you are correct, and i welcome your comments! i totally agree with your observation, though i think my margins will be OK here. i welcome your ideas though.
actually the lower bolts are single shear, too. the lowers are 5/8" uppers 1/2". all are grade 8. the 1/2" bolts are the limiting item of course.
there's two sets of forces i tried to consider; normal operating and hard curb-whacks, or crashes, eg. "none of the above".
here's my logic: i'll state it as if it's fact, it's easier to write. if you smell a turd, yell! lol
the engine makes 200 ft/lbs torque, in first (3.1) and this axle (2.73) that's some 1700 ft/lbs at the axle. let's say i rev it up and dump the clutch (haven't done that for 40 years!), what with the flywheel and mass, twice that? say 3500 ft/lbs. the distance between the heims is about half a foot, so double again, 7000 lbs of force, best/worse case operating. assuming the tires would grip that much, doubtful.
there's four grade-8 bolts in shear, two are 1/2" so they are the limiting case. from what i read a 1/2" grade 8 bolt has a shear strength of 17,000 lbs. there's four of them, but assuming two are loose/uneven forces/bad geometry, even two of them should have enough margin.
the heim is spaced off the bracket by 1/4" spacer. the angle isn't 90 degrees either.
but i think the ear they are bolted to will deform first, before the bolt fails.
i think i'm talking myself into making them double shear, lol. now's the time.
the "none of the above" crash/curb-whack i think is more a worry. i've seen especially front end parts catastrophically fail "for no reason" that later examination shows a very old (corroded) crack in an arm, etc. i assume from an older crash that was repaired. that's more my worry.
i also have the road experience of a much simpler, weaker, system -- no bolts in shear though -- that was simply two 1.25" DOM .120" wall tubes with a boxed end that clamped to the factory leaf spring perch on the axle tube. that simple system took all the operating torque. i had no way to measure "windup" flex but there was zero static deformation after most of a year of operation.
with a big motor and serious tires and gears i think this system would need a different implementation.
and this is my first time using heims. obviously they work, but i can see how easy it is to mis-use them. eg. my forces are not at 90 degrees (15 deg off) so that adds to the complication... and there's nothing compliant in the system except the tires.
actually the lower bolts are single shear, too. the lowers are 5/8" uppers 1/2". all are grade 8. the 1/2" bolts are the limiting item of course.
there's two sets of forces i tried to consider; normal operating and hard curb-whacks, or crashes, eg. "none of the above".
here's my logic: i'll state it as if it's fact, it's easier to write. if you smell a turd, yell! lol
the engine makes 200 ft/lbs torque, in first (3.1) and this axle (2.73) that's some 1700 ft/lbs at the axle. let's say i rev it up and dump the clutch (haven't done that for 40 years!), what with the flywheel and mass, twice that? say 3500 ft/lbs. the distance between the heims is about half a foot, so double again, 7000 lbs of force, best/worse case operating. assuming the tires would grip that much, doubtful.
there's four grade-8 bolts in shear, two are 1/2" so they are the limiting case. from what i read a 1/2" grade 8 bolt has a shear strength of 17,000 lbs. there's four of them, but assuming two are loose/uneven forces/bad geometry, even two of them should have enough margin.
the heim is spaced off the bracket by 1/4" spacer. the angle isn't 90 degrees either.
but i think the ear they are bolted to will deform first, before the bolt fails.
i think i'm talking myself into making them double shear, lol. now's the time.
the "none of the above" crash/curb-whack i think is more a worry. i've seen especially front end parts catastrophically fail "for no reason" that later examination shows a very old (corroded) crack in an arm, etc. i assume from an older crash that was repaired. that's more my worry.
i also have the road experience of a much simpler, weaker, system -- no bolts in shear though -- that was simply two 1.25" DOM .120" wall tubes with a boxed end that clamped to the factory leaf spring perch on the axle tube. that simple system took all the operating torque. i had no way to measure "windup" flex but there was zero static deformation after most of a year of operation.
with a big motor and serious tires and gears i think this system would need a different implementation.
and this is my first time using heims. obviously they work, but i can see how easy it is to mis-use them. eg. my forces are not at 90 degrees (15 deg off) so that adds to the complication... and there's nothing compliant in the system except the tires.
