I just checked out the front brake drums on my BN2. Set a drum up in my
lathe & measured with a dial indicator. After chucking on the center
hole, & zeroing there, measured the total indicated runout (tir) at the
flange inner surface & the inside shoe surface at .008". The outside
drum surface measured the same runout. Drum wall thickness varied from
.300" to .296". I think .004" off center in the casting is pretty good
for 48 year old drums. Don't know why the runout was between the center
hole & the rest of the drum. But then I don't know the machining
sequence that was used. The other front drum was nearly as good with
.009" tir. No taper (bellmouth) & no egg shape as measured with an
inside micrometer. Didn't bother to check the rear drums. Drum id's were
11.005". Don't know if this is standard. Have never had any vibration
problems, & have never checked balance. Was just curious. I think this
proves that the factory could get it pretty close, at least in 1956.
Maybe they got sloppy later on. Or maybe just lucky sometimes.
I would be interested in what others find if they try the same measurements.
Dave Russell
BN2
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