Why 1929 to early-1932 steel friction discs are not
interchangeable with later-1932 to 1940 steel friction discs:
In 1931, the outer clutch disc was redesigned for the DLD model only,
requiring the steel friction disc to be redesigned to match. The
change was incorporated into all 45” twin models by mid-1932.
Steel friction disc #2535-29 is used on later 1929 to 1934
singles and later 1929 to early 1932 Standard 45" twins.
Looking at the photo below we notice that the sides of
the splines in the disc are parallel and the sides of
the splineways converge toward the center of the disc.
Steel friction disc #2535-31 is used on 1931 DLD,
later 1932 to 1940 standard 45" twins and 1932 to
1934 C singles. Looking at the photos below we
notice that the sides of the splines of the
disc converge to a point near the center of
the disc, and the sides of the splineways
When we compare the shape of the splines,
the difference becomes apparent.
If we try to fit an early friction disc
over a later outer disc, we find that
there is too much play and the friction
disc(s) will pound against the splines
of the outer disc.
If we try to fit a later friction disc over
an early outer disc, we discover that it
just won’t fit.