so i have just finished bringing this car back from the dead. but the second differential is not locking. i havnt really bothered to look at it because there were more important things to get done but now im starting to think. if anyone knows how these work or knows where my problem may be or has some helpful info that would be great. the first one does lock...just the second one that isn't.

 

vacuum leaks.
check your vacuum lines. its all done by vacuum.
also, theres a little plastic type thing attached to the transmission which locks up the front differential. make sure that isnt broken...