LR4 Factory Locker Swap

Look up this link for the ARB experience in a LR4 - https://www.disco3.co.uk/forum/arb-...long-time-no-update-189750.html?highlight=ARB - but you are correct once you have the bits changing to the LR rear diff lock and then getting it programmed in is a good way to go but you do loose the ability to manually control it like the ARB.
I'd be lying if I said I wasn't completely jealous of that setup! One day when I'm ready to drop a few $ on front and rear lockers.... I'm always a fan of manual locks over auto locking.
 
Finally started doing something last night. I received most of the connectors, pins, wiring, and hardware in the mail, so I test fit everything to the diff lock control module. I noticed early on that the 18-pin connector on the module had opposite index tabs then the other connections. I couldn't find that specific configuration of connector available, so I ordered a couple different configs of the same 18-pin connector figuring I would just modify one. I ended up using a sharp chisel and shaved off the indexing tab from one side of the white one.
ECU.png
ECU_Receptacles.png
ECU_Connectors.png
Connector_modified.png
ECU_Connectors_Mated.png

Just to make sure I got everything right, I went ahead and wired up the 15-pin purple connector. That connector only takes 2 pins for the CAN connection, which are spliced into the existing CAN network wires, so its an easy one.
Wire_Terminated.png
Connector_Purple.png
ECU_Purple_wired.png

Lastly the D38999 connector and AT series connectors also showed up. One of the D38999s is on back order and should be showing up over the weekend. In case you're unfamiliar with D38999s, they're used a lot in aerospace and come in almost any configuration you can imagine. I tried to pick typical ones that were less expensive and available (many are custom made to order).
D38999_Disassembled.png
D38999_Assembled.png
 
Diff arrived today.
Diff, Back.png
Diff_Front.png
Now that its here, I'm re-thinking my plan to add a disconnect bracket and connectors hardwired to the diff for the Lock Actuator plug I cant find. Taking it apart, the little 'bump-out' that the connector is on is just a housing for the connector. I may be able to modify it to use a connector that I can get both sides to instead. I could run a connector out both sides of the housing if needed for space. Getting the temp sensor connector is pretty easy. That would allow for less of a kludged solution, and I may be able to use the extra connectors to act as a bulkhead between the vehicle interior and undercarriage as well (TBD on that idea). I've ordered up some new connectors to play with the diff solution.

Plenty of markings on the diff actuator receptacle. Nothing that leads you to anything online though, just dead ends.
Diff_Acutator_disassembled.png

I also populated the main connector from the diff lock control module (C2164) to the diff actuator and diff temp sensor. This is a ridiculous amount of wiring going to a diff locker.
Diff_Harness.png

Lastly the new power distribution panel, relays, fuses, and main 8ga power wire arrived. Unfortunately, I bought a pre-bussed panel (which I dont want). Ordered a different one, which should be here shortly. Though I have to say, this power panel is really nice. I ordered the same one, just not bussed.
Power_Dist_Pnl.png
 
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Not too much going on lately. I finished wiring the new power distribution panel and its ready to be installed. I decided I'll try these new connectors I bought for the diff. Essentially I'll put two of them into the diff, coming out either side of the connector housing. I drew up the new covers for the housing to be laser cut from sendcutsend and they should be here tomorrow. At that time I'll be able to see if this works.

Diff_connector_new.png
Diff_connector_plates.png

I also got the diff lock control module installed and the main bundle routed from where the power distribution panel will be installed to the diff module. The diff module installs on the backside of the bracket holding the parking aid module. Taking apart the interior is oddly not straight forward, and I wasn't 100% happy with the route of the wires, but it'll work. I ended up poking a hole through a wire gland to access the engine bay. Once the interior was out, it was easy to do. Note that the ground used by the diff module is the back screw of the bracket its mounted to. The diff module is the only thing that grounds to this spot, so no other wires are grounded there, making it a little sneaky.
ECU_Instl.png
C2715S.png
Wire_route.png
Wire_Gland.png
 
Laser cut parts for the diff came in. I'm pretty happy with how they came out.
Laser-cut.png
Laser-cut_2.png
Diff_connector_installed.png

I also finished wiring up the new terminal block and power distribution panel and got them both installed. I put them next to the transfer module.
Terminal_rail.png
Power_dist_pnl_installed.png

Only things remaining
1) wire power to the terminal block from the batt
2) look at wiring passthru from interior to the rear diff to see if I can add a disconnect
3) finish adding the new connectors to the new rear diff
4) install rear diff.
 
