Is your linkage free but the T-case won't engage?
 

Just in case this happens to someone else.... Last year our 97D1 decided (in the middle of winter) that the Diff Lock would no longer engage. The linkage was free and t-case actuator was moving through its full range of motion. I removed the linkage and moved the actuator with the 13mm nut on top of the t-case to verify function. Regardless, the t-case would not lock in… Luckily we have a few other winter capable vehicles that got us through…. I finally got around to tearing into the t-case and I figured that I would help others out by giving them something to try prior to dissecting the t-case. It turned out that the Diff Lock switch had failed (plunger stuck in down position) and was preventing the carrier from shuttling forward…! So, if you have a Land Rover with free linkage, but the Diff Lock isn’t engaging. Before going internal, back out the Diff Lock switch which is located about 3 inches to the rear of the actuator lever and see if it engages.

Glad it was an easy fix - but who'd have guessed it would be that?

I and many others would, it's a very common fault. Either the solenoid electrically fails or the pin becomes stuck in the bore. Remove the solenoid pin. Just by punching out the pin you'll be able to reassemble the whole thing without any further modifications or blanking plate manufacture.

I know of the failure of the solenoid (preventing low) and the linkage (too many issues to list), but having the "switch" (located where I circled in the picture) for the Diff Lock light fail preventing the spring loaded carrier from moving forward and locking in the front axle was a new one for me that I was not expecting.

Yeah, it's not as common as the solenoid and the fix for that is a to use a very short bolt that is only case depth to fill the switch hole. I don't rely on lights, switches and wires because I'm old school.......read the stick instead. I also lengthened my tc shifter rod so that it isn't a pita to reach, no bending down to reach it day or night. I travel on packed snow covered roads almost five months of the year. We have only two seasons here, winter and tourist.

I thought maybe like me, it's more because you've been driving British vehicles for a long span of time and you've come to realize lights switches and wires contain vast amounts of smoke and should not be trusted.... ;-) If it were mine, a plug would do. It is my wife's winter vehicle and our family loaner.. Sans my wife, I trust the lights switches and wires more then their ability to realize the Diff is locked in just by the position of the stick. :-)


Cheers,
GM

That stupid switch was my main oil leak on the case, think it still leaks some

Now I understand, yes in that case it's important. My truck is not shared which is a very important distinction.

I did the same with the neutral safety switch - bolt.

Tom, did you use Loctite blue on the threads? That works fairly well as a sealant and I'd also check the t-case breather tube. If it's building pressure it's gonna find it's way past anything unsealed when warmed up.

Tom, I'll second the checking of your vent. If you are building pressure in the case, oil will soon find an other path of egress.. I put a copper crush washer (like used on the brake/fuel system) on it. No leaks and the switch functions perfectly! If it fails the same way as the original did, it will be hitting on the radius of the plunger and not the shaft hopefully eliminating the same failure. I verified this with the old failed switch (sample of 1, 100% success).....