Ineffective front cantilever brake

[AdrianStone]

I've just received my bike back from LBS after a rebuild. They had called me to ask about the brakes as they admitted they had some trouble setting them up. The front brake mechanism has been changed, not sure how to describe it, but the photos show the difference between the front (new) and rear (previous) mechanisms. Both brakes had new blocks rear were Jagwire and front a Shimano set - I had both as new spares at home from when I bought the bike.

The front brake seems very ineffective, little braking effect, whilst the back wheel  can be locked with not too much effort.

Any thoughts... other that go back to LBS?

Thank you

New Front



New Front



Rear



Rear

[B cereus]

The Mechanical Advantage (MA) of low-profile cantilever brakes like those is at a maximum when the straddle wire is as low as possible; Your old set up used Shimano staddle links which to a certain degree help to achieve this. As a consequence, it also follows that the MA is regressive, in other words it falls as the levers are operated and the straddle rises. Lowering the new straddle wire by shortening it should improve performance, but you may have to fit a longer inner cable or shorten the outer cable to gain a little extra length.

Because of this regressive behaviour the MA at the point when the pads contact the rim will be decreasing as the pads wear.  Further shortening the staddle wire or moving the pads closer to the rim is the correct way to compensate for pad wear.

[PH]

What B cereus said. For low and mid profile brakes the lower the yoke the longer the virtual lever and the less pad movement for the same cable pull, less pad movement equals more force - If you imagine a horizontal line from the boss and a line from the yoke continuing through the attachment point, where they intercept is the leverage.
With wide arm canti's it makes no difference, the arms are already horizontal.

[martinf]

Any thoughts... other that go back to LBS?

Try different brake blocks, at least on the front? My own favourite is KoolStop Salmon.

[AdrianStone]

Thank you all for the advice, think I'll start with replacing the pads with Koolstop thin line salmon or dual and see how it goes before adjusting the straddle cable... lots to learn!

[mickeg]

I agree with what B Cerius said.

If there are any kinks in the outer housing, that could also cause extra friction.  If with one hand you move the brake lever in and out, the other hand you press on the bare cable to keep tension on the cable,  you should be able to feel it if there is any friction in the outer housing or perhaps a frayed cable.

You said nothing about the brake levers, so I assume they are the same as before.