Front differential randomly disengaging
 

Ok so here is my problem: I bought this blazer the 4wd didnt work so i replaced the front diff. After first installed it went into 4wd like it was supposed to. Then, one day i tried to engage 4wd, i heard a bang, now i have a hard time getting it to lock in again, but sometimes it will go right in. For the most part I can't get it to lock in when i need it and sometimes it will disengage by itself when im driving in 4wd. To get it to lock in though, i always have to get out, reach under the battery and push in on the actuator. I was thinking it may be the hardened washers in there have broken but im not sure. any help/thoughts would be great.