Thread: Rear hub bolts
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Old 02-20-2020, 09:01 AM   #2
Joe K
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Default Re: Rear hub bolts

1) Taper between A-B IS part of the swedging process. But only the outer fraction of the ramp A-B. After swedging the top part A of the ramp still exists, but the bottom part B has been pushed down and "out."

You can get a sense of where this cut occurs by looking at the ID of a new swedge tool and comparing it to the ramp. Keep in mind that swedge tools wear, and this diameter will change with wear.

2) Shoulder CAN be squared off, but one is advised not to as one creates a stress concentration point for lines of force, and this can become a potential crack. Better would be a radius, or maintain the taper.

3) Guessing here (I have not used CI bolts on pressed drums) but based on what I know the reduction should be "overall". (i.e. the whole A-B taper portion)

4) In C dimension, you mean for pressed drums - see reply above. The vendor of CI drums (Mel Gross among others) will probably be able to tell you what he likes to see as he does this regularly - and he has to filter out the potential errors including bolts made wrong, the drums inconsistent thickness, the hubs inconsistent thickness, something a burr or chip in the interstice between bolt and hub, warped hubs.

One might take the thought of the thickness of the bolt circle on a cast iron drum and comparing it to the thickness of the same spot on a pressed steel drum. The difference is how much you should reduce the shoulder A-B height (i.e. irrespective of dimension C)

I think given a pressed drum and a bolt, one would probably learn on the first try if too much or too little metal has been left. You want to buy bolts enough for at least a couple of re-do - consider the cost part of your "learning curve." And one bolt is only 1/5th of the 2/5 bolts needed to actually hold a wheel in place so if its not perfect you go onto the next one and change your setup/machining.

And - when you come right down to it, the swedging ONLY holds the drum in place long enough to get the wheel on and the lug-nuts tightened. Well, this once you get the brake drum surface "trued up" and centered.

As to the ramped portion and the nut/threading action - the ramp could be removed entirely as it has nothing to do with the bolting action.

Of course "back in the day" nobody swedged the bolts - instead they were tack welded in place! (Not recommended.)

Joe K
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Last edited by Joe K; 02-20-2020 at 09:08 AM.
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