Slow progress over the past week. Wired in the new connectors to the diff. The one that bolts in was pretty straight forward. The other side I used some EA E20HP Loctite epoxy to and clamped it to cure. Its solid.
Bolted_Connector.png
Epoxy_connector.png

Pulled the diff out over the past couple days. Honestly, it was horrible. The exhaust needs to come off to drop the diff, but the exhaust is fully welded. I could loosen the connection in front of the first muffler and drop the exhaust to the floor, but I couldn't remove the whole thing. Next, the axle shafts wouldn't back out of the hubs. I used the ol' hammer method, an air hammer, a press....nothing. So I had to just disconnect the entire hub assembly which means paint marking the camber bolts and breaking the alignment. Finally, the freaking driveshaft bolts are torqued to 110ft-lbs and installed with thread locker. Those didn't come off without a fight. And it doesnt help that everything on this vehicle is just so GD heavy! But, its out.
Diff_removed.png

Counted the splines on the shaft and the spines on the new diff. They match up as I was pretty sure they would.
Shaft_Splines.png
Diff_Splines.png

Comparing the diffs. Spot the difference! There is a odd change on the left side of the diff (where the locker is essentially installed on the newer diff). On the old diff, there is a bearing in that side. On the locker diff, its a precision machined shaft the axle slides into. Took some measurements to be sure, looks like the splines are the same depth into the diff, and the LH side, the axle shaft is the proper size and has a matching machined surface to fit into it. Just odd its different.
Diff_Comparison.png
Old_Diff.png
New_Diff.png
 

ChasingOurTrunks

Well-known member
Wow. I admire this post but also am now endlessly grateful that my truck has the factory locker.

My thoughts exactly!

@Grade_D_Angel you are doing this community a service with this post. I'm actually not even thinking of the LR4 but the new Defender; other posters have expressed trouble finding any new Defenders with the rear lockers, and many folks are pulling the trigger anyway. In a few years time, those Defenders will be on used car dealer lots, and the ability to add a factory rear locker (or at least, know the work involved in it -- which I imagine is probably very similar between the LR4 and the Defender, given the design) is a huge asset.

The ARB option is intriguing as well -- I'm curious how the ARB locker would work with Terrain Response or TR2? The LR4 has Terrain Response at least, right? Which suggests that the locker will lock and unlock dynamically as intended. I would suggest that that's the main advantage of going with a factory locker, but that's from a place of ignorance so I'd be curious for more learned opinions on how the ARB works with TR systems.
 

Carson G

Well-known member
My thoughts exactly!

@Grade_D_Angel you are doing this community a service with this post. I'm actually not even thinking of the LR4 but the new Defender; other posters have expressed trouble finding any new Defenders with the rear lockers, and many folks are pulling the trigger anyway. In a few years time, those Defenders will be on used car dealer lots, and the ability to add a factory rear locker (or at least, know the work involved in it -- which I imagine is probably very similar between the LR4 and the Defender, given the design) is a huge asset.

The ARB option is intriguing as well -- I'm curious how the ARB locker would work with Terrain Response or TR2? The LR4 has Terrain Response at least, right? Which suggests that the locker will lock and unlock dynamically as intended. I would suggest that that's the main advantage of going with a factory locker, but that's from a place of ignorance so I'd be curious for more learned opinions on how the ARB works with TR systems.
All LR3’s and LR4’s have terrain response and the later ones (2014-16) with the HD pack have TR2 IIRC and the later ones without the HD pack have a stripped down TR and are AWD (Not permanent 4wd) with no low range. The ARB locker would essentially make the system think there’s no wheel spin on that axle. Ultimately anything can be added after the fact it’s just a matter of spending the money and doing the work.
 
Good news and annoying news.

Good news, locking diff is installed. I didnt take many photos on this since I was just trying to push through to the end. The main harness that connectors the RDCM to the diff routes through the gland that the other harnessing passes from interior to exterior, which was easy. I tied the new harness to the old harness and just followed the old harness path, which routes directly above the diff. I then measured, cut, and terminated the harness.
Harness_1.png
Harness_2.png

At this point, install new diff and hook up connectors. I recommend hooking up the connectors right after the diff is in place. The motor connector(s) is hard to reach as it is and reaching it with the axles and exhaust in the way would be a PITA. Don't forget to also connector the diff breather.

Next I spliced the RDCU into the CAN network. The CAN network is broken into two parts, High Speed and Medium Speed. You want the High Speed CAN, which is two, 20ga wires (yellow w/black stripe, yellow w/brown stripe). There is nothing special about splicing into it. As long as you're splicing into those two wires, everything will talk to each other. I opened up the main harness at the C-Pillar and spiced in.
Splice point.png

Lastly, you need a IIDTool or similar to configure the vehicle.
This is just for the GAP IIDTool. Others may be different. For the IIDTool, you want to find the ECU
Menu > IIDTool Config > Find ECUs.

