Rear drum sizes

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steve
Posts: 60
Joined: Fri May 05, 2006 2:25 pm
Location: Ipswich

Rear drum sizes

Post by steve » Mon Sep 11, 2017 5:08 pm

Hello all

I have a Sportster iron head rear hub and I am wanting a smaller drum and and less teeth on the rear sprocket.
I think I heard once that a Triumph pre unit drum will bolt up to a Sportster hub. Apparently these are a 7 inch drum and the sprocket will bolt on.
Has anyone done this?
If not does anyone have a Triumph 7 inch drum witha bolt on sprocket sitting around that you can take some measurements from.
I need the center hole size and the PCD of the eight mounting holes.

Any other suggestions for a smaller drum on a Sportster hub would be appreciated.

Thanks

Steve

TriNortchopz
Posts: 12
Joined: Sat Feb 24, 2018 5:41 pm
Location: Haines Junction,Yukon, Canada
Interests: Choppers, nature, learning more about choppers

Re: Rear drum sizes

Post by TriNortchopz » Thu Mar 01, 2018 12:25 am

Short of going out and measuring one of mine, here is some info which may be helpful:

Can you identify this mystery brake drum?

It was found in a pile of K parts. The bolt holes match up with a K rear hub. The 46 tooth sprocket (odd) is non-removable (even odder) - it is part of the drum casting.

Is it 8 inch? If not, it is a Triumph rear drum...

The drum diameter is only 7 inches.
It must be coincidence that the bolt hole pattern is the same as a K/XL, and that's how it ended up in a K pile...


http://www.harleykmodel.com/phpBB3/view ... c26b72b983

steve
Posts: 60
Joined: Fri May 05, 2006 2:25 pm
Location: Ipswich

Re: Rear drum sizes

Post by steve » Thu Mar 01, 2018 5:55 pm

Hello I am the original poster of the question. What I have found out is that the triumph and Sportster bolt holes line up exactly and are exactly the same diameter. The center hole on the Triumph drum is larger than the Harley one. A quick measure with a set of calipers shows me the Triumph center hole 56.62 mm and the Harley center hole is 52.9 mm. I purchased a 46 tooth Triumph drum and turned up a spacer to center it on the Harley hub Please note I used a micrometer when I made my spacer so the above measurement may be out by .5 of a mm at the most. The triumph also has a 45 degree chamfer on the hole where it sits on the bub to locate it. I recreated this on my spacer. The drum is around 178 mm. I found Triumph made these in one piece and drum plus sprocket depending on the model. They also commonly came in 47 tooth configuration. I hope this helps.

Steve

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