got a serial number of this unit handy?

generally if there is not an access hole on the outside of the hub then there should be a rubber plug (if it has not been removed) on the lower part of the backing plate.
This will require you to put blocks under the mast and tilt forward onto the blocks to get the wheels off the ground. (make sure you block the steer wheels so the truck will not move while you are underneath the truck).
Then reach around the wheel and feel on the bottom side of the backing plate around where the parking brake cable goes into the backing plate, you should feel a oblong rubber plug or a hole where the adjust wheel is just inside the backing plate hole.
You can remove the wheel to make this easier if you like.
The manuals method for adjusting brakes
make sure the parking brake is fully released, then adjust up the adjuster to tighten the brake shoes till the drum starts to drag, then back off the adjuster about 1/4 to 1/2 turn or so (generally about 15 clicks), the drum should turn freely after this adjustment. (do this for both sides)
Then you can reinstall the wheel and then check the brake pedal and master cylinder adjustment and set the pedal free play if needed.

A similar but alternative way of adjusting brakes
If the wheels are loose and the brake pedal has alot of movement before the brakes apply you probably need to use this adjusting up method.
- make sure the parking brake is fully released
- Block the steer wheels, then block the mast and tilt forward
- pull the wheels if desired
- adjust up the wheel adjuster behind the wheel while turning it till you feel a drag, then get on the seat and press the brake pedal several times while turning the wheel (this can be done while the truck is running and in drive). This will reset the brake shoes to the drum. Then shut the engine off and go recheck the wheels drag.
You should feel a slight drag on the wheel while turning it if the shoes are properly adjusted.
Repeat this step on both sides.

When you test drive the lift checking the brakes make sure both wheels apply evenly, get running at a semi fast speed and apply the brakes harshly till the wheels slide. It will leave a pattern on the ground/asphalt/concrete and you can note if they are applying evenly or not. If you can find a gritty area or dirty area it will make it easier and will not make you apply them as hard.
Make appropriate adjustments to get them both applying evenly. Do this final adjustment in both directions fwd and rev.

Note: when de-adjusting the brakes you will need a small screwdriver to stick in the adjuster hole and push back the lock tab on the automatic adjuster that locks into the adjusting wheel so it will turn freely. If you force it to turn past the adjusting wheel teeth it will damage the adjuster locking plate and may not 'auto adjust' properly or lock correctly.