1964 Series IIA 109 Clutch Issue

Was it not working before???
If it was working what did you change?
If it wasn’t working replace the MC

Typically when the slave cylinder goes, the master cylinder is bad or close.
This is the best option to you:
Dorman Clutch Master Cylinder Conversion Kit - Mechanical

I don’t think that will work with the early 2A trucks unless he’s converted to a later brake tower.

Know the early IIA had that silly reservoir can that fed fluid to both the clutch and brake master cylinders.
If you are not hell bent original, post 3 is the way to go.
Think the Doorman cylinder does fit the early petal box, but have been wrong before on some things..

While the clutch is a nice feature, it's not too difficult to shift the gears without using it . Can you shift with the engine off and have it go Ito gear? If that's the case it's probable that your master has also pooped out. I highly recommend keeping it as original as possible as altering the clutch will knock off several thousand of the truck's value.
Replace all of it. Master, hoses, included. If needed, you can get the original master sleeved so it can remain as original (if it is the original)

Yes, the clutch was going out and i replaced it with an LOF clutch. I can shift all gears when it is off but can’t get into gear when it is on.

My 65 SIIA 88 had a problem where the clutch would stick to the flywheel if left too long. Hard driving and it would pop loose. (Brake and engine until it frees itself.)
It would also stick after any wading in water, and the left overnight to dry off, I think the plug was missing on the bell housing.

it’s funny the things you just deal with on a LR.

Also years later I replaced the clutch , backward, and it won’t release if in backwards…. So lesson learned.

Did it work right after replacement?

Another option is the possibility the new slave cylinder was bad out of the box.