Advice about uphanger fitting

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robjordan
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Advice about uphanger fitting

Postby robjordan » 17 May 2014, 8:15pm

I bought a Tektro uphanger [http://tinyurl.com/ltp9vzt] with the intention of fitting to my new Bob Jackson World Tour. It turned out to be a bad choice. On my threaded forks, the headset bottom protrudes a long way from the fork crown. I considered trying to make it fit with spacers, but on the Tekro uphanger, the rear face which is meant to attach to the fork is shaped to mate with a curved fork crown.

So I'm considering an alternative e.g. this one http://tinyurl.com/n3h5855 by Raleigh. It will still need a spacer or two to stand clear of the headset. I'm a bit concerned about the mechanical stability though, because the height of spacers would seem to provide leverage for the bolt to shear on the fixing hole, especially as the BJ forks have threaded mountings front and rear, rather than a bolt passing right through the fork from front-to-back.

Am I being too cautious? Do you think it will hold if I just bolt it into the threaded front mounting hole?

Photo to make this clearer:
https://www.flickr.com/photos/64768841@N00/14184075636

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gaz
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Re: Advice about uphanger fitting

Postby gaz » 17 May 2014, 9:28pm

I'm wondering what problem you are trying to solve with an uphanger.

I think the standard uphanger bolt is M5 and suspect the fork crown threading to be M4, which may complicate matters further.

Just to add that I have a Bob Jackson World Tour (albeit an older model with no drilling on the fork crown) and my Claud Butler has an uphanger very much like the Tektro.
2020 : To redundancy ... and beyond!

robjordan
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Re: Advice about uphanger fitting

Postby robjordan » 17 May 2014, 10:53pm

gaz wrote:I'm wondering what problem you are trying to solve with an uphanger.

Judder. And awkward cable routing, up and over the bars to reach a stem-mounted hanger.

gaz wrote:I think the standard uphanger bolt is M5 and suspect the fork crown threading to be M4, which may complicate matters further.

Good point, that might be a further problem.

Rob

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gaz
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Re: Advice about uphanger fitting

Postby gaz » 17 May 2014, 11:09pm

I'm surprised you can't route under the bars but then again I couldn't manage that on my Claud, hence the uphanger.

My Jackson has a somewhat chunkier and presumably less flexible headset hanger from back in the day when such things weren't so hard to find.

DSCN0203.JPG
Dia Compe 1" Hanger
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MikewsMITH2
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Re: Advice about uphanger fitting

Postby MikewsMITH2 » 17 May 2014, 11:12pm

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cjchambers
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Re: Advice about uphanger fitting

Postby cjchambers » 17 May 2014, 11:52pm

robjordan wrote:Judder. And awkward cable routing, up and over the bars to reach a stem-mounted hanger.

http://www.sjscycles.co.uk/dia-compe-12 ... tomsection

This one (beautiful, incidentally) seems to have a long 'drop' to it which might help with the latter, not sure about the former . . . .

BigG
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Re: Advice about uphanger fitting

Postby BigG » 18 May 2014, 6:00pm

I had the same problem with a Campag headset on a Frddie Grubb frame. I just filed a small channel in the back of the uphanger to clear the bottom race. It works fine.

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CREPELLO
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Re: Advice about uphanger fitting

Postby CREPELLO » 18 May 2014, 10:31pm

BigG wrote:I had the same problem with a Campag headset on a Frddie Grubb frame. I just filed a small channel in the back of the uphanger to clear the bottom race. It works fine.
Are you not anxious that the cut would lead to a stress raiser on such a stressed place? I would be myself, but perhaps your cut was small and smooth.

I've used both down and up hanger and can't say that I'm overly impressed with the uphanger. If it stops fork judder, then it's worth using one, but mine never reduced brake squeal. Also, watching the hanger deform under lever compression didn't inspire confidence in the performance, albeit I was using a big wide Tubus spacer to clear the headset cup. Using the uphanger usually means loosing a good place to fit a light, or it will be difficult to fit one well.

That downhanger with the QR looks the business to me, especially for a classic looking bike. Lovely bike BTW Rob Jordan.

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CJ
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Re: Advice about uphanger fitting

Postby CJ » 19 May 2014, 12:40pm

robjordan wrote:
gaz wrote:I think the standard uphanger bolt is M5 and suspect the fork crown threading to be M4, which may complicate matters further.

Good point, that might be a further problem.

That little bolt looks more like M5 than M4 to me, which is good, except that the standard size for a fork-crown bolt is still bigger than that at M6 (6mm diameter). That's because its historic role is to secure the whole brake mechanism. The bending stress on the bolt securing an uphanger will not be as much as a regular 6mm brake bolt, that's holding the entire brake mechanism onto the frame, but nevertheless a great deal higher (and more safety-critical) than the lamp bracket or mudguard that M5 screw has been provided for.

So you definitely need to upsize to M6. Fortunately that is easy. The hole size to tap M6 threads is 5.0mm, so you simply drill out the existing M5 thread in the front of the crown (with a 5.0mm drill, obviously) and tap the new M6 thread. That's how Bob Jackson ought to have made the bike in the first place, since all front lamp brackets are sized for a 6mm bolt. (If you don't need that much strength, an alloy bolt will save more weight than downsizing by 1mm in steel. All my mudguards and bottle cages are fitted with alloy bolts throughout.)

Given a 6mm steel bolt: I think you're safe enough to space out the uphanger BUT: to keep the bending stress on this bolt to a safe minimum, it is important that the spacer spans the full depth of this rather shallow fork crown, especially below the bolt, and spans more than a couple of mm at the bottom edge of the crown. A round washer doesn't. I would cut a square block of aluminium to fit. You may not have access to such materials, so I'd suggest a couple of square nuts. M10 looks like it should be big enough.

A much simpler solution to judder is to fit mini-V brakes. It looks like this frame doesn't have enough clearance anyway for the limitations of such brakes in that regard, to be a problem.
Chris Juden
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Brucey
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Re: Advice about uphanger fitting

Postby Brucey » 19 May 2014, 5:46pm

FWIW I agree, you are best off with an M6 bolt and a well-made spacer on an uphanger. A thick washer (or another spacer) at the front isn't a bad idea either.

Notching the back of one? That could all end in tears.

cheers
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