Originally Posted by
cxwrench
This is step 4:
INSTALL THE CABLEPass the brake wire through the anchor bolt on the actuating arm. Cable slack may be removed with a fourth hand tool. Be careful not to advance the torque arm as you pull the cable. Tighten cable anchor bolt to the specified torque. Use the barreladjuster at the brake lever to remove any remaining cable slack (if there is any)
SRAM is giving conflicting instructions...above they say to 'not advance the torque arm' but below they say to do that.
They do say to use one of the barrel adjusters to make up for pad wear but I will stand by my advice. The further you move the torque arm forward and approach a 90* angle between it and housing stop arm you will lose power. Once you reach a 90* angle and pass it the brake will have virtually zero power. I have adjusted dozens if not hundreds of mechanical disc brakes over the years and I would never shorten the cable to take up pad wear. It's not at all hard to dial in a piston and move the caliper a bit, it's very easy. If this is a problem for the user they need to learn how to adjust the brake properly.
I'm looking at the angle of the torque arm and seeing that there is minimal change in the force vectoring of the cable as that angle closes.
The number of different Youtube videos on this subject is scary. But the principle for solid braking force is this. Make sure there's some inner pad standing clear of the caliper. Make sure the inner pad is close as possible to the rotor without rubbing, And make sure the torque arm is in no danger of closing completely before full braking force is applied.
To adjust a brake that has been aligned properly but has pad wear is, first adjust the inner pad so it barely clears the rotor, using the inner pad adjustment dial. This gives the outer pad something solid to push against when it makes contact with the rotor. This is where most of the braking force comes from. Next, adjust the free play using the red outboard BB7 dial, cable tension, or a combination of both. In the case of the BB7, it makes more sense to use the outer pad adjustment knob, unless it's already maxed out for some reason. Also, other brake models don't have this feature.
For new brake installation or complete realignment, I first make sure the inner pad stands a couple millimeters clear of the caliper body. If it's a BB7, I want the outer pad dial somewhere in the middle of its range.Then I mount the caliper loose and attach the cable so the lever travel feels about right when I clamp down on the rotor. I release the lever, tighten the inner pad dial two or three clicks, clamp down again, and tighten the caliper mounting bolts. This aligns the caliper to the rotor. Then I release the lever and retract the inner pad dial, usually two or three clicks, so the pad just clears the rotor, the point where you no longer detect rub. Then I adjust the outer pad clearance for free play, usually where contact is made at a little less than half of full lever travel. It usually doesn't matter whether you use the knob or cable tension because at this point you're just fine-tuning. Now test. You should feel a solid thunk when you squeeze the lever. If it feels like a moosh, that's the outer pad deforming the rotor as it over-reaches for the inner pad. It means you need to bring the inner pad closer.
As long as the torque arm is in no danger of becoming completely closed under full braking force, the most important thing is to get the inner pad as close to the rotor without making contact until the lever is squeezed.
This whole exercise reminds me of what a dandy piece of equipment the BB7 is. It really is the class act of mechanical disc brakes. If only Juicy hydros worked as well.