This may help: https://www.jeepcherokeeclub.com/threads/ptu-service-question.241970/#post-3039050

 

Hi @Sutley92 ,

Welcome to the forum. The unit is called a Rear Drive Module (RDM). There are three variants, AD1, AD2 and AD2Lock, depending on your particular Cherokee model. Regardless of the model there are two fluids used:

1. Gear Oil (specifically, Mopar 70W-80 pn: 68227765AB ) that's used in the pink circled section below. if you have an AD2/AD2Lock unit you actually have two of these sections. The fill plug for this section is on the rear of the unit. Depending on whether you have an AD1 or AD2/AD2Lock unit, you have one or two fill plugs respectively.

2. Hydraulic Oil. The unit responsible for engaging the wet clutch pack uses hydraulic fluid filled from the top of the unit (Mopar pn: 68227766AB) . The reservoir for this section is the flat metal plate you see at the top of the photo below in the white-circled section. This section holds synthetic hydraulic fluid similar to an ATF fluid and is distributed through the clutch side of the unit through internal passages. It is pumped into the clutch pack via. the pump on the left side which you noted in your photo. Also, there's a pressure sensor right next to it. From the description of the area where you found the oil, I think it's more likely it was the hydraulic fluid you saw. If the hydraulic fluid gets low, the pump sucks up air, the pressure sensor then registers the lack of pressure to energize the clutch and then the 4WD error message appears.

Question... what color is/was the fluid? Was it a bright green (hydraulic) or gold/brownish (gear oil) color?

If it is the hydraulic oil, unfortunately, there only access is the reservoir on top requiring you to lower the unit to get the lid off and add more hydraulic oil. There is a vent tube coming out of the reservoir. I'm not sure if it's possible if you could unplug the vent tube, if you could add a small volume of oil through that tube. It might be possible but I don't know for certain if it has any 1-way vent mechanism on the tube.

 

Note that either way you can also add gear oil (Mopar 70W-80) through the rear-facing fill port (AD1) / ports (AD2-AD2Lock). The port is opened with a 3/8" socket. You put in enough until it starts dripping out the port. If you have an AD2 you will have 2 of these fill ports.

For the hydraulic control fluid, this is the vent tube mentioned in the posting above. Again, not sure if you can push fluid in through it but if so, it could potentially be much easier than dropping the unit.

 

Now I see said the blind man. Ok, he removed the sensor and lost some hydraulic oil. Not a good move.
So now he will need to lower the RDM to add hydraulic oil.
The breather hose is for the gear oil chamber not the hydraulic oil chamber.
Take lots of videos, this is Friday the 13th, whatever.

I wish those stupid pop ups would stop messing with my cursor!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

 

Re: The breather hose is for the gear oil chamber not the hydraulic oil chamber.

Thanks @sanghill. I always assumed the vent was for the hydraulic chamber since it was pressurized (the gear oil chamber isn't under pressure so I couldn't see why it would need to be vented) but you could be right. To be honest, I never traced exactly where the vent went to. This winter I will confirm (Rich gifted me his old AD2Lock unit which I have in my shed and will be doing a tear-down on!!!)

 

Thank you for all the info gary! The color of the fluid is that greenish looking stuff so I know it’s definitely the hydraulic fluid. I haven’t had the vehicle long iam the 2nd owner. I’m almost wondering if the previous owner had taken the sensor off and then not tightened it back on all the way. It was fairly loose before I tightened it. So it’s looking like I unfortunately have to drop the whole unit just to top it off… that’s definitely not a fun job I assume. I was hoping it would’ve had some sort of fill. But I appreciate all the info iam new to the jeep world. I guess I’ll have to get to work it would sure be nice to have 4wd working again on these icy Alberta roads haha

 

Hi @Sutley92 , no problem and good luck If you disconnect the drive shaft, it may be possible to lower the unit just enough to get the top fill plate off and top off the reservoir. The official way is to remove the drive shaft from the RDM (as @sanghill noted, make sure you tie it up or similar so it doesn't just droop else you could damage the drive shaft first joint) and remove the driver's side wheel/halfshaft after which you can lower the RDM)

 

Be carefull to keep the drive shaft straight at ALL times or you will damage the joints. This is really important.

