I looked in the parts book and it calls for a 9/16-12 x 3-3/8 with no grade specified. 90 to 100 lbs. may be too much torque for the application, but the bolt shouldn't have broken off because that is about normal for a grade 5 bolt. 3-3/8" length is a special bolt. I wonder if someone didn't put in a 3 1/2" and it bottomed. Or the last person to have it apart had an impact and grossly over tightened it. We have this happen quite often. Then when you turn them the other way, they break. All I have messed with in the last 30 years is rears for semis. They use grade 8 bolts for the bearing caps. I don't think a grade 8 would hurt on a 3/4 ton.
