Just another post agreeing that the 4wd lever on my 2520 definitely has a "lock-in" feel when it engages. And it takes some effort to disengage it - sometimes it is actually kind of difficult to get it out of 4wd. What you are describing sounds kind of like the feel of the differential lock lever on my 2520 - which is located next to the 4wd lever. Per the manual, it will remain engaged only as long as tire slippage occurs. I usually just find myself holding it down with my heel on the rare occasions where I've needed it - box blading & plowing when it's already in 4wd and the tires are still slipping frequently.