 

Thank you both for all the info. One more question. After I drop this and add the fluid, will I need to take it to a dealer to get the service 4wd to disappear after I’m all done? Or will it disappear on its own once the fluid is at an adequate level?

 

The error message should go away on its own assuming there's not another problem in addition to the low fluid.

A couple things...

1. Once you add new fluid you'll need to bleed the system. You'll need an app called AlfaOBD and a compatible adapter to do this. See info here: See post #39 here: https://www.jeepcherokeeclub.com/threads/ordered-a-vgate-vlinker-mc.249899/post-3034014

2. if you do this procedure (dropping the diff), I would also take off the actuator (the other black box on top of the diff) and gently clean the magnet and sensor and then re-install. It can get build-up on it over time that can also cause a "Service 4WD" error message. Also, if you've never changed the regular gear oil before, this is the time to suck it out and replace it as well so it's fresh (will probably last then the remaining life of the vehicle).

 

I've done maybe 30 sets of axles, mostly re-gear, and what the hydraulic???

I'd like to get a hold of one (blown up, trashed) to take apart and screw around with.


Old days in the backyard... Replace them spider gears...

 

This is the app and the procedure you'll need. Because the fluid has run low, air is now in the passages. After you fill with fluid, this routine runs the RDM pump bleeding the air out of the system.

 

Hey Gary I actually just got done doing this, I was able to drop everything thing down maybe 4-5 inches. Enough that i was able to get an Allen wrench socket on and remove the top plate. I didn’t have to drop the muffler I just barely got enough room to get my hands up in there. Dropping muffler would give a person a little more room though forsure. Used a tranny Jack to support the diff. Took a little fighting but was doable forsure!

 

Excellent! Were you able to top off the fluid and bleed it? If so, did the Service 4WD error disappear?

 

Hello I am new to he club and particularly interested in this thread. I have a 2019 Cherokee Limited with the Active Drive 1 and the rear diff is leaking around the pump motor, (just replaced by a dealer). Long story short I don't trust the dealer to touch my vehicle again, ( I won't go into the details), and I want to remove the pump motor and check the O-rings that are supposed to be installed, I have the O-rings on order, and am trying to figure out how to add fluid back in as I am sure it will run out when I remove the motor. Again this is an Active Drive 1 and there is no reservoir on the top of the rear diff. Any advice

 

There's an access plug near the case half seam that I believe is used to top off the fluid on an AD1 however I'm not certain it can be reached without dropping (lowering) the unit. Do you think they forgot to replace the o-ring or do you think the pump just isn't sitting correctly etc.? How much of a leak, can you post a photo?

 

Thanks for the reply! I suspect the O-ring may be damaged/missing. The motor does seem to be seated correctly, ( no gaps ), but fluid is coming from that area. I did use an inspection mirror and saw the plug you are talking about, near the vent but on the opposite side of the case seam. I will have to get back under there to get some picks, but it's leaking bad enough that the bottom of the differential case is wet and also some on the exhaust. And an oil spot on the driveway...

 

Question... if the dealer did the repair and it was still under warranty, as a 2019 are you still under the powertrain warranty or the repair within its warranty where you could take it to another dealer?

 

So on the 2019+ (reservoir-less) AD1 units, there are two hex plugs which I believe are the fill/air bleed ports. You'll notice some sealant (RTV or brown Locktite) around these ports to seal against leaks. Similar ports are actually on the 2014-2018 units but those included the reservoir as well (I'm not sure the reason for the change in design).

