Swapping out disc brake calipers.

[Kim]

Of the top of my head:

Progressiveness is mostly a function of how close the stationary pad is to the disc, the smaller the gap the sharper the braking.  IME if you've adjusted to the point where there's no audible rubbing at all, the gap's probably a bit too big.  If it's not slowing the wheel down appreciably, let it make rubbing noises, at least until it's bedded in.

Best way to ensure the caliper is properly aligned with the disc is to slacken off the mounting bolts, dial in the pad adjusters until they clamp the disc tight (there's a asymmetric disc position in the slot given in the instructions that you should aim to reproduce), tighten the mounting bolts and re-set the pads.

They do bed in a bit.  Take it for a ride, making sure to do plenty of hard braking, and then re-adjust.

Cable 'stretch' happens in the usual way, though that's independent from pad adjustment on a BB7.

If it's none of that, I'd start suspecting contamination...

[PaulF]

Just checking that you have got MTB levers as well? The cable pull is different but I can’t remember which type pulls more...

Other than that the pads may need bedding in. Best way is to find a steep hill, get up to speed and put the brakes on hard and then release. Do this a few times front and rear and response should improve. Also try to avoid dragging the the brakes as that can cause the pads to glaze and you’ll need to repeat the bedding process.

If anything I find the MTB version better than the road ones, not that there’s anything wrong with the road ones

[Brucey]

degrease everything with brake cleaner and then deliberately bed in the brakes as suggested in the manual.  IIRC this involves successive hard stops on the flat.

I think it is not a good idea to try and bed  in brakes on a hill; instead of stopping you may end up braking more at constant speed.  As well as possible glazing, there are two main reasons for this being a bad thing;

1) one of the things you are fighting against is possible brake judder. Braking at near-constant speed may excite judder at a specific speed whereas in a hard stop you are soon through any one (potentially judder-inducing) exact speed.

2) There is basically no upper limit to the brake temperature (or the lack in uniformity of such) if you brake at constant speed on a steep hill. This is bad enough on a well-bedded in brake but in a new brake it can be disastrous.

Ok so its is hard work to do the bedding-in on the flat but it is a better idea so far as the brakes are concerned.

BTW if the cables are not good or not adequately lubricated/well prepped then the brakes will start out feeling crap and will stay that way. Ditto if the brake calipers are not aligned to the disc, too.

NB if you have MTB calipers then with road levers (by accident, with the wrong cable pull) then the brakes will be ferociously powerful but rubbing is never far away and the lever will come back to the bar too easily because the lever MA is higher but the cable pull is shorter.

cheers

[Trailrat]

So, the levers are Avid A3s. They were originally what was used to operate the rim v-brakes. And I fitted new cables and cable outer sleeves, the cable was greased as it was threaded through the sleeves. It's a full outer from lever to brakes.

Best way to ensure the caliper is properly aligned with the disc is to slacken off the mounting bolts, dial in the pad adjusters until they clamp the disc tight (there's a asymmetric disc position in the slot given in the instructions that you should aim to reproduce), tighten the mounting bolts and re-set the pads.

When I'm doing this, do I need to make sure the brake lever is depressed?

[Brucey]

not if the pad adjusters are wound in so the disc is gripped, as suggested.

cheers

[FifeingEejit]

big snip:  this involves successive hard stops on the flat.

If the pads are new then the process is

find a flat bit of road
find a brake marker on the road with lots of road to run onto as your first couple of runs are going to produce bugger all braking effort

hammer it up to the marker and pull both brakes on hard as if you're wanting to stop quick but not go for flying lessons
repeat the process until the rear brake locks up under the hard braking.

It should only take 5 or 6 runs to get the heat into the pads for them to be ready.
The manufacturing process and then transport leaves a layer of stuff over the friction material that you're burning off with this process.

[Brucey]

the bedding in process does several things

1) it conditions the surface of the disc, which makes sure that it is parallel sided (to a better tolerance than it was made to) and that the brake pads have a consistent friction coefficient against the discs all the way round (which they won't have to start with because of the ground finish on the disc amongst other things).

2) the pads are worn so that they make contact with the disc over their entire face, and there are not 'hot spots' which lead to trouble

3) the pads themselves are conditioned. Typically the pad face gets hot enough that the binder (in organic/resin/semi metallic etc) pads reaches a high enough temperature that it decomposes (i.e. melts then burns). If this happens in one go (eg on a long downhill) the result is usually catastrophic brake fade and/or pad 'glazing' where the face of the pad becomes almost impervious (rather than open) in texture and this means the brakes work less well, e.g. since there is nowhere for any gases that may be generated at the interface (as in normal braking) to go.

With new discs and new sintered pads that are well made, there is often a minimal requirement for bedding in. With used discs and any pads, or any other type of pads and new discs it may feel like the bedding in isn't doing that much and that you are wasting your time. Nothing could be further from the truth; that the brakes appear to work well once is not[I/] a reliable indicator that your brakes are bedded in properly.

cheers