If I replace the breather plug with a zerk, and pull the adjustment screw out of the front end while shooting it, will that work?
(2006 L3400F 2wd)
I looked at the manual, again L3700, and what you propose might work on 2WD. Behind the adjusting screw there is a Thrust Collar (probably have to remove), the bushing and an oil seal. There is one of these assemblies to the front and rear of the axle beam, pictured on page 6-S17
Now when I look at the manual, it does not show a grease fitting on page 6-S17, servicing 2WD type but on page 6-S7, Front Axle Rocking Force, it shows a zerk and a breather plug for 2WD? It would seem that if you have a breather plug, there must be a grease fitting??
Also, when you reassemble it is necessary to:
Jack up front axle side
Set a spring balance to the front axle flange
Measure the front axle rocking force (Spec = 11-26 foot pounds)
If the measurement is not within spec, adjust with the adjusting screw
Tighten the lock nut firmly
Hope this helps. On a 4WD this MUST be greased as you have a ball bearing on the differential gear assembly and mating pinion teeth.