4LS to Roadholder Fork (part 1)

My friend JW is building a traditional British cafe racer from parts he’s been collecting for some time. He has a Norton slimline featherbed frame, a Roadholder fork, and Ariel pre-unit motor and a beautiful hand-shaped aluminum tank. He suggested that documenting the conversion of a Suzuki 4LS brake (four leading shoe) to an early Brit fork might make for a good read. I agree. Let’s do it!

This hub and brake setup is pretty sought-after for its significant stopping power and that it’s not a modern disk. I think they’re worth upwards of a grand, so I’m measuring three times for every cut. Modification is necessary because this hub is over and inch-and-a-half wider than the forks it’s going be used with.

My plan is to remove material from both the brake plate axle supports and the inside fork bosses to make it fit. The original brake stay boss needs to be removed from the fork leg and straps will have to be made to anchor the brake plates to the fender mount bosses on the fork legs. The speedo drive mechanism and associated features on the brake plate will have to be removed and welded in. A new axle will also have to be made once I get the hub fitted up nicely. I’ve decided to no attempt any lightening of this brake/hub (it’s HEAVY) as I don’t really see any opportunity for significant lightening. The internal aluminum webbing could be drilled but how much weight would a few slugs of aluminum save when compared to the four thick iron liners and various steel linkage parts? Not worth it to me. For now, JW agrees. But he’s one to tinker (and do it well) so we’ll see what he does with it after I give it back to him.

First order of business last night was to measure the fork and hub to get the final numbers for use in trimming down this hub.

Using layout dye on my metal bench top to measure the width of the fork at the bosses.

Using a square to ensure leg bosses are perpendicular to the table surface. I then scribed the table at the back of the square on each side and measured the distance between the marks.

The final numbers tell the tale. Having a metal bench top is great for notes and measurements.

Indicating the fork leg on the Bridgeport. I can remove less material from the brake plate axle support area by taking some material off the forks.

Milling the fork leg. I removed .160" from each leg.

Fork leg done. Looks nice and clean.

Casey generously offered to polish up all the aluminum parts. He also dressed up the brake liners. Nice work, Casey.

The pile. The fork internals are pretty crusty. Nothing a week-long soak in the parts washer and some wire brushing won't fix.

No wonder this thing's so heavy.

You can see the speedo drive mechanism on the left brake plate. This will have to be removed. Someone has already attempted to lighten the webbing in the hub and done a questionable job of it.

Next installment will be figuring out how to mount the brake plates the milling machine table and removal of the speedo drive parts.


7 thoughts on “4LS to Roadholder Fork (part 1)

  1. Wow another nice project underway. That brake will look and work well on those forks. Keep us posted on the progress. Which engine is he going to use ? A single or twin?

  2. you guys have way too much fun in the shop,tuesday nights are tough for me to make it up to spend some quality time…..hollar next time youse are down there on the weekend making chips and playing on the mill,love ripping shit up.
    Say Hey to Casey ,Dan and VSL

    Great seeing you again,gotta do it more often

    • Thanks, Sal. Keeping busy. Not much time for profiling these days and I’ve got holes in my Vans. No cuts or patches, though. When you coming around? On the other hand I WILL get up your way this season.

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