Vintage Parts Axle - … And A Beaming Smile Spring Time …

Opinions on the amount of caster an early I-beam frontend should have will always vary, with Posies recommending 6-7 degrees and Fatman Fabrications building 5 degrees into their Vintage Bonz. I’ve always built 6 degrees into my builds, measured here with the kingpin pushed through the axle boss from below.

My careful pre-planning actually worked this time, but a common old-school trick to increase caster has always been to pie-cut the wishbone just behind the yoke and re-weld it at a greater angle. The Fatman ’bones are slid 2 1/2 inches over the yoke before welding, so cutting them to re-weld would involve cutting through solid steel.

While I didn’t use the Posies frame mounts, it would be remiss of me to not show how they are intended to be installed. The gussets are supplied with the mounts, along with the hardware.

I elected to mount my springs above the framehorns, the similar curvature pleasing to the eye, not to mention it offered an extremely low ride height yet still safely above the scrub line. This therefore somewhat dictated where I’d mount my axle.

With both springs clamped in place where they looked best—i.e. where the curvature matched the framehorns—I grabbed an accomplice to ensure they were square with each other and the frame, first by measuring across at the front and rear …

… then by measuring diagonally in both directions. The axle is not in its final location here.

With racer tape on the top of the axle, we established its centerline and measured out from there by half the distance between the springs. Adding 7/8 inch brought our measurement to the center of each spring eye, as the springs are 1 3/4 inches wide. The tape was marked accordingly. Somewhat luckily this put the centerline of our axle perches exactly between two of the holes drilled through the axle. Though it would have been even luckier if it had aligned with one of the holes, as I could have used the Posies perches!

Instead of modifying the Posies frame mounts by adding triangular plates to each side, I elected to make new mounts from a single piece of 1/4-inch wall square tube with an internal width of 2 inches, slightly wider than the spring, and 1/16-inch wider than the Posies mounts. I’ll place large 1/8-inch washers between each side of the spring and tube. I sourced a pair of flange nuts identical to those used by Posies, and reused their hardware.

With my new mounts clamped to the Posies mounts, I used a transfer punch to replicate the spring mount hole positions before drilling them using a Rotobroach in a pillar drill.