Cycling and bicycle discussion forums. 
   Click here to join our community Log in to access your Control Panel  


Go Back   > >

Bicycle Mechanics Broken bottom bracket? Tacoed wheel? If you're having problems with your bicycle, or just need help fixing a flat, drop in here for the latest on bicycle mechanics & bicycle maintenance.

User Tag List

Reply
 
Thread Tools Search this Thread
Old 10-20-10, 01:37 AM   #1
tetonrider
Senior Member
Thread Starter
 
Join Date: Aug 2007
Bikes:
Posts: 3,524
Mentioned: 18 Post(s)
Tagged: 0 Thread(s)
Quoted: 104 Post(s)
dead spot in first cm of brake lever travel - da 7800

hi!
i just installed new brake cables on 2 bikes. (switched from DA cables to yokozunas, a stiff brake cable.) one is da79xx and the other (the now spongy one) is da 7800.

for the 79xx build, i could not use yokozuna's oversized ferrules where the cables connect to the brakes (cable adjusting bolt); in fact, i could not use any ferrule as the fit was VERY snug. braking is phenomenal.

i didn't use ferrules for the da 7800 build either. the inner diameter of cable adjusting bolt seemed even narrower; i had to trim ~8mm of the cable jacket (including the steel spiral) to even get it to fit into the connection with the brake. the individual longitudinal strands of the housing are intact. braking with the 7800's was just fine before with the DA cable/housing, but the cables were old and needed replacing.

i used a dremel and made excellent cuts across the board.

the issue i have is slow return. the first time squeezing the 7800 lever feels great, but once i let up the cable doesn't seem to fully return such that the first cm of lever travel on subsequent occasions is totally soft before the cable bites. note: the lever itself returns just fine when i let go, but it feels as if the cable does not.

i've taken up all slack, but it doesn't make any difference in the 2nd and subsequent pulls of the lever.

could i have cut the housing too short, perhaps?
could the issue lie in cutting back ~8mm of cable jacket on the da 7800 build?
could the issue be too tight a bend in the cable? (it's no tighter than on the di2 build, so i doubt this.)

i'm open to any suggestions, but i've reached an impasse here, at least for tonight (it's 1:30 am).

thanks so much for any ideas!

Last edited by tetonrider; 10-20-10 at 01:53 AM.
tetonrider is offline   Reply With Quote
Old 10-20-10, 01:40 AM   #2
AEO
Senior Member
 
AEO's Avatar
 
Join Date: Jun 2007
Location: A Coffin Called Earth. or Toronto, ON
Bikes: Bianchi, Miyata, Dahon, Rossin
Posts: 12,258
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
front or rear?

it sounds like the cable is binding somewhere, the spring in the brake caliper is not returning or the soldered heads are not sitting inside the lever properly.

either that or the cable housing is slightly short or too narrow.
too narrow can sometimes cause the housing to sink deeper or pull all the way through inside the lever, although this is usually on cheaper levers.
__________________
Food for thought: if you aren't dead by 2050, you and your entire family will be within a few years from starvation. Now that is a cruel gift to leave for your offspring. ;)
http://sanfrancisco.ibtimes.com/arti...ger-photos.htm
AEO is offline   Reply With Quote
Old 10-20-10, 02:03 AM   #3
BCRider
Senior Member
 
BCRider's Avatar
 
Join Date: Mar 2008
Location: The 'Wack, BC, Canada
Bikes: Norco (2), Miyata, Canondale, Soma, Redline
Posts: 5,456
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by tetonrider View Post
hi!
....i had to trim ~8mm of the cable jacket (including the steel spiral) to even get it to fit into the connection with the brake. the individual longitudinal strands of the housing are intact......
Um.....say WHAT? Brake cable only has the spiral metal in it unless you are using the Jagwire or equivalent that has shifter housing like longitudinal strands. Or if this is some dual compression housing then by removing the spiral metal wrapping you have allowed the end to deform and that is likey what is jamming your cable. In any event you should not have to remove the outer jacket from the cable let alone any inner structural items such as you're describing.
BCRider is offline   Reply With Quote
Old 10-20-10, 02:37 AM   #4
dab3
Junior Member
 
Join Date: Nov 2007
Bikes:
Posts: 23
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
I had similar problem when I installed new brake cables. I took the cable out, applied more grease on cable and the problem went away. In my case, the cable was binding.
dab3 is offline   Reply With Quote
Old 10-20-10, 09:22 AM   #5
tetonrider
Senior Member
Thread Starter
 
Join Date: Aug 2007
Bikes:
Posts: 3,524
Mentioned: 18 Post(s)
Tagged: 0 Thread(s)
Quoted: 104 Post(s)
Quote:
Originally Posted by AEO View Post
front or rear?
both front and rear.

Quote:
Originally Posted by AEO View Post
it sounds like the cable is binding somewhere, the spring in the brake caliper is not returning or the soldered heads are not sitting inside the lever properly.
the soldered heads seem seated....until i pull the lever then they don't return.

Quote:
Originally Posted by AEO View Post
either that or the cable housing is slightly short or too narrow.
too narrow can sometimes cause the housing to sink deeper or pull all the way through inside the lever, although this is usually on cheaper levers.
i'm going to free the cable from the bar to test if it's too short.

these cables are, if anything, thicker than DA.

i did use ferrules on the shifter end for the first time ever -- but i used them on both da 79xx and da 7800 installs, and they're fine on the 7900, so that doesn't seem to be the problem.

Quote:
Originally Posted by BCRider View Post
Um.....say WHAT? Brake cable only has the spiral metal in it unless you are using the Jagwire or equivalent that has shifter housing like longitudinal strands. Or if this is some dual compression housing then by removing the spiral metal wrapping you have allowed the end to deform and that is likey what is jamming your cable. In any event you should not have to remove the outer jacket from the cable let alone any inner structural items such as you're describing.
these are yokozuna cables, not the da cables. you are right that the end i trimmed could be compressing. i'll test that. i have extra strands of housing.

the yokozuna outer is thicker than DA and the fit was too snug to get in the cable adjusting bolt w/ or w/o ferrule. i'll try harder today.

it fit into the 7900 (w/o ferrule) with major work.


Quote:
Originally Posted by dab3 View Post
I had similar problem when I installed new brake cables. I took the cable out, applied more grease on cable and the problem went away. In my case, the cable was binding.
one thing about yokozuna cables is that they are really well lubed, but maybe not.....
tetonrider is offline   Reply With Quote
Old 10-20-10, 11:54 AM   #6
BCRider
Senior Member
 
BCRider's Avatar
 
Join Date: Mar 2008
Location: The 'Wack, BC, Canada
Bikes: Norco (2), Miyata, Canondale, Soma, Redline
Posts: 5,456
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Quote:
Originally Posted by tