Diff lock not engaging!!

I recently had to climb a long icy steep grass field which I was surprised when the Defender struggled to find grip. My first suspicion was that although I had selected (centre) diff lock, it didn’t seem that it had engaged. Later on flat ground I tested this theory: jacked up one wheel, selected neutral, handbrake off, turned diff lock on .... and the raised wheel turned freely. Suspicion confirmed.
From under the vehicle I fiddled with the linkage and turned the switch on top of the transfer box and with a bit of encouragement and some WD40 the switch freed up a little. Tested the raised wheel and it locked!
So, it seems I’ve found the problem, but the lever still doesn’t engage positively consistently. Is the switch ( on top of the t. box) adjustable; could it be loosened a fraction to make the action less stiff??
Any suggestions appreciated, thanks!

The lever on the top of the box has a D that engages with the shaft. On mine the D in the lever was worn and so did not move the shaft enough for full engagement. Worth a check.

Muddy tree man said:

I recently had to climb a long icy steep grass field which I was surprised when the Defender struggled to find grip. My first suspicion was that although I had selected (centre) diff lock, it didn’t seem that it had engaged. Later on flat ground I tested this theory: jacked up one wheel, selected neutral, handbrake off, turned diff lock on .... and the raised wheel turned freely. Suspicion confirmed.
From under the vehicle I fiddled with the linkage and turned the switch on top of the transfer box and with a bit of encouragement and some WD40 the switch freed up a little. Tested the raised wheel and it locked!
So, it seems I’ve found the problem, but the lever still doesn’t engage positively consistently. Is the switch ( on top of the t. box) adjustable; could it be loosened a fraction to make the action less stiff??
Any suggestions appreciated, thanks!

Click to expand...

What tyres do you have on?

The other thing that happens is the mechanism wears. There are quite a few joints of the kind where pins go through holes and a tiny amount of wear on each of them means that you lose a lot of movement at the end of the process. To fully sort mine out last year I ended up renewing most of the mechanism. There are some plastic top hat washers at one pivot point and you can get a new lease of life just by replacing them but mine had gone beyond that. Then it needed another warning light switch too, as the old one had developed a high resistance. I don't shift in and out of diff lock very often, just the mechanism ratting about as you drive along can create enough wear.

Al2O3 said:

What tyres do you have on?[/QUO

Click to expand...

BF Goodrich AT KO2 265/75/r16 with good tread. I’m sure it wasn’t the tyres letting me down as after all, it did make it up the field, just not as effortlessly as it should. But considering diff lock was not engaged, the tyres and ETC did good.

Brown said:

The other thing that happens is the mechanism wears. There are quite a few joints of the kind where pins go through holes and a tiny amount of wear on each of them means that you lose a lot of movement at the end of the process. To fully sort mine out last year I ended up renewing most of the mechanism. There are some plastic top hat washers at one pivot point and you can get a new lease of life just by replacing them but mine had gone beyond that. Then it needed another warning light switch too, as the old one had developed a high resistance. I don't shift in and out of diff lock very often, just the mechanism ratting about as you drive along can create enough wear.

Click to expand...

With that in mind, I might look at replacing the linkage mechanism then, thanks.

I’ve also just read that the pivot (attached to the gear box) is adjustable; by making it longer it produces more movement at the bottom of the lever, thus pushing the switch further.... I might try that!

Well, it doesn't make more movement (as the fulcrum stays roughly in the same longitudinal position on the lever), it just puts it in a different place, which might be just enough to click you over.

**Fixed!!**
I originally got underneath and with WD40 to encourage it, I manually flicked the switch on top of the T.box which enabled me to use the lever to select/ deselect diff lock. However this was inconsistent and still didn’t feel like a positive switching motion. Furthermore, the diff lock light on the dash was not illuminating when the diff lock did engage.
Time to do it properly...
As access from underneath is tight, I took the gearbox tunnel out ( this, and the refitting was the most challenging part of the job). With the tunnel removed I could easily access the lock lever, switch and all the trimmings. I removed the linkage with the nut at the bottom, on the switch, and with the nut and bolt at the top, and then took the clip off the pivot bar. I unscrewed the pivot bar by two full turns and then reassembled the linkage. Result! It works every time with a nice positive click. Still no light though.
The switch for the warning light was covered in gunk so I generally eased off the wires and unscrewed the switch. Cleaned up the terminals and connectors and gave the switch itself a good clean. Checked the wiring by shorting the two wires together... light works!! Attached the switch and pushed in the switchey bit... no light. Baffled, I reconnected it all and to my surprise, the light comes on when diff lock is engaged and extinguishes when it is not... just like it should be.
After struggling with putting the tunnel back, it’s all done now.
Thanks to everyone for your suggestions.

The parts in the transfer box only select diff lock when they are ready to do so.
All the lever does is set a position in the box that allows this to happen.
It can be that at a stand still the lock goes in but this is just because the parts line up. Most of the time nothing happens when you move the lever.
So to recap, the gear lever its self does not engage the Diff lock [ as a result it does not feel connected ] The box itself decides when the lock actually engages. The light should only come on when this happens and not when you move the lever. [ unless things just happen to line up ] When moving/driving along engagement usually happens quit quickly, a couple of seconds is normal. Hope this helps. Cheers, Tottot.