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Discussion Starter · #1 ·
Right..i'm getting pissed off with this now!

So, I got a rear caliper off a 1200 sportster to use on my build.. meaning I would need to get a new, bigger, brake disc.

Measured the front disc I had, was just the right size. 11.8cm from edge of hub - perfect!

bought a front one off ebay... when it arrived the bolt holes are too small and wont take the bolts my rear hub has! further to that, its the wrong side as the shapes on the disc flow backwards, instead of forward, if that makes any sense...

thought, bollocks to it, I'll get another disc.

Off to eBay. Found one off a 1980 sportster, perfect I thought! its the rear and all...
arrived today... bolts are perfect size... hub hole size, is too fkin small!!!

On the left is the rear one I bought, on the right the front one



questions.... from what bike do I need a rear brake disc? any ideas?

the hub hole should be - 5.6cm - 2 1/4
the distance from hub edge to disc edge should be - 12cm - 4 3/4(or around that)
and the holes for the bolts are - 1cm

Sorry, I'm not used to the metric system, and google is not a very good converter!

or can i just get the hole, on that rear disc I got, machined and made bigger to fit my hub?

its driving me nuts trying to find a disc that will suit the hub size, the bolts size and the caliper!
 

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"Generally" speaking.....as there are always exceptions to every rule. Harley-Davidson rotors are separated into two distinct groups. Those that are designed wheels with sealed bearings and those rotors for wheels with tapered Timken style bearings. The sealed bearing rotor have a larger center register (about 2.25") while the Timken bearinged hubs have a smaller center (~2"). The other major difference(s) is the the size of the mounting hardware. Fronts use a 5/16' bolt/screw and rear use 3/8". BTW...those are two rear rotors in your picture. 1 "early" on the left, and 1 "late' (2000+) on the right. FWIW, rotor ODs were 11.5" until 2008 when they went to 11.8"
 

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Discussion Starter · #4 ·
ho no....now you have confused me even more then!

they are both rear??
but the holes on the one on the right are smaller, and fit perfectly on my front rim...
Right, I'm going in the garage and take a couple of pics as this is really confusing me...
 

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I apologize.........From my angle the holes looked alike. As I stated, front rotors and wheels use 5/16" hardware and rears use 3/8" bolts for securing the disc to the wheel. The disc on the left is an early Evo rear rotor using countersunk allen bolts.
 

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Discussion Starter · #6 ·
right, just took this pic..

top left - front hub / top right - left hub
bottom left - front hub bolt / bottom right - rear hub bolt

I have a 16" on the back and a 19" on the front



I have also just noticed that the left disc I have (rear) is thicker than the front one, which when i tried on the hub it fitted perfectly over the lip... so I guess even if I get someone to machine the hole of the rear one to make it bigger to fit the hub, then there will be a bit sticking out the lip on the hub.. would this be a problem?

ideally I would just like to get a disc that matches the rear hub, but I dont have a clue which model bike its off...
 

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You're right, there is another group of Harley rotors, too. Up front the '77-'83 dual disc FX's, Sportys, and FXR Shovels, and the '79-'83 FLH's front and rear use rotors with a 2 3/8" dia. center hole.

"Generally" speaking.....as there are always exceptions to every rule. Harley-Davidson rotors are separated into two distinct groups. Those that are designed wheels with sealed bearings and those rotors for wheels with tapered Timken style bearings. The sealed bearing rotor have a larger center register (about 2.25") while the Timken bearinged hubs have a smaller center (~2"). The other major difference(s) is the the size of the mounting hardware. Fronts use a 5/16' bolt/screw and rear use 3/8". BTW...those are two rear rotors in your picture. 1 "early" on the left, and 1 "late' (2000+) on the right. FWIW, rotor ODs were 11.5" until 2008 when they went to 11.8"
 

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Discussion Starter · #8 ·
ho great! now there's even more variations! lol

I'll never get out of this mess!! So early evo rear bolts are counter-sunk? If I can get hold of some, which I dont seem to find anywhere, then if I get the hub hole machined all should be good no?
 

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Get some thick soled shoes, or a anchor. Both are unifit. Sorry for the humor, I feel your pain.
 

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Practical help: What's needed is a rotor from the rear of a 2000 or newer Sportster. A rear rotor from a Dyna or Softail of the same years will work, but the shapes on the rotors will flow like the front one you already have.

You could bore the hole in the center of the 1980 rotor to fit your hub, but you'll have to deal with those countersunk bolts which are a serious pain to get back out after they've been in there a couple years or so. You can get the stock style bolts, like in post 6, in chrome if you like.
 

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Discussion Starter · #12 ·
well, dealing with the countersunk bolts won't be a major worry as I have ways to get tough bolts out...

the problem is I can't even find countersunk bolts! remember...I'm in England, so getting parts here is not as easy as for you guys over the pond...
Can I just fit the stock bolts to the disc? it has a lip on it as it goes in, so the standard bolt can rest on it, doesnt need to be countersunk?
 

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Discussion Starter · #13 ·
yeh, loads of room, i took this pic few days ago, the disc on it is the front one, just against the hub as I couldnt bolt it down due to bolts not fitting the hub.

I'll just get the disc bored out then and see how it goes....

 

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Discussion Starter · #14 ·
right.. just left the disc at the engineering place to get it bored out, will be ready by the end of the day.
 

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Discussion Starter · #15 ·
This is really not going very well!!! arrrrgghhhhhhhhhhhhhhhhhhhhhhhhhhh

So, got the disc from the eng place, perfectly bored out. when I pick it up the guy says... "btw, when we put it on the machine, its not spinning straight, it might be warped..."

Ho fkin great!!

Got home, got it in place, wheel on the axle, spin the wheel.... the disc is all over the fkin place!!!
what a waste of time and money!!

on a good note, contacted the eBay seller, told him the disc he sold as very good condition was fked.. he apologised and refunded the money and said no point sending it back.

ho well... on the hunt for a rear disc again!
 

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Damn, the machienest should have stoped and called before he bored out the hole. Some builds are just like that, ya fight them all the way through, hang in there, ya'll get it.
 

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Discussion Starter · #17 ·
to be honest its not a proper engineering shop, they do hydraulic rams and their lathe is the size of a transit van lol.. still he could have called. there isnt any proper engineering shops here in Newbury and these guys had done some bits for my land rover before....

but anyway, its all part of the build, going back and forwards and struggling with bits, learning, head scratching, etc... its all gonna be worth it once its working and running!
 
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