Put it in neutral let the clutch out, rev it slightly let it idle back down, then push in the clutch, wait a couple of seconds, then try reverse. If it won't go in, or grinds the clutch is either out of adjustment, or the pressure plate is getting weak.
Does this happen in all gears? If it does, it is most likely in the clutch, or the hydraulics of the clutch.
If it only catches in one gear, I would try Redline synthetic oil until you have time to rebuild trans. Joe
I'm having a similar problem with my 78 however it seems to slip only when I try to go through the gears fairly fast. I've simply concluded that my clutch is going bad and that it's time to change it. I'm I correct in assuming that it's going bad or should I start looking into other possibilities? If the clutch is bad, can anyone recommend a good brand?
I think your slave cylinder is on it's last leg if you need to pump the clutch. Start from there, if you do not have any slipping. Take the cylinder out, 2 bolts plus hyd. line. Bolt new one in, bleed the system and you are back in business.