I taught OD rebuilding for Volvo cars for a lot of years, and while we
didn't have type A laycocks, all the ODs are very similar. The purpose of
the one way clutch is to prevent the torque of the engine from causing the
cone clutch in the OD from slipping. Look at the size of the cone clutch.
It is what an inch or so wide by eight inches or so in diameter. Figure
out the surface area of that clutch and compare it to the surface area of
the main clutch on the flywheel. The cone clutch is tiny in comparison. If
exposed to the full torque of the engine on acceleration, and without
something else to reinforce it, the cone clutch would spin and slip. To
prevent this, a one way clutch (or sprag clutch in Americaneese) is used to
back up the cone clutch. This allows free movement in one direction but
locks up tight in the other and prevents slip. So when accelerating the one
way clutch takes the torque of the engine, and the cone clutch is not
exposed to abuse.
On deceleration, the one way clutch releases, and the torque of the is
passed directly. The tires generate very little torque and it can be
handled by the cone clutch alone.
this is exactly the same was what happens in an automatic transmission where
you have a series of clutches, brakes and freewheels to engage the various
gears.
On Tue, Jul 27, 2010 at 7:34 PM, Greg Mandas <gmandas@yahoo.com> wrote:
> John,
>
> I just read your article on the overdrive on your site, healey6. Nice site.
> You say the roller clutch allows the OD to drive the rear wheels but not
> the oposite, as it will damage the OD unit.
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