Thorn Nomad fork rack mount

[il padrone]

Hi, been away for a long time. I would value any input about this minor crack in the powdercoat which has appeared right beside the front rack mount on this 2 year old disc-fork (Thorn Nomad Mk2). The bike has had limited use due to COVID lockdowns but has been on a couple of 3-5 week tours in the Australian mountains and outback, carrying 15kg on the front panniers.

Can it be left alone, or should I be looking to get it rebrazed?

[mickeg]

If that was mine, I would be asking Thorn about warranty coverage.

[Danneaux]

If that was mine, I would be asking Thorn about warranty coverage.

<nods> I would be doing the same. First move would be to send photos from several angles taken in bright light as clear and well focused as possible so Thorn can fairly evaluate them and advise on next steps.

Speaking as an amateur framebuilder, it appears from this photo this is not superficial to the paint only and there has been some movement between the boss and the fork blade, indicating a fractured braze. This can occur from any number of conditions but best have Thorn examine it to get the final word.

I have rebrazed fractured rack bosses on other makes and they came out successfully so if that is in the works there's a good chance of success, albeit at the cost of some local paint damage requiring touchup or a respray.

Best of luck, Pete; please let us know how you come out.

Best, Dan.

[martinf]

Agree with the others.

If it is a braze failure, the consequences could be nasty (front rack going into wheel ?).

If it is not possible (or too much hassle) to get the fork reviewed by Thorn under warranty, I would strip all the paint of the area to check the brazing, then probably get the advice of a local framebuilder whether the fork should be repaired or replaced. That's assuming you have a framebuilder reasonably near you.

 
 

[il padrone]

Damn! I have a two week tour to Kangaroo Island that I am leading in 6 weeks. No real other bike to ride for such a trip, and a fork return to UK is pretty much out of the question. Hmm...

[PH]

Which braze on is it?  And why is there a spacer?  Also do you have a rack with a rigid over wheel hoop?
Depending on which braze on it is, you may be able to get an additional fitting (Or two) somewhere to support it, Tubus make some clamps (See below), but even something as crude as a couple of jubilee clips will take the weight, just keep an eye on them and protect the paint.. If the spacer isn't strictly necessary, remove it, or at least don't use one any thicker than needed, the spacer simply creates leverage.  That's not a criticism, sometimes it's inevitable, an alternative is to use a longer screw from the inside of the fork, then a nut tightened onto it instead of a spacer, leaving you with a threaded stud to attach the rack to.  Lastly, if you don't have a rigid hoop on your rack, I thoroughly recommend you upgrade, not only is it a more rigid structure, in the event of a failure it's less likely to be catastrophic.


https://www.tubus.com/en/products/accessories-front-carriers/tubus-product/lm-1-mounting-set-for-forks-without-eyelets

[mickeg]

Damn! I have a two week tour to Kangaroo Island that I am leading in 6 weeks. No real other bike to ride for such a trip, and a fork return to UK is pretty much out of the question. Hmm...

If I was you, I would state that when you contact Thorn, and as Dan suggested, some better photos.  Do you have access to a camera with a macro setting?

[il padrone]

Yes, that photo was just a quick shot with the phone cam. I have several much better cameras.

[il padrone]

Which braze on is it?  And why is there a spacer?  Also do you have a rack with a rigid over wheel hoop?

It is the fork mid-mount for the front rack. The spacer is required because of the width of the rack's double-mount; it is a Tubus Duo, no hoop over the tyre, separate racks each side. I guess that I could move the spacer to the inside of the fork, but this may get tricky with the disc-mount at the bottom. Shall check it out.

https://www.metrocycles.com.au/product/tubus-front-pannier-rack-duo-lowrider/

[mickeg]

If that is a crack in the metal, I would not use a rack like the Duo.  If you fell at speed, the side load stress on the mount might snap it the rest of the way off. 

[il padrone]

Better photos. I have emailed SJS Cycles for advice.

[il padrone]

Further to my fork rack-mount. After some discussion with Thorn about the crack, I have passed the fork on to a local trusted frame builder for repairs. After an initial examination he became suspicious that the braze looked to be silver-solder. Knowing this matters a lot for the repair. I have emailed Thorn for confirmation of what attachment media was used on the fork; waiting to hear any response about this. Time is pressing as I am organising a 2-week tour for a group commencing Saturday week, and I really NEED the bike to be right to ride.

Does anybody here have the knowledge to tell me whether a 2018-19 Thorn Nomad Mk2 disc fork has bronze-welded rack mounts, or are they silver-soldered? Can you confirm anything about the brazing media used.

[Danneaux]

Pete,

While I cannot speak to the method/media used on Thorn's forks, I can speak as a hobbyist framebuilder who has made and/or modified a lot of frames, racks, and so on over the last 30-odd years.

If the rack boss is stainless, then it is almost certainly brazed using silver-solder. Most brass fillers will not wet the surface of stainless, and if they do they will produce low-quality joints. As I recall, all Nomad bosses are stainless, but this can easily be determined once the boss is off and possibly while it is on (magnet, though some stainless still has some magnetic attraction).

If I were to do the repair, I would heat the boss to remove it so I could clean the base metal of the fork and the boss, then reposition it using some all-thread to align it with the boss on the other side and then solder-braze anew with at least 55% silver content rod.

It will not do to simply heat the joint so new filler can flow; this is something your framebuilder will know.

Hoping this helps.

Best, Dan.

[il padrone]

Thanks for this info, Dan. The Nomad's cable guides are all stainless; not sure about the rack bosses. I will pass your info on to the frame repairer, good point about a magnet to check if
it's stainless.

Cheers, Pete.

[Danneaux]

Pete,

I went back through my files and found Thorn indicates the Mk2 rack bosses are indeed stainless (see attached). Of course, this is for the original v-brake fork but I would be very surprised if they were anything different on the disc fork.

As a double-check, the fork rack bosses on my own 2012 Nomad Mk2 are also non-magnetic and don't recognize a magnet.

Good luck on your repair; please let us know how you fare after your return.

Best, Dan.