German torque. Gutentite.

 

Or thighten it til it starts to loosen, then back it off a 1/4 turn

 

Read the link below, grade 8 is ALWAYS better than grade 5. However, the engineers at the auto companies build to a specified strength, no more as any extra would cost more (even a few pennies adds up over thousands of vehicles).
ROCKCRAWLER.com - Grade 5 vs. Grade 8 Fasteners

If you're torquing a 1/2-13 grade 8 bolt to 150 foot lbs, its likely overtightened and failing because of that. I have a print out of the chart in the following link and have used it without and problem so far. Note the difference between plain, plated, and waxed (oiled?) bolts.
Proper Bolt Torque - by Zero Fasteners

 

Great Article tecgod, it explains a lot in a short article.

 

Thanks, I think I saw it linked from here somewhere.... might have been the offroad or garage forum though. Education is always a good thing