but the plug had evidence of removal, did you bring it in to have the fluid/level in the RDM checked? If so, maybe they drained it but forgot to fill. Either way, taking that plug off I wouldn't think is part of a normal maintenance call.

 

[Gary Kline]

Hi @kalitrailhawk , search this forum for RDM change fluid. Lots of good information and full details/procedure already posted.

Three things to note,

1. The RDM uses a weight of oil that can only be obtained from Mopar . No one has found the correct weight in an aftermarket brand (AutoZone, Advanced Auto etc.)

2. It's filled/drained through the check plus. You need a 1/2" socket head to open it (like on the end of a 1/2" ratchet). Depending on model, you may need a swivel or extension due to clearance with the left side exhaust pipe. It can be done though.

3. If you don't have a hand pump yet, go to Harbor Freight and get their orange-red $6 pump. Works great .

 

[Gary Kline]

Reference #2 above, I am pretty sure it is a 3/8".

Refer to: Is this normal for rdu? Post #5.

Thanks, could be. I can't recall.if I used my 1/2 or 3/8" rachet but is is the size of a standard rachet/socket driver end (definitely not 1/4")

 

[Gary Kline]

Hi I have a 2019 trailhawk. I called the dealer. They told me that there is 1.23 liter of differential oil and 439ml of hydraulic oil. They did not want to tell me where tu put them. There are 2 fill plugs. I filled up the right plug and the left side was not full. So I consider that both sides don't communicate. If they were why putting 2 plugs?
But where goes the hydraulic fluid. Mine is leaking by the right top cover called the actuator.
Thank you for help on this.

Hey @helbob888 ,

The differential oil goes in the two fill plugs that face the rear of the car towards the muffler (the TH has 2 fill plugs because it's an AD2 model, Cherokee's with an AD1 rear drive unit only have 1 fill plug).

When you mention you have a leak, is it around the actuator or around the hydraulic reservoir? Both have seals around them that are replaceable if needed (though you need to drop the RDM to get at them as they're on the top of the unit.) Note on a 2019 you may not even have the reservoir anymore. Can you confirm where you see the leak?

 

[Gary Kline]

I think the plugs are not 1/2" square but 3/8" square.

Oops, typo. Yes, 3/8 square. If AD2, one one you might need a swivel or wobble extension to get around the framing/RDM metal.

 

[Gary Kline]

Hi, thanks you for help. The leak is around the actuator cover, right side. Where goes the hydraulic fluid. The parts guy told me there is 439ml of hydraulic fluid. But couldn't help to where to add it.
Also i filled up the right plug but when t removed the left plug it was not full. Does both side communicate or not?
Thanks

• The Actuator cavity has normal 70W-80 gear oil. They sell the gasket for the actuator separately (however it's unusual that it's leaking from the top???). I wonder if someone removed it? You could try tightening the four screws (and if worse came to worse and you couldn't get a gasket, you could always use RTV to make one.

• The right and left fill plugs lead to one more or less continuous body/sump however there's the ring gear and other gears that don't allow it to freely move back and forth easily. Oil added to the right side will migrate to the left slowly.

 

[Gary Kline]

So you are telling me that the same diff oil goes in both sides. I guess full is when oil begins to overflow

Yes and yes. "Full" is the bottom of the fill port threads for both holes.

 

[Gary Kline]

As per picture, leak is just below the black top actuator

Using this photo, can you draw an arrow tot he exact location your leaking is at to make sure we're talking the same thing?

 

[Gary Kline]

Hi, my leak is from the right top cover(actuator). What type of oil is in there?
Is it hydraulic or it's the same as diff oil.
Also do you have a link or procedure for dropping the RDU in order to access the top.
Thanks for help

Yes, will send you a PM.

 

[Gary Kline]

Do the 2 rear axle shafts come out easily only by pulling them out just like the front on the transmission

Yes. Note...

1. Like any half-shafts, do not pull on the shaft section alone. Either use a half-shaft puller or pry bar to dislodge the cage (inner part with the grease) from the c-clip on the stub shaft holding it in. If you pull on the shaft, you'll pull the shaft out of the cage (probably tearing the boot in the process.)

2. Depending on how much rust you have on your RDM, the half shafts may be rusted to the stub shafts in the RDM and when removing the half-shafts, the RDM stub shafts may dislodge and come out too leading to high heart rate, palpations and a general feeling of, "OMG, did I just f#@$ something up????" The stub shafts pop back in. Note, this tends to happen most on the driver's side where the stub shaft is short (~6"). The passenger's side is much longer, about 15". In the photo above, you can see the driver's stub shaft and black dust shield at the left side of the photo. If it comes out, you can just put it back in when reassembling.

 

[Gary Kline]

Here for example, this is when I removed my driver's side rear half-shaft. Note the RDM's stub shaft (and dust shield) came out as well as the splines on the male stubshaft rusted to the female splines on the inside half shaft. No worries, the stub shaft just pushes back in and it's c-clip (in the groove at the far right end) engages inside with the RDM's gears just like any drive shaft replacement does.