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  1. #1
    SnakeAndSkull
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    Default 35mm twin disc forks with 21" wheel - spokes hit brake caliper

    Sup playas, first time posting so yell at me if I'm doing this wrong.

    I bought a nice 35mm twin disc front end with a hub - I had it laced to a 21" rim and ran it without brakes for a while.
    Went to put the discs and calipers on and realised the spokes are brushing past the calipers.

    I'm assuming because the rim is bigger than stock it's changed the angle of the spokes and that's why I've lost the clearance.

    Have I f'd this completely or is there a solution? (besides re-lacing the hub to 19")
    I've scoured the forums as best i can - the subject has been brought up but I've found no answers.

    I swear i see 35mm forks with 21" wheels and twin discs all the time... what gives?

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    The problem is a common one. One solution is to machine the inside of each caliper for clearance. On the '78 style single piston H-D caliper, it's pretty easy. Cut at an angle, similar to the way the caliper is cast, and remove the minimum necessary for clearance. You will weaken the caliper by doing this, and that might result in some caliper flex under pressure. There is risk involved.

    I recently tried to do this same machining to a '00 style four piston H-D caliper, but I struck brake fluid before I got enough clearance for a 21" wire wheel. One of those experiments that did not go well.

    Jim

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    You can also space the rotors out just a little. In fact, Harley used thin (like .040") spacers on some of the models (41814-76.) Here's my '78 FXS with a stock narrow glide hub and a 21. It was a long time ago, maybe 1987, but I think that's how i solved the problem.

    Click image for larger version. 

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    One more thing.

    35mm narrowglide hubs are 4.5” wide

    39mm narrowglide hubs are 5.5” wide.

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    I recently tried to do this same machining to a '00 style four piston H-D caliper, but I struck brake fluid before I got enough clearance for a 21" wire wheel. One of those experiments that did not go well.
    What rotor OD did you use? The larger later rotors are easy to bore for the larger early hub pilots.

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    Quote Originally Posted by farmall View Post
    What rotor OD did you use? The larger later rotors are easy to bore for the larger early hub pilots.
    This was a 39mm single disc front end with the normal 11 1/2" rotor. I just put the 19" wheel back on it. Experiment gone bad.

    Jim

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    Quote Originally Posted by Salty View Post
    One more thing.

    35mm narrowglide hubs are 4.5” wide

    39mm narrowglide hubs are 5.5” wide.
    Not necessarily. Depends on the year/model. Most hubs that came with 39mm front ends are the same width as the earlier narrow glide hubs.

    Jim

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    As MOTher noted above:

    Disc Rotor Spacer
    ".040" thick spacer is used to re-establish correct rotor-to-caliper alignment and spacing when ever servicing wheels, brake calipers, supports or rotors on Original Equipment disc brake systems from 1973 thru 1984." $7.00
    Click image for larger version. 

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    http://www.cas4.com/brakes/brake-hardware-spacers.html

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    Will add, that I did some business many years ago with a local chop builder and he was running a Springer. He didnt notice it until I pointed it out but he had ground down half way thru his spokes, the reason is at rest they cleared, But on full compression the rocker bolts swung down and rubbed on the spokes, He was lucky I caught it, scared the crap out of him as he rode a lot at high speed on freeways.

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    Quote Originally Posted by JBinNC View Post
    Not necessarily. Depends on the year/model. Most hubs that came with 39mm front ends are the same width as the earlier narrow glide hubs.

    Jim
    Sir, you can believe what you want, but hub width widened when the bike came stock with the newer 39mm.

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    Quote Originally Posted by Salty View Post
    Sir, you can believe what you want, but hub width widened when the bike came stock with the newer 39mm.
    I don't have to believe it, I know it. I've got one sitting right in front of me. Go learn something, jr.

    Jim

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    On hub widths. I worked the parts counter at a couple HD dealerships in the first decade of this century. Once, just for the heck of it I went through all the parts books and found 11 different part numbers for narrow glide disc brake hubs. I'm sure there are more now. Some were unique, like the '73 only hub for a 10" rotor and banana caliper. Some were just different finishes. The factory 21" hubs are different in that they have staggered spoke holes.

    I just went out and measured a few hubs I had; '73 as mentioned above, '74-'77 for the cloverleaf rotor and pie slice caliper, pre 2000 21", and a post 2000 single disc for a 19. They were all the same width at the spoke flange except the newest one which was about 1/4" narrower. The later 2 were wider where the rotor mounted. I guess how wide it it depends on whether you're measuring at the axle, the rotor flanges, or the spoke flanges.

    All the 39 mm trees I have are 4 mm wider, center to center, than all the 35 mm trees I have, making them the same distance between the inside edge of the fork tubes.

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