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Old 03-12-2013, 09:47 AM   #1
RobboJ OP
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Front hub question

On my R75/6 I replaced the front hub with one in much better condition from a 90s apparently...
The internal diameter is smaller (for the smaller type axle), and I can't seem to work out if it is cast this way or there is some kind of tube inserted into the hub.

Would I be able to remove and replace this with a larger diameter axle so that it fits my forks? I'm running twin disc ATEs.

On the parts fiche it looks like I just take the bearing race out and it should slide out - is this the case? It seems to run from one race to the other.

Can I get a replacement part? If not can I drill it to fit my axle??!!!
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Old 03-12-2013, 01:14 PM   #2
Rob Farmer
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www.realoem.com is useful for reference. The prices are in dollars but give you some indication of what parts are still available. http://realoem.com/bmw/showparts.do?...54&hg=36&fg=05

Im looking at the 75/6 wheels and seeing the same size bearings as the 90s - 40X17X14

Your wheels use taper roller bearings that need to be shimmed correctly. The central tube has a small shim that gives the correct distance between the bearings. it's often called a wedding band. You will need to allow for re shimming the new bearings if you are chopping and changing parts.


Rob Farmer screwed with this post 03-12-2013 at 01:20 PM
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Old 03-12-2013, 04:05 PM   #3
chollo9
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The only possibility I can think of is maybe someone installed #12 in Rob's diagram above, which used to be available for the opposite issue, so you could fit later wheels to earlier bikes. If so, it could be removed.

It's a shot in the dark . . .
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Old 03-12-2013, 04:45 PM   #4
disston
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It sounds to me like you have a 1974 R90S front hub. All the 1974 bikes used a 14mm front axle. I seem to recall that the hub casting itself was different in the axle area and to put the later parts in this hub one would have to bore the hub larger. I'm not sure of this info now because I never had to do this. When I had a 1974 bike I used the 14mm axle and never had a problem with it.

There is info on the Web somewhere about this. Try Mr. Snowbum's site and also Duane Ausherman's site. One of these longer threads has more info on these hubs I think.

http://bmwmotorcycletech.info/

http://w6rec.com/
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Old 03-12-2013, 05:28 PM   #5
chollo9
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Okay, let me rephrase that, "One possibility is that . . ."
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Old 03-13-2013, 12:55 AM   #6
Rob Farmer
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Quote:
Originally Posted by disston View Post
It sounds to me like you have a 1974 R90S front hub. All the 1974 bikes used a 14mm front axle.
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Old 03-13-2013, 03:09 AM   #7
RobboJ OP
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Thanks for the help, will investigate at the weekend
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Old 03-13-2013, 08:54 AM   #8
Big Bamboo
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Yep the earlier hub has ridges inside the bore to hold the bearings spacers centered. You will need to machine these down for the wider outer spacer tube to fit. The info is somewhere on Duanes website.
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