This article is from the alt.usage.english FAQ, by Mark Israel misrael@scripps.edu with numerous contributions by others.
Robert L. Chapman's "New Dictionary of American Slang" (Harper &
Row, 1987, ISBN 0-06-181157-2) says: "hell-for-leather or hell-
bent-for-leather adv "from late 1800s British" Rapidly and
energetically; =all out, flat out. "You're heading hell-for-leather
to a crack-up" [origin unknown; perhaps related to British dialect
phrases "go hell for ladder, hell falladerly, hell faleero", and
remaining mysterious even if so, although the "leather" would then
be a very probable case of folk etymology with a vague sense of the
"leather" involved in horse trappings.]"
 
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