AVID disc brake set up questions

[d_douglas]

Hello - MTB specific question here, but I am hope that some of you mechanic types might be able to chime in.

I bought a set of BB7 mechanical brakes from a forumite a few months ago and have just gotten to installing them. They are on and they work, but they are not set up properly, as far as I can tell. I realise that these aren't hydraulic brakes, but my understanding is that these are great brakes that come close in performance. Thus far, they feel a little less powerful than my Avid V's (no comments on whether disc brakes are worthwhile!)

The brakes were practically new but one of the rotors has a SLIGHT warp, so I have backed off the adjusters so I don't have to listen to the annoying mild scraping sound. If I back off too far, I have no power.

When I tighten down the cable, should I pull the arm all the way up (effectively maximising tension) or should the actuating arm be tightened down somewhere in the middle of its movement cycle?

If anyone has either a) Avid's installation instructions (not available on their website) or b) the three essential tips for setting these babies up, I would appreciate it.

I am excited about my first set of brakes and chose the Avids based on low cost and simple maintenance - two critical elements for me!

Vintage Rocky Mountain MTB post to follow in the next while. I love this bike!!

[zank]

http://www.sram.com/_media/techdocs/bbdb-mtn-160-install.pdf

Their instructions are very good, but a bent rotor can be annoying. I suggest setting them up per their directions and tweak them if necessary. I don't have any additional advice, as I have always set them up their way and have had luck.

No question in my mind that disks are superior to linear pulls for our wet and muddy riding in New England. A properly set disk brake should feel like a perfect V-brake, but in all conditions.

[d_douglas]

Why was I not able to find this? Perfect.

I didn't realise that touching the rotors was a 'no-no'. Oops. I am sure I did that at some point. I will work my way through the instructions and get them dialled. Yes - my Avid Arch Rivals are now retired from this frame - I am sure I won't go back to V's on my offroad bike!

Darren

[Dave B]

If you do it very carefully you can bend back your rotor into a true-er state. There are tools for this, but I would suggest you get a new rotor. Save the warped one for a back up if you need it.

You can touch the rotor all you want. However you will need to use an alcohol spray (I use disc doctor) to clean the oil from your fingers off. The only real issue is the part of the rotor that actually goes through the brake.

With regards to set up. Tighten the cable as you would a V-brake and then adjust the barrel adjuster on the brake lever. After that fiddle with the pads to get your ideal fine tuning. The spring on the actual caliper can be used for the amount of tension the caliper has. You want to release the lever and see/hear it spring back pretty quick.

These are great brakes. They can be very grabby coming from a V-brake, so be careful and do not grab too much front. I have a nice scar on my shoulder from learning that one! :beer:

[Mud]

It is probably that the person who owned the brakes before you did not break (?) them in properly. Brake pads are tricky and you can glaze them very easily by continued applied pressure when they are new. You may need new pads in addition to cleaning the rotors. Dawn works pretty well also.

Without a Park or Morningstar tool truing is a little tough but a small vise grip works also. However, the best tool for straightening is this:

http://www.performancebike.com/shop/Profile.cfm?SKU=6472&item=00-9506&slitrk=search&slisearch=true

Hope this helps,

[DfCas]

The activation arm should be fully relaxed when you anchor the cable.Do not pull it up into its travel,then anchor the cable.

A bent rotor can be straightened easily using a truing stand or your bike and rigging up a guage or guide.I have an Ultimate truing stand that works. you can use a small crescent wrench or 3,but clean the jaws with alchohol first.

Its pretty common for them to get bent,so buying new ones each time seems like a waste of money to me-Kinda like tossong a wheel that needs touched up.

dan

[d_douglas]

I don't get it - do I understand you correctly? You simply thread the cable, pull it taut, then secure it? Isn't that defeating the purpose of spring tensioners? I actually did that last night and it did nothing. When I tensioned the lever arm and secured it, it started working. After that, I fine tuned it so that it works OK - just not perfectly. I could ride offroad now, but they could be better, in my opinion.

I guess I am having a hard time imagining how they would work at all if you don't use the spring mechanism!?

[Dude]

You want the arm compressed just a little bit when you attach the cable, so the rebound spring actually does something. You are correct in thinking that.

Avid designs them so the actuation arm is at its most powerful (IE has the most leverage) when it is 90degrees to the rotor. If there is too much cable pull, or not enough cable pull, they won't be as powerful.

The BB7's are more powerful, and more efficient than the juicy 7's, when set up properly. However, the rear will always feel a little bit spongy just due to all the housing/length it has to run through.

[DfCas]

I don't get it - do I understand you correctly? You simply thread the cable, pull it taut, then secure it? Isn't that defeating the purpose of spring tensioners? I actually did that last night and it did nothing. When I tensioned the lever arm and secured it, it started working. After that, I fine tuned it so that it works OK - just not perfectly. I could ride offroad now, but they could be better, in my opinion.

I guess I am having a hard time imagining how they would work at all if you don't use the spring mechanism!?


This is from memory(I do not have the instructions in front of me)

The arm should be at the relaxed position(or very,very close).Anchor the cable. The rotor should be 2/3 of the way to the outside of the bike.Turn the inner red knob until the pad stops the wheel from turning. Turn the outer knob until the pad contacts the rotor. Squeeze the brake lever and HOLD. Loosen the caliper mounting bolts and let the caliper seat.Retighten the caliper bolts.Release the brake lever. Loosen the inner knob 2-3 clicks.Loosen the outer knod 2-3 clicks.

See what it feels like-make final adjustments at the outer red knob.Do NOT use the cable adjuster at the brake lever to fine tune the feel.Use the red knobs.

In my experience you can make very small adjustments at the cable adjuster at the lever,but Avid says use the knobs.

If you pull the actuating arm up,you lose travel and eventually end up with none. Use the red knobs to compensate for pad wear.

I usually adjust the spring tension to max on the arm.

[Orin]

I usually adjust the spring tension to max on the arm.

I add a coil spring around the cable between the actuator arm and the cable stop to give a little more return pressure. The return spring is pretty wimpy and the additional spring is pretty much necessary on a tandem rear brake...

Orin.