Yeah. Toast!

I'll try and JB weld it but that's done for. Almost looks like it was hit at some point.

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Question: If I manually engage the locker with my finger, with the actuator removed from the axle, should the 'diff lock' light go solid or is it sensing something within the actuator itself?

Even though the housing is wrecked, the gear still turns but perhaps it's not turning enough to actually engage the locker.

Edit- As far as the damaged housing goes, It looks like someone tried to remove the actuator at some point by prying from the bottom without removing the top fastener. Wonder if the gear is simply misaligned to it's mate inside the diff. It has worked in the past though and any damage would have been before I owned it.

It's incredibly easy to damage that back plate, even with all the bolts properly removed. Especially in the rust belt. The back plate gets a little corroded, the center part gets a bit wedged in the diff housing hole, and it's all just stuck in place firmly and fragile and brittle.

I thought I was being *super* careful with mine, but after it was off, it was cracked. I just reassembled it again (after cleaning/regreasing) and it's been working fine.

It would be AWESOME if you could buy a replacement back plate, but I couldn't find anything. Just new or used complete actuators for $$$.

IIRC - three's no sensor for locker engagement in the differential itself, it's all in the actuator. A switch closes when the actuator moves to a position that should equate to a locked diff. It's not like the ADD front diff that has a switch that indicates engaged that is separate from the actuator.

Did yours crack as bad as mine was?

Nope - not as bad. I didn't even think I'd cracked it until I cleaned it up. And noticed a semi-circular split around the center.

To a certain extent - the way it installs will hold it together and aligned properly. The center part - that locates and supports the shaft with the gear - goes into a hole in the diff housing itself, so even if broken, that will locate and support that end. Then the rest of the actuator is held on by those bolts. In theory you could get it slightly off center, but probably not enough to make it not work. The main issue at that point would just be water entering the actuator through the cracks. So maybe try to seal them with JB Weld or RTV.

And worse case, if it doesn't work, just buy another one. $400 - $500-ish if you look around some.

Yeah, I figured the same as you that once it's all in place there's really nowhere for it to go... but it's still not working so something must be up. I've already sealed it up with JB so it's not going to leak, I just need to get it working!

Yeah, 4-500 seems to be the going rate. Thats a pretty expensive part that'd I'd prefer to avoid buying. At least until I'm sure it's not something else that is wrong. Like you said too bad you can't get the mounting plate separate.

Thank you for the write up as my light just keeps flashing.
The link to the Toyota grease is now up to $62 but thanks to the naming of the grease equivalent in the Mud link I found this for $9.
https://www.ebay.com/p/1061504266?ii...yABEgLRh_D_BwE

Here are a couple of good ones from other forums that I've found for future reference.

locker actuator rebuild | IH8MUD Forum

Rear Diff Lock not Engaging (3rd-Gen 4-Runner) - YotaTech Forums

I think I might have clocked the gear incorrectly and that is why it won't engage/disengage. I will try to redo it and see what happens, but first I'm going to replace the leaky brake line I discovered while working on this!

Well I won't say I fixed it, but I got it working at least.

Turns out that it had been tweaked enough that it was binding when it was attached to the axle. I had to loosen off the two nuts just a bit so I replaced them with nylock nuts so they won't back off. We'll see how long that lasts but beats 500 bucks for sure.

Just in time too. I was just cleaning up in the shop and my son came to tell me the spot where we had our camper parked was flooding (crazy january rainstorm here today) I had to pull it out of 6" of water on top of ice. Wouldn't have been able to pull it out without the locker for sure.

How?