I certainly didn't start it, but I was convinced that this was my problem. How else can you explain the additional 30-40mm of additional cable now sticking out the back of my rear brake from where I've had to take up the slack?! Cable slip? pad wear? I'm pretty sure my pads weren't that thick.
Avid BB5 Disc Brakes - help/advice needed
- Thread starter lejogger
- Start date
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Tension greater on a gear cable than a brake cable? Surely not !
Globalti
Legendary Member
I could easily explain the extra 30-40 mm of cable - most conventional rim brakes will need that much adjustment beyond what the barrel adjusters can accommodate as the pads wear out. I have always found that half way through the life of the brakes I need to release the cable stay bolt and pull a similar amount of cable through, having first reset the adjusters back to their minimums.
As for gear cable tension, yes, the deraileur ends operate at a big mechanical disadvantage and spring tensions are necessarily high to overcome friction in the cable run - have you ever tried to move a derailleur by hand? How does the tension compare to a brake pull-off spring?
As for gear cable tension, yes, the deraileur ends operate at a big mechanical disadvantage and spring tensions are necessarily high to overcome friction in the cable run - have you ever tried to move a derailleur by hand? How does the tension compare to a brake pull-off spring?
Halfords. I know this, because when I suggested to one of my Dr. Bike attendees that they ask Halfords why the brakes were set to 'oh, shoot, it's not stopping' they did so, and Halfords told her that the cables always stretch. So there, Mr. GTI! (Hits head gently on wall....)
GrumpyGregry
Here for rides.
nowt to do with cable stretch. everything to do with cable routing issues and outer cable compression under force. BB's with full metal jackets+compressionless housings are amazing
As a relative newbie to cycling (3 years) and certainly a newbie to disc brakes, this is really helpful to know... This being the case, now that I've adjusted the cables to this extent, should this be the end of my woes apart from pad wear?
GrumpyGregry
Here for rides.
and how might one go about doing that. My LBS says "sorry mate can't get them"
MacB
Lover of things that come in 3's
- Location
- Farnborough, Hampshire
This and the link again that Greg gave near the start of the thread:-
http://www.twowheelblogs.com/avid-bb7-disc-brake-set-and-tuning
I have used the Goodridge compressionless outer both with flat bars and drop bars with crosstops and I've had no problems other than my lack of experience making the initial process longer. I have the linked instructions printed out and up on my tool wall in the garage, but I think I know them off by heart now. I would also guess that, even if you didn't want to replace the full cable run, just replacing the bit between crosstops and main lever could make a big difference. Due to the severe bends these bits of cables are forced through.
The only other thing I would add is to check the alignment of the disc brake tab itself. I do this by bolting on the IS adaptor on its own and spinning wheel/rotor to see if the gap remains constant, much easier to see this way than with caliper in place. This solved a performance issue I'd been having on a rear caliper, all I had to do was add in a spacer between adaptor and disc brake tab, for one bolt only. As you can buy official spacers for this very purpose I guess it's not that uncommon. The brake was still working before but I had to leave the adjustment slacker than I wanted, which was obviously accomodating the misalignment.
Oh yeah, and I had a go at revitalising some pads and rotors(from secondhand bike) via a dishwasher cycle, it worked very well.
Globalti
Legendary Member
You ain't going to get 'em from a shop! Shops just don't sell that kind of thing. You will get them from the importer because importers can usually get spares for the things they import. A friendly phone call ought to do it.
potsy
Rambler
- Location
- My Armchair
After another go at adjusting them tonight, I am coming round to your way of thinking re upgrading to BB7's 
Might just wait until the 1st service/check-up is done in a couple of weeks, will ask the lbs to re-set them and if they prove to be problematic after that then I will buy a front one to start with, as this is used 90% of the time.
That would give me a spareset of pads for the rear and a spare rotor.
Might just wait until the 1st service/check-up is done in a couple of weeks, will ask the lbs to re-set them and if they prove to be problematic after that then I will buy a front one to start with, as this is used 90% of the time.
That would give me a spareset of pads for the rear and a spare rotor.
GrumpyGregry
Here for rides.
"sorry mate can't get them from the importer" would be the gist. My LBS has never ever failed to get me a spare part from something every before btw.
inevitably they are available for sale in the states from a number of online retailers.
RecordAceFromNew
Swinging Member
- Location
- West London
Am not sure whether it is worthwhile economically, but think this might be what you are looking for.
Yes I have moved both front and rear derailleurs by hand. There may not be a great deal of tension generated by a brake pull-off spring, but there certainly is when braking hard. If the tension was higher on a gear cable than a brake cable then surely the gear cable would be the thicker of the two.
MacB
Lover of things that come in 3's
- Location
- Farnborough, Hampshire
the regular tension is higher on a gear cable however the amount of force/tension applied in use can be far higher on a brake cable, certainly if you brake hard it dwarfs the tensions put through a gear cable. It's to cope with those forces that brake cables are thicker and the outers are stronger.
Yes, that's how I see it.
