Cable routing - there I fixed it

[Tad]

In true thereIfixedit.com style I have fixed the cable routing on my Trek 990 singletrack.

I'm using the frame as a basis for a rough stuff tourer and the standard front mech cable routing is just plain silly. LGF has an ingenious work around using a brake noodle:

I wanted a more permanent solution so out with the blow torch, silver braze and flux it was. I scavenged a cable stop and bottle cage boss from a scrap frame and this is the result, on Trek 990 with sensible cable routing and a front mech pulley that lets me run top or bottom pull mechs. While I was at it I filled some chain suck damage and fitted a chain pip in the inside of the chain stay (hence the scorching to the paint on the outside).

Not perfect but it will do. The fillet round the bottle cage boss is acceptable. It's quite simple to do, cheapest blow torch I could get from screwfix that I usually use for heating stuck BBs and a length of silver braze and some flux powder. Ideal for small jobs like this but will never get hot enough for structural repairs.

The key is getting it clean, file paint off down to bare metal, get all the bits of paint off with coarse sand paper. Prep the braze ons in the same way, you need gleaming steel with no signs of rust or paint. Mix a drop of water with some flux powder to form a paste and paint on to the area you want the brake to stick to. Heat the brazing rod with your blow torch to warm it up and dip the top inch in to the flux powder, powder will stick to it (called hot rodding don't you know). Put brazeon on the frame, heat, when the flux paste starts to run clear it's about hot enough. Touch the brazing rod against the join, keeping the heat on, and you should see it melt and flow along forming a beautiful fillet. It's really satisfying when it works. Wait for it to cool then clean off the flux residue (it goes black when it's exhausted). Importantly tap any cable stops etc with a hammer to make sure the join is strong. The last thing you want to do is to send the thing off for painting and them to fall off when the bike is assembled.

Now to find a brake cable hanger for the rear cantis.

Any who, that is what I did this lunch time. (I also took a file to the TREK that was cast in to the seat stay cluster.)

 

[drcarlos]

I think it's easier to post in here than my own thread, so I will ask the questions here.
I am planning on adding an additional brake stop to an old Kona frame I have (for V's for my eldest), got the stops and the frame is stripped and ready.
I have a go gas torch for plumbing will this be sufficient?
Also need a silver braze rod and flux so I was wondering if this set I found on ebay was OK http://www.ebay.co.uk/itm/Silver-so...316?pt=LH_DefaultDomain_3&hash=item3a6b834984

Thanks,

Carl.

 

[danson67]

Should be fine Carl, as long as it's definitely not electrical solder.
I've done 40% silver lugless (SIF 42) with a propane torch before. The lack of heat volume means it's not up to BB shells etc, but should be fine for braze-ons. You've already done the roller boss, so you shouldn't have any trouble. Only needs about 650 C so just wait until the flux runs thin and glassy.

Machined stops, with a concave surface to match the tube are better. If not, a small flat filed onto the tube side of the stop helps to prevent it from pinging across the room. Might need to make up a little jig to hold the stop too, as there's nothing much to keep it in place when the flux bubbles up and melts:

Basic:

or flash:

Make up 1/2 the flux as a thick paste, clean the rod off, don't forget to dip the hot rod into the powdered flux to protect it, and get everything really clean before you start.

All the best,

 

[drcarlos]

Will file the stop with my half round file to get a good match for the tube and use a set of mole grips to lightly hold the tube in place.
Other than that will just have ot see how it goes.

Carl.

 

[Tad]

What he said ^ piece of pi$$ keep things as clean as clean can be. It's quite satisfying when you get a nice bead of braze start to flow.

Good luck.

 

[danson67]

a set of mole grips to lightly hold the tube in place.

Best to use something with either weight or spring in it to hold the stop, rather than a fixed clamping force.
As the flux paste boils and melts, its volume decreases and the flux flows out of the joint. This reduces the grip of a fixture like molegrips and the stop can shift under the weight of the grips.

This is from a previous reply (Hi, Tad ):

If you're feeling pretty confident, the quickest and simplest way is to flux up the location of the guide/stop, then mix up a thick flux paste, smear the underside of the stop/guide, cut a short length of rod (3-4mm) pick it up with the fluxed underside of the stop. Hold it in place with an old pair of pliers from the top. Heat while lightly pressing down on the stop. When the flux is ready the rod piece will melt, line up and hold the stop in place and let the brass cool. Simple.

Alternatively, and probably more reliable; try laying a thick piece of wire ( mudguard stay?) onto the groove in the top of the stop. Clamp this onto the tube away from the stop. The spring in the wire will hold the stop firmly, but allow a bit of movement and expansion. Try to keep the heat off the wire, as it will loses its spring if it gets too hot.

All the best,

 

[drcarlos]

Well just had a go and the got the heat on, got the flux going and then rod hot, hot rodded the flux and went for it. The end of the rod melted off and stuck in a lump to the frame but another piece of rod came off at the joint and appeared to flow on the top half of the joint. So I waited for it to cool and it has indeed created a joint (withstood a solid hammer tap). So I tided the rough bits with file and dremel and turned it over and had a go at the bottom side of the joint. The lump of rod dropped into the gap between the frame and stop and stayed there, pretty much in one lump! Not even flowed just stuck! I think my gogas torch (just checked the flame temp is about 1225) so it could be too cool. Going to get my dads torch with MAPP gas and will re-flux it and try again on saturday as I think I should be able to just flow the small piece of rod that is there already

Carl