Well, I am still not sure, but the GAP tool can make a huge improvement on rear diff lock performance!

I have seen this question ask more than a few times and saw, I think so, No, Not sure, Maybe.... you get the idea.

I have complained about my LR3 rear diff not locking when it seemed it should and making a clunk sound if it did engage. I finally decided at some point soon to install a new one. First I wanted a GAP tool for keys and hear LR owners should have one. A near $1k key replacement (FedEx lost then found my only key) motivated the GAP purchase. I called GAP Technologies first and was told a bit unclear answer... GAP tech said, 'If you replace the rear diff locker, just run the rear diff self test and you'll be good'.... or something to that affect. Had GAP shipped in, read instructions, cleared some codes on wife's LR2 and killed it. LR2 stop dead and would not start. GAP support stepped up... Great support brought LR2 back to life and helped define needed service. OK, maybe I can avoid killing my LR3.

The GAP tool is awesome on my LR3 vs LR2. The information provided, calibrations, live data, options.... plus unexpected rear diff functions including locking. Ran rear diff self test even though rear locker was not changed. Incredible difference in every terrain mode. The central and rear locker came on and off smoothly and when needed with no clunking noise. Wow! It was a winner. Maybe luck, I don't know. I do know the LR3 off road performance improved tremendously.

Does the new GAP tool sync a rear diff locker? I can't say for sure.... I can say the GAP tool did something that made this LR3 lock diffs as needed and smoothly.

 

If you have a clunk, it means the rear actor is damaged. You need to do the rear diff software update and replace the rear actuator. Also the rear diff and center and separate systems.

 

The rear diff locker would not or rarely lock. The center lock seemed fine. You could be in sand or mud, steering straight, and center would lock, but the rear would not and now LR3 stuck. Would take multiple attempts to get rear to lock. Your knowledge is far beyond mine and I listened. We even talk about me driving it wrong. But there was one person on the forum that said his LR3 center and rear diff would lock and unlock as needed often and smoothly off road. Now, my LR3, center and rear, locking and unlocking smoothly just prior to expected traction loss keeping it moving forward. The clunk noise was the rear locker disengaging and now gone... no clunk. Although the center and rear diff are on different systems, they are communicating and responding wonderfully. I am a bit afraid of doing anything as it seems to be working correctly.... also know could be only temporary. I think the previous owner replaced the rear diff locker and incorrectly sync or not at all. I do think the GAP did sync rear locker.

Many LR techs say if it's not broke, don't fix it. You still recommend rear diff software update? How do you update rear diff software? (local LR tech was uncooperative about updating last year). Replace the rear actuator? Actuator same as locking motor?

 

I'm glad the clunk seems to be gone...how do you know when the rear locker is supposed to be engaged or not???

 

Going off road on our own land, attempting to go up steep sand hills, a few steep climbs with ground mixture of weeds and sand, some mud areas seemed a good way to test the ability of the LR3. When first bought and drove this bit of land, I could not successfully get over some relative easy sand or grassy areas. The 4x4 dash would show the central locker engage but the rear would not, in any mode, and could not get over the incline... just stuck. After repeating, about the 7th or 8th time, the rear locker would finally engage, then up and over it would go. Bought the GAP tool mainly for key making. After speaking with GAP techs and working with device a bit, I ran some GAP functions tech advised related to rear diff. Did not really expect any real change but why not try it. The locking shown on the dash, central and rear, was quick and smooth. Same hills and conditions, but the LR3 kept moving with ease. No clunk noise. A time or two the central was locked and rear was not and got a little traction loss, the rear quickly locked for added performance. 90% of the time the both would lock before I could tell any traction loss.

So how can I know when rear locker is suppose to engage? I say can not tell when rear or even central locker should. However, driving the same ground with such a difference in performance, the diffs working to spec or least a lot closer to spec, is highly likely. Just hope it stays! Always open and want forum members input.... many, maybe most, have more knowledge than me on Land Rovers

 

...asked and answered. I think that's reasonable, I also think it would be hard to ensure that all variables are the same in making the comparisons.