I'm using modern billet adapters on my SBP drums to run BBP wheels. Car developed a vibration and this is what I found on left front. 3 of the 5 lug studs had sheared off. Nuts on sheared lugs do no appear to have backed off prior to failing. Because I could not buy LH thread lug nuts with the larger conical seat I used the stock nuts to hold the adapter on. Was my error in not using the large conical nuts, or failing to use lock tite on the stock nuts I used, or improper torque on nuts holding spacer to drum. Any similiar experiences ? Opinions ?
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For the naysayers, there is NOTHING WRONG with using spacer/adaptors that bolt on like that. They is literally no difference between using those and using a wheel that has a backspace that places the center of the wheel in the same spot as with the adaptors. None. If the centerline of the wheel is in the same spot, the lever arm on the studs is the same, and the forces to the studs will be the same. As long as the studs/nuts have the proper thread engagement and proper torque there should be no issues. You do of course have 2 sets of lugs to torque and
maintain torque on.
As for why they failed, I will say it is likely a combination of several of the things you mentioned.
-The nuts were over torqued
-How often did you check/retorque the nuts (all of them)?
-The studs are 50+ years old and unknown history. Could have been over torqued dozens of times previously
-The adaptors were likely designed for a 1/2" stud, you're using 7/16", so the fit at the studs might not have been sufficient
-The smaller nuts may have less surface area engagement on the adaptors, so, the clamp force might not have been sufficient between the nut and stud
And finally, is the angle on the original conical nuts the same as the later ones? Because if the angle on the nut doesn't match the adaptor you might not have had the proper interface.
There is no issue with using the adaptors, BUT, you must properly torque the nuts and re-check them at the appropriate intervals. And the studs do need to be in good condition. Personally, I would not use adaptors with stock studs of unknown history. Because really, using the stock studs on a 50+ year old car is a crapshoot to begin with. Yes, lots of people do it. And if you don't drive a ton, use factory wheel sizes etc then it may never be an issue. Start driving more, running wider or heavier wheel set ups etc and especially with the 7/16" SBP studs you can definitely be pushing your luck.
