I have the BX2680 and whenever I try to lock the rear axle it doesn’t want to engage most of the time. I was moving snow tonight and was trying to back up on a slick snowy curb and tried and tried, finally gave up! This has happened numerous times, I don’t try when the wheel is spinning .. I always stop and try to engage, then if it doesn’t go I’ll crepe forward or backwards slightly and still no luck. Never had a problem with my B7510, what am I doing wrong? I only have 14 hours on!