Outdoor Power Equipment (Lawn Mowers, Snow Blowers, Chain Saws and more) Discussions

my old  1980 Yardman let me down  while clearing  or so inches after work today.    It  started after about   6-10  pulls   it would sputter and black smoke would come out the muffler.   Anyway  it finally started and I i warmed it up and started to clear the drive   I made the first pass and punched through the EOD.  I turned the blower and put it in reverse.... Nothing!  it wouldnt move.  I tried all 5 forward speeds ans both reverse   but the wheels didnt move one bit.    Motor was running fine and augers were moving.  it was too dark to work on it tonight  .I ended up using my 4.5hp single stage to finish the job.   So what do you all think caused this sudden drive failure?  I will work on it this weekend   .What should I be checking. ?

FYI for those who dont know   this is a 5hp 1980 yarman  two stage blower.