| engineering behind choosing fastener (bolt) sizes [message #167921] |
Sun, 29 April 2012 06:36  |
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RF_Burns
Messages: 2277
Registered: June 2008
Location: S. Ontario, Canada
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I just finished changing to rear disk brakes and made this observation.
The rims are held on by 8 big b'jezus 1/2" fine thread bolts on about an 8" diameter. Makes sense, lots of weight on them.
But the whole wheel and brake assembly is fastened with 4 little coarse thread 3/8" bolts set no more than about 3" apart (very little mechanical advantage). Mind you they are grade 8 bolts and you could argue that after 35years the corrosion between the spindle and the bogie arm does most of the "fastening".
Same thing on the one-ton front end. The bearing assembly in that case is fastened with just 4 bolts on a much smaller diameter (however about 1/2", most likely metric equivalent).
So if four little 3/8" bolts on a 3-4" diameter can hold the whole wheel assembly safely, why is eight large bolts on a larger diameter needed to hold the rim and tire only?
Inquiring minds want to know!
Bruce Hislop
ON Canada
77PB, 455 Dick P. rebuilt, DynamicEFI EBL EFI & ESC.
1 ton front end
http://www.gmcmhphotos.com/photos/showphoto.php?photo=29001
My Staff says I never listen to them, or something like that
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