Rethreading a brake mount?

Newfish

Evening all,

I was wondering if someone could point me in the right direction, if there is one.

I have just serviced my mates bike for him as the headset had come loose and it needed a couple of other things doing. When I came to put it back together the top thread for the front brake has failed. My guess is that this is due to being over tighten when it was serviced recently, very boring, but there you go.

My question is this, is it possible to get them rethreaded? I did think about glueing it but he might want to remove the caliper in the future. If it wasn't the brake I would be to bothered, but it is, so I am.

Would loctight work?

Any ideas/solutions appreciated?

Thank you.

oxocube1

I assume you mean the thread in mount on the fork? Well you could possibly re-tap the thread but it depends on whether there is 'material' still there to be tapped. That is certainly what I would try in this situation. If it dosen't work I would not know what else to try!

zanush

If the thread is buggered it could be retapped bigger and a helicoil inserted, this means you can still use the original size bolt. This is one solution but the catch is whether there is enough material left to perform the repair.

cycleclinic

Tapping to M7 can work and fit a M7 bolt, it is a lot cheaper than fitting a helicoil. You you to tapped out to an M7 sort of size anyway to fit the helicoil. M7 bolts are often 11mm hex heads but that is not going to be a problem. An M7 tap and bolt is going to cost less than £10 has to be worth a try.

zanush

Or there is the method as described above I prefer to helicoil but that's only because i can do it at work.
Just be very careful if your going to try retapping yourself, a bit of cutting oil (wd40 at a push) on the tap threads will help to break up the swarf as you tap a few threads and back it off and continue.
An lbs would prolly sort it for you but will cost more.

Newfish

Thank you! I'll have a look into that. What do you mean by 'material left'?

I was tightening the top bolt of the front caliper post mount and felt the thread go so stopped. The bolt holds but only just and with the amount of force/vibration going on down there it won't last.

The retapping sounds like a plan.

Thank you all.

zanush

Newfish wrote:

Thank you! I'll have a look into that. What do you mean by 'material left'?

That's the material surrounding the tapped hole....not enough material and the bigger tap could leave the walls of the threaded hole too thin resulting in a much weaker anchorage point or even split the post mount. Without seeing it it's hard to say but if you go down that route make sure you measure up carefully first
First i would get a tap that is the same size and run it down threads, blow the hole out to clear any swarf and crap and use a new bolt with some threadlock.....if that doesn't hold i would look at the retapping bigger option.

nicklouse

dont glue or do any other fake fix.

either get it helicioled (if there is enough material to allow this) or new lowers will be needed.

if the bolt was originally too short check a longer bolt. you need a minimum of 4 threads in undamaged threads to hold it.

thelonegroover

You could try filling with an aluminium brazing rod, using a blow torch. Then re drill and tap.

cooldad

I wonder if the magnesium content would make them burst into flame?
Film it just in case.

nicklouse

cooldad wrote:

I wonder if the magnesium content would make them burst into flame?
Film it just in case.

not to mention the burnt paint and boiling oil and melted who knows what!

Newfish

nicklouse wrote:

dont glue or do any other fake fix.

either get it helicioled (if there is enough material to allow this) or new lowers will be needed.

if the bolt was originally too short check a longer bolt. you need a minimum of 4 threads in undamaged threads to hold it.

Thanks Nick, good advice as always, I shall investigate further and go from there, might include pics next time too.