Lock it and turn your wheel all the way to the left or right go in a circle. You can tell if it’s locked or not

 

no, have not verified physically that it's locked or not locked. What's the best/simplest way to do that? Yeah I'll do that in both states (light on/light off) and see what happens.

 

Yes, okay, there is a spring mechanism the pushes the dog clutch to engage with the rear output splines. But that should typically only take a fraction of a rotation to take effect unless the shaft is spinning too quickly for the spline gears to engage.
Not sure what you mean about the dog clutch needing to "unwind;" it simply rotates with the shaft it's mounted on.

 

Sorry, unwind as in relieve the tension between the front output shaft and the diff so the clutch can slide back.

 

just went for a short drive at lunch. CDL lever engaged, lights and tones as I'd expect in normal operation.

The bigger problem is even with the CDL engaged on my short drive even on pavement and normal right-angle turns I was NOT feeling a significant enough effect to be confident I can tell if the cdl was actually doing anything. I'm going to have to find a large parking lot later and do some more driving.

But another question: Is the indicator driven by a switch on the external linkage or is there some internal mechanism that feeds the indicator? In other words should just moving the linkage always activate a switch (meaning my switch might be flaky and just the indicator is incorrect), or is the voltage feeding the indicator light coming from a switch inside the transfer case meaning that the splines have to engage in order to generate the signal.

 

The switch (or in your case, I think it's switches) protrude into the t-case and are activated/deactivated by notches in the actuating rod. The switches can be removed from outside the case, but you may need to remove the central console and the shifter plate to be able to access them.
Don't drive on pavement with the CDL engaged, unless you're driving in a straight line. That's a good way to tear up your t-case pretty quick.

 

Good info, thanks.

Re driving on pavement with CDL engaged... Yep, I know, thanks! Just trying to get a feel for whether there is *any* scrubbing or binding to feel if it's engaged or not.

 

@robh Not really it transfers power equally to both axles so unlike a locked diff you can not tell by spinning a tire. And the Disco will pretty much drive the same with it out or in.

Technically you could test by jacking the back end up and blocking the rear axle it so the tires are just off the ground, with CDL disengaged you should just sit there all the power will go to the back. Engaging the CDL should let you drive off. If you try this use a stack of 4x4 that will just fall under the truck.

Or drop the rear drive shaft and engage the CDL you should be able to drive in "front Wheel" drive.

 

Thanks Richard, that makes a lot of sense and is an easy test.

 

I was able to test tonight using the approach suggested by @Richard Gallant . I verified that CDL engaged light and tones functioned normally when cold. Then drove for about 30 mins and moving CDL lever gave me no response... no light, no tones.

I jacked up under the rear diff and built a stack of short cut-off pieces of 2x4 under the axle.

Got in and with CDL level in disengaged position, no movement as expected.

Engaged CDL lever... no tones, no light but drove off the blocks. So good news there. The CDL *is* actually engaging whenever the lever is moved, just when warm, I get no lights and no tone, so some sort of switch or other electrical problem to chase down.

I appreciate all the help getting me this far. Now I guess I'll take out the center console and as a first step see if the connectors are fouled and try to clean up/reseat everything.