I have a 2014 so my service manual doesn't confirm these are the fill holes but it would make sense. Unfortunaly, I can't confirm the procedure but I would assume the hole (is the top plug (#1) an "air bleed" and fill hole or is it just an airbleed/overflow hole and hole next to the pump sensor drain only etc.). The top hole is course if the most important/easiest since any trapped air will flow up and fluid could be filled from there as well.)

 

Power train warranty is 5yr/60k (I think), and I have over 60k on the vehicle. I do have an extended warranty on the vehicle, with a 200$ deductible. My plan is to fix the leak myself if it will be a relatively easy fix, but I'm not sure that is the case. Attached a couple pics, this is after cleaning the differential off good and pulling the vehicle out of the garage onto the driveway.

 

Power train warranty is 5yr/60k (I think), and I have over 60k on the vehicle. I do have an extended warranty on the vehicle, with a 200$ deductible. My plan is to fix the leak myself if it will be a relatively easy fix, but I'm not sure that is the case. Attached a couple pics, this is after cleaning the differential off good and pulling the vehicle out of the garage onto the driveway. View attachment 230437 View attachment 230439

Just to check the easiest first... Are any of the screws easily turned? (e.g. the mechanic didn't torque them down?) Note there are screws to hold the pump to the mount (which I think is only sold with the pump) and then three screws to hold the mount to the RDM assembly. Looks like the leak is coming from the latter.

 

Look for drain plugs and fill plugs with 3/8" square sockets.
I am assuming you are leaking gear oil and not ATF.
My 2014 TH does not have any drain plugs that I am aware of.
There is a fill plug on the rear left and right side of the RDM.
Personally I not think you should replace the pump seals. If you do and the ATM system needs to be bled, then you will need a WiTech.
I just add gear oil to the two fill plugs and regular intervals to maintain proper 'fill'. Fairly straight forward and does not risk harming anything.

 

HI @sanghill, this is different. It's the pump seal (for the pressure clutch plates), not the gear oil fill holes on the rear (aft) side of the RDM (where there's one or two depending on AD1 or AD2). This is the first I've heard of the pump o-ring seal fail. Almost certainly a mistake during the installation process since the pump was just replaced.

 

So, there actually appears to be two o-rings for that assembly. If you look at the bore the pump goes into on the RDM in the photo below, you can barely make out what appears to be two steps/lips in the bore hole. I bet one o-ring (past #10) goes around the center pump bore and then the second o-ring (part #11) around the entire pump assembly-to-RDM mount.

What do you think.... bet a dollar one is missing...

 

Gary, that is what I suspect. I have the O-rings ordered. Sounds like I will have to do the bleed procedure as well?

 

Yes, you'll need to do a bleed. Either at your dealer of AlfaOBD.

 

I assume this will run the motor/pump to purge the air out without setting off the service 4wd fault?

 

To be honest, I haven't needed to replace my RDM so I haven't had to bleed mine. Yes, I would fully assume it runs the pump to bleed air out of the system (hence the need to be able to get to the top threaded port to let bled air out and top off if necc. While I don't have first hand experience, I cannot believe it would cause the Svc 4WD light to activate (this is a required operations procedure that Jeep also provides in their WiTech. )

 

Note, I have a 2014 (with the reservoir) - these are the instructions for by RDM though yours will probably be the same w/o the reservoir of course. The fluid in the 2014-2018 is MS-2155 hydraulic fluid, not 70W-80 gear oil that goes in the gear fill ports on the rear (aft) side of the RDM. I assume the 2019+ carries through the same but you should confirm this (e.g. when the pump comes off you shouldn't see gear oil come out unless they somehow re-engineered the hydraulics to run off of gear oil)

Note, the photo below shows the two o-rings. This is true-color; they come in red and blue and go in their respective positions. I wouldn't be surprised to see you missing the red one...

 

I have the same problem.change fluids and not have 4wdlow, i dont know what to do
Any one knows how to said if thw up actuator is broken

Help here please i need your experiencies