If the transmission is working OK in reverse, then the front pump is building hydraulic pressure and the problem is not likely to be low fluid level, restricted filter, or any other easy to correct condition.
Because you have lost forward gears (or at least first gear) you have probably got either a broken band or damage to some other held component used in first gear operation. The transmission is going to need to be removed and disassembled for overhaul to correct this particular problem. There are no electronic components to fail on a 1976 model transmission; all failure parts are internal.
Although I am sure this is not what you want to hear, If it is helpful an accept would be most appreciated! Thanks!
