Have I bought the wrong brakes?

[r80]

So after months of carrying on without rear brakes I have been bought some new brakes (callipers, levers and all), but the callipers don't seem to fit.

This shows the attachment on the frame of the bike.

On the right is the old brakes, the left is the new ones. On the old ones the screw goes all the way through, but the new ones only about 2/3rds of the way.

This leads me to three possible conclusions

1. I've bought the wrong product
2. There is a piece missing
3. I am supposed to take the screw out of the old one (I have tried without success)

Can anyone help me out?

The brakes were Clarks.

Also apologies for the quality of the photos.

 

[fossyant]

The part you need is stuck in the old brake. They are generally a whole piece and dont have the boss that unscrews. You need that part refitting.

 

[r80]

One of them is off but it is insanely tight, probably machined in. Can the boss's be bought individually if the other one doesn't come off?

 

[fossyant]

The boss should be on the frame and not in the old brake. If there is a thread on its outside then maybe they are removable but they generally arent. The boss is just a hollow post that the brake slits over and you secure with an Allen bolt. You need the posts on the frame

 

[r80]

You can see by the thread on the frame that it was supposed to be removable.

 

[fossyant]

Not in the photos as they are blurred

 

[mickle]

You can see by the thread on the frame that it was supposed to be removable.

Not 'supposed to be removeable' so much as 'that's how they attach'. The vast majority are never removed for the lifetime of the frame.

 

[r80]

The vast majority are never removed for the lifetime of the frame.

Mine came off from the frame very easily, but were nearly inseparable from the screw. The boss came off from the frame when I was just loosing the screw with a rachet, like they were one part.

 

[HovR]

As others have said, you've left the brake boss (or pivot) in the old brake, where it needs to be attached to the frame. There should be some spanner flats on the boss so that you can grip it with a spanner and undo the allen bolt holding it on to the brake. If you're having issues then soaking it in some WD40 or similar may help. It's best to reapply the boss with some threadlock on the threads and lubricant on the pivot surface.

Quite often the bosses are removable on frames/forks which accept both rim brakes and discs, to allow you to remove them and plug the holes when changing to discs. It is possible to buy new pivots, although when I looked a while back it was strangely difficult unless you want to spend extra on Ti. Best just to reuse the old ones.

 

[mickle]

Cantilever bosses are invariably made of steel (the exceptions being Ti).

On steel or Ti frames they are welded or brazed and permanent. On alu frames they are attached by screw thread and usually with the help of threadlock.

If the torque required to remove the cantilever attachment bolts from the bosses exceeds the torque required to unscrew the bosses from the frame - either through corrosion (lack of grease on the bolt) or thread damage (cross threaded or just shoot parts) - then the bosses will unscrew from the frame.

And removing them from the brake without wrecking something is a fricking nightmare.

Time to consider new bosses. IMO.

 

[r80]

Thanks for your advice everyone, both bosses are out and undamaged. New brake is working well too.