What was wrong with Joe? *spoiler*

I believe you are referring to Joe Harley,William Harley's brother. Because he was in a VA hospital, and died there in 1956, I just assumed it was because of some injury related to military service. The series touches on that when Joe influences little brother to build motorcycles for the military during WWI. Harley was initially against the idea of profiting from war, perhaps because of his brother's condition. I can't tell you whether what is depicted in the movie is factual or not, only that Joseph W. Harley was born in 1870 and died in a VA hospital in Illinois in 1956.