Once the ECU is found, you can turn it on in the config file
Menu > CCF > IPC-Instrument Pack > Locking Rear Axle Differential > change from Not Fitted to Fitted
Screenshot_2020-09-18-12-31-42.png

This is where the annoying part happened/is happening. Changing the diff locker to fitted immediately throws an fault, P0806, from the RDCU. This fault unfortunately also shuts off the terrain response, ABS, stability control, and a handfull of other features.
Screenshot_2020-09-18-13-20-50.png

Looking this up in the FSM...
Screenshot_2020-09-18-13-28-46.png

So the fault appears to be an issue with the locking actuator. The position of the actuator is different then the vehicle expects it to be. Step one is to calibrate the locker. This isnt totally unexpected, since all the FMS procedures say that if you replace the diff, the locking actuator, or the RDCU, the system needs to be calibrated. I contacted GAP and they sent me a beta build for the IIDT which calibrates the system. Unfortunately, still no dice. I still get the same fault. GAP is looking at the fault logs and the ECU data and will get back to me if there is anything else to try, otherwise according to the FSM the actuator is bad, which would mean pulling the diff all over again :( So TBD on that.

At least on the good news I can pull the fuses which power the RDCU, and the vehicle then ignores the entire system like its not even there, and drives just as it did before. No systems are shut off and everything is happy. So far now, its just a waiting game to determine the next steps.
 

garrycol

Member
I had looked into doing what you are doing a couple of years back - the one thing I would have done though is not to integrate the diff into the cars canbus and other systems and make it a manual system operated from the cabin.

To over simplfy the system, the car detects slip, and applies a voltage to the rear diff that applies a level of lock appropriate to the voltage applied (yes it is much more complex). I cannot remember what the voltages were, but manually applying the voltage for unlocked (assume 0v) , half locked and fully locked manually from a switch in the cabin direct to the diff would make the system manual rather than being fully automatic without input from the driver. A simpler process than the integrated system you are doing and gives the driver just a little more control.

Some people have also considered a similar override switch for the centre diff lock, so that the CDL could be locked irrespective of the TR selection - at present the CDL only fully locks in Rock Crawl.

A great thread which I have followed with great interest.

Garry
 
I had looked into doing what you are doing a couple of years back - the one thing I would have done though is not to integrate the diff into the cars canbus and other systems and make it a manual system operated from the cabin.

To over simplfy the system, the car detects slip, and applies a voltage to the rear diff that applies a level of lock appropriate to the voltage applied (yes it is much more complex). I cannot remember what the voltages were, but manually applying the voltage for unlocked (assume 0v) , half locked and fully locked manually from a switch in the cabin direct to the diff would make the system manual rather than being fully automatic without input from the driver. A simpler process than the integrated system you are doing and gives the driver just a little more control.

Some people have also considered a similar override switch for the centre diff lock, so that the CDL could be locked irrespective of the TR selection - at present the CDL only fully locks in Rock Crawl.

A great thread which I have followed with great interest.

Garry
I had this same thought initially. Essentially you turn it into a e-locker which would be great. But I don't think I could confidently do it though without having a working system to measure the voltages during lockup. Its tough to say what the entire system is really doing, specifically how much voltages is being applied and when. I thought just putting in the full factory system I'd have a better shot at success, but we will see.

One thing that honestly bugs me about the Land Rover is all the electronic, infinitely variable locks. Coming from the Toyota world, I do like things to just be manually locked or unlocked. But, its all part of the package.
 
So I worked with GAP on the issue, and they've been extremely helpful. We tried a few different things, but no dice. GAP tells me this has been done a few times before, and we've run through all the same steps to activate and calibrate as was done before, so it should be working. They have also confirmed the ECU is fine. We agree that all signs seem to point to the diff actuator (which is also recommended in the fault data).

Of course, if the actuator is bad, it begs the question...how good is my wiring job with the connectors inside the actuator....maybe its not 100%, maybe I crossed a wire, or something came loose, or something got pinched.

At any rate, next thing I am going to try is to replace the actuator, but while I'm doing that, I figured I'd double my efforts on finding the diff connector. I emailed a bunch of wrecking yards nationwide with no luck (most dont want to cut the harness). I did learn BMW uses the same connector, and with much, much, much internet searching, I found the holy grail!


I ordered up 2 with a few larger awg contacts. They're shipping from Europe, so it'll be a bit to get here, but I'm excited! With luck, this will make a plug and play without having to do any trickery with connectors.
 

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