I would START at the brakes. Jack up the tires one at a time, using the junction of the springs and axle as the jack point. Once the tire is off the ground, you can access the star adjuster from the back side of the backing plate. There may be two slots with rubber plugs. Remove the forward one, and using a flat blade screwdriver or a brake "spoon" adjust the shoes so they just drag the drums.
Once the screwdriver/spoon has contacted the adjuster, moving the tool DOWN will tighten the brakes. Once all 4 wheels are done you can take a test drive.
One test we use when we do an axle service is to pull the break-away pin, activating the brakes. Then using a torque wrench, tighten the lugs to 120 ft/lbs. If the wheel still turns we tighten the brakes.
With a good jack and jack stands you can do one side at a time. We use 4 jack stands and lift the entire trailer for ease, but we have done one side at a time with BIG heavy units.
2012 Copper Canyon 273FWRET being towed by a 1994 Ford F350 CC,LB,Dually diesel.
Airlift 5000 bags, Prodigy brake control, 5 gauges on the pillar.Used to tow a '97 Jayco 323RKS.
Now an RVIA registered tech. Retired from Law enforcement in 2008 after 25+ yrs.