zze86

Rescued a Trek 7.1FX which basically needs EVERYTHING. Unfortunately, during disassembly I found one of the front brake posts had broken off.

https://www.flickr.com/photos/422775...posted-public/
(hopefully, the link works. On mobile.)

The fork is steel and the posts are NOT replaceable, they are welded in. Short of buying a new fork or getting a welder to put a new post on, I figure I have two options:

1) Buy a threaded replacement post and cut the pivot stud portion off the new post. File the broken stud on the bike as flat as I can get it. Get a long bolt, then order of assembly = bolt, brake, pivot stud, bike.

2) Buy two replacement posts. Cut and file off both existing posts leaving only the adjusting plate. Drill and tap a new hole for the new posts. Install new posts.

Anybody tried either or? Obviously the 2nd option is more time consuming but this bike was neglected pretty bad and the other post doesn't look that great either. I have the tools but wanted perspective.

I know it's not a particularly valuable bike but it looks to fit me and would make a great candidate for next year's winter beater.

Andrew R Stewart 

QBP and Problem Solvers use to offer FS1067, a canti stud shaft replacement kit. This was a cylinder with an OD matched to a canti post shaft, length same and ID smooth to pass an M6 bolt through it. One would file down the broken remainder, of the OE shaft, so the boss's base was flat. The cylinder was inserted into the arm and the bolt clamped the cylinder to the base. Retail cost was about $6.


I have done a few of these, always not liking the repair but was pleased with the results.


Being that it's the fork the obvious solution to retain a canti/linear brake is to replace the fork. A shop that cares about their liability really should not do anything other these days.


Am I two faced in this? I care to think it's my learning better then what I knew before. Andy

nfmisso

I 2nd new fork. If you count labor costs at all, it is the least expensive way to go. I doesn't have to be a Trek fork.

skimaxpower

Swap in a different fork.

You could even use this as an opportunity to swap in mech disc brakes.

CliffordK

Tektro also makes long reach calipers

fietsbob

Steel? sand blast off the paint and hire a framebuilder to braze on new bosses.

and perhaps you need a booster arch to be able to resist the forces that broke the last one.


my winter beater has hubs with drum brakes , you can then just ignore them..




...

AnkleWork

If you go with any bolt-on replacement (kluge or purpose built) consider adding a "brake booster" to support the boss at the outer end.

DiegoFrogs

If the internal diameter is small enough inside to fit a thread-in boss, I would tap it and bolt one on without hesitation.

zze86

So I decided to go route 2. Went to the LBS and asked about it and they gave me two posts for free in exchange for letting them know how it went.

Happy to say it went really well. Dunno if I would do this if I didn't have all the tools already, especially the drilling part. Really must be put on a drill press with a good vise to hold the fork down in order to drill straight. Just to outline the process in case somebody finds this and is interested in doing it.

1) Hacksaw off the posts flush with the mount plate. Use a medium to fine tooth blade. Use the mount plate as your guide.
2) File the cut flush with the mount plate
3) Drill the new hole for the new brake post. Be sure to drill over the mounting plate's post as much as possible. Trying to use the existing hole as a guide won't work. Remember, this post was welded on. Good welds penetrate through the base metals. So your hole may not be directly over the mounting plate's post or even round. This really must be done on a drill press with a good vise. I was given an M10x1.25 replacement post which requires an 11/32 drill.
4) Tap in new threads with a M10x1.25 tap. Make sure you go straight!
5) file off any burrs or use a deburring tool.
6) give the mounting plate a quick blast of paint to prevent future rust
7) install new posts!

Drilled and tapped


painted with one post installed


back with the frame

Kontact

Nice work!

Why did you decide to replace both of them instead of just the broken one?

zze86

Preventative maintenance/being paranoid. I don't know if you can tell from the pic in the original post but the other post was fairly rusty as well. I figured since I had the fork off, getting all setup to do the broken one and had the extra post, I may as well. Didn't really add much more time to do the second one, maybe another 15 minutes.

DiegoFrogs

Solid work!

That's a nice-enough bike that a replacement fork would have been worth it, too, but the work you did is every bit as good as the original.

When a pivot ripped off in my hand on an old $5 mountain bike that I ride a couple weeks a year, I did something similar. I passed my threaded mount into a sheetmetal box that was brazed onto the frame and used a nut on the backside that I ground to fit. In my case, it seems solid enough. In your case, I would be totally confident.