quadra drive not functioning

Front wheels aren't locking up when I have wheel spin in the back. I have felt it grab in the front but its ever so often. I have some inner axle seals that are leaking diff fluid ... could this be the reason its not building pressure or do you think the clutches are burnt up from the fluid getting to low after I realized it, because I haven't had time to replaced seals. The driveshaft engages when in 4 lo and spins. I drove up a very steep incline and had back tires spinning in 4 lo and the front tires were almost trying to spin but were squeaking and and kind of shaking or rumbling. Any help would be appreciated ... thanks