you say there is a ZIRK fitting
is it in the tip of the axle?
if so AND this is a new unit it is a simple operation to insure your bearings are packed and will provide you MANY MILES OF SMILES
i just went thru this w/ a new axle on a trailer
i removed the dust cap by GENTLY tapping the outer edge to dislodge it and grabbed it w/ channel lock pliers to pull it off
https://lh3.googleusercontent.com/c5y-z ... 80-h640-noonce removed I plugged in the grease gun and started pumping
https://lh3.googleusercontent.com/RqgKq ... 80-h640-nothe factory grease is always questionable in my book and i replace it w/ OFF ROAD/WATERPROOF grease from TRACTOR SUPPLY which i use for all my greasing needs(farm tractor & implements, boat trailers & outboard fittings, motorcycle needs, RV wheel bearings, utility trailer bearings, trailer tongue jacks...) and is bluish/green
in this case the factory grease was red
https://lh3.googleusercontent.com/JNXkn ... 80-h640-noand it pumped out easily until what i was seeing was all the new/known stuff
https://lh3.googleusercontent.com/ee2_W ... 80-h640-noonce the factory grease was replaced the wheel was spun vigorously and i listened for any rough/grinding noises
when i confirmed no bad noises i replaced the factory dust cap w/ one thet has a rubber insert in the center which can simply be popped out for future lubing
similar to these
https://www.amazon.com/Redline-Lube-Gre ... r+dust+capsince i started following this procedure(in the 1970's) i haven't had a roadside bearing failure over MANY MANY thousands of towing miles
if you jack the wheel off the ground at the beginning of each season and spin it listening for the above mentioned noises and lube the bearings you will be just fine (for utility & RV trailers)
if noises are heard i pull the hub and remove ALL bearing components, grease and the seal w/ new parts and re-fill with new grease
ANY time a seal is removed it gets replaced w/ a new one PERIOD
some say it is an expensive waste of grease to fill the cavity in this manner butt you only fill it once
further lubes only utilize enough grease to top it off which is just a couple squirts/service
the above procedure used less than 1 tube of grease
btw, the axle i replaced was over 25 years old and the bearings were still sound, it was the axle tube that was in question w/ heavy rust from frequent dunkings in salt water
this is just the way this old man cares for his trailers and their bearing needs
sw