Shovelhead Trike/Go Kart Axle

Richard D

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I have a Harley Davidson Shovelhead with a rough welded on hardtail. Tuesday I got my fiberglass trike body, made from the original molds from over fifty years ago. Had some wheels custom made.
Himsl Shovel Trike Mockup.jpeg
I ordered my axle with advice I got in this thread:
Got a lot of work to do, figured you guys would be interested since I am using some go kart parts in this project.
 

Richard D

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This will not be driven on the highway. Just cruising around the neighborhood and at shows. I imagine the axle will be short-lived, I will upgrade later to a DNA axle designed for full size motorcycles, but they are $2K and I need this thing to be at least a roller for a while. I will build the rear frame in such a way it won't be too difficult to modify for a heavier rear axle later.
 

Richard D

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Started mocking up my differential. This is a Mazda diff with Polaris RZR brakes.

Early mockup in rear frame:
Himsl Shovel Trike Axle Mockup 001.jpeg

Diff with bearings and modified frame mounting plates. Looks kinda like a fish, huh? I had to cut and bend the top tubes of the rear hardtail frame section so the fiberglass body would sit flush. The top of the rear "fin" will go under that cut for re-enforcement.
Himsl Shovel Trike Axle Mockup 002.jpeg
Also will be making plates to adapt the brakes to the output shafts:
Himsl Shovel Trike Axle Mockup 003.jpeg
The width is perfect to fit inside the Harley frame. The calipers even line up perfectly. I thought I would need to fabricate a complete rear frame.
Himsl Shovel Trike Axle Mockup 004.jpeg
I will do some some more CAD revisions and then have these plywood parts waterjet cut out of 3/8" steel plate.

There will also be two more "outrigger" frame rails on either side, attached to the seat tube near the inboard frame rails, with outboard bearings to support the wheels.
 

Denny

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I think you have a solid plan that should work as you expect! The only thing I would add is another bar or crossmember to the backside to keep the rear plates from flexing and cracking. But it looks like you did your homework!
 

Denny

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With fresh eyes and brain fully engaged you may want to rethink your brakes. If you had a front brake your system probably would have worked. But since you don’t, and you don’t have a posi carrier you might want to put brakes on each axle side. With only one brake on the carrier is not enough stopping power for about 600 lbs plus rider even at low speeds. Plus you will only have really effective braking on 1 wheel. Meaning when you go to stop it will try to spin around on you. All not good if a kid steps out in front of you. With the IRS you are going to have it will be aggravated even more. But if you put a brake on each side it will help you to stop straight and in a controlled manner. All the while shortening the stopping distance. Also I would also fill the differential with John Deere corn head grease. It pumps in like regular grease and when not moving it is solid like grease. But when it is moving it has the consistency of a thick oil. Allowing better lubrication of the spider gears and cross bars. It really is some neat stuff, been using it for years on my cars with manual steering boxes. No problems and even steers easier in cold weather.
 

Denny

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With fresh eyes and brain fully engaged you may want to rethink your brakes. If you had a front brake your system probably would have worked. But since you don’t, and you don’t have a posi carrier you might want to put brakes on each axle side. With only one brake on the carrier is not enough stopping power for about 600 lbs plus rider even at low speeds. Plus you will only have really effective braking on 1 wheel. Meaning when you go to stop it will try to spin around on you. All not good if a kid steps out in front of you. With the IRS you are going to have it will be aggravated even more. But if you put a brake on each side it will help you to stop straight and in a controlled manner. All the while shortening the stopping distance. Also I would also fill the differential with John Deere corn head grease. It pumps in like regular grease and when not moving it is solid like grease. But when it is moving it has the consistency of a thick oil. Allowing better lubrication of the spider gears and cross bars. It really is some neat stuff, been using it for years on my cars with manual steering.
 

Richard D

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I will have brakes on both sides, I just didn't have the other mocked up. The RZRs weigh over 1000 lbs, so I'm hoping the dual discs will be enough. It will not be IRS as such, no springs, and thanks for the tip on the John Deere grease.
 

Richard D

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I am planning to mount the jack shaft on slotted holes for adjustment and use a serpentine belt tensioner on the final drive chain. Some HDs had a nylon "slipper" for primary chain tension so I'm thinking it will be O.K. If not I'll go back with a spring loaded sprocket tensioner. I have seen them pre-fabbed but I bet I can make one as good or better.
 

Richard D

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Some progress:
Custom sprocket from Rebel Gears. There will be an aluminum housing for grease. I will try the John Deere stuff.
Trike Sprocket.jpg
You can see the tabs for the left side brake caliper.
Trike Sprocket & Jack Shaft.jpg
Will have quite a bit of rake. Not sure how much trail is a factor in trikes. If it don't work, I'll cut it off and do it again.
Trike Profile.jpg
 
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