Recessed nut caliper brake on old frame

[Alberto]

Hi!

I have some nice brakes and a nice frame, unfortunately cannot mount them into it, because they are of the wrong "recessed nut" type, and the nut (outer diameter: 8mm) is way wider than the hole in the frame (designed to place an M6 bolt, so I guess it is like 6.5mm).

The first "solution" I could think of was drilling the existing hole to accomodate the 8mm nut (other people on the net seem to have done that), but obviously it takes some work and a lot of care: rear brake is sitting on an already thin bridge and damaging the frame is something I wouldn't risk.

Then I thought about rethreading the brake pivot bolt to M5, so that a recessed (sleeve) nut could fit in the hole. Now I know nothing about rethreaded strength or how the recessed nut mount really works internally, so....

From "dumb" to "genius", how would you rate my idea?

 

[BikeGremlin]

Hi!

I have some nice brakes and a nice frame, unfortunately cannot mount them into it, because they are of the wrong "recessed nut" type, and the nut (outer diameter: 8mm) is way wider than the hole in the frame (designed to place an M6 bolt, so I guess it is like 6.5mm).

The first "solution" I could think of was drilling the existing hole to accomodate the 8mm nut (other people on the net seem to have done that), but obviously it takes some work and a lot of care: rear brake is sitting on an already thin bridge and damaging the frame is something I wouldn't risk.

Then I thought about rethreading the brake pivot bolt to M5, so that a recessed (sleeve) nut could fit in the hole. Now I know nothing about rethreaded strength or how the recessed nut mount really works internally, so....

From "dumb" to "genius", how would you rate my idea?

One way to do it would be to drill an 8 mm hole in just the rear part of the fork (and the front part of the rear brake mount) - so just one wall, on the opposite side of where the brake is mounted, not both walls.

That should probably not weaken the frame much.

I wouldn't try that with carbon fiber, but I would give it a go with steel (and probably with aluminium too).

I would not make the brake mounting bolt any thinner.

Alternative is of course to get matching brakes and mount them, that is always an option.

Relja

 

[Alberto]

Thanks for your answer and your advice. Not really liking to drill/expand the hole even if it is a steel frame, so I guess it will get another brake set, or at least another front brake (recessed nut front caliper fits on the rear bridge with an external nut).

 

[Alberto]

drill an 8 mm hole in just the rear part of the fork (and the front part of the rear brake mount) - so just one wall, on the opposite side of where the brake is mounted

Quite interesting discovery: there is a full tube running from front to back of the brake mount, not just two walls.

So there is no way I will drill this part... somehow problem solved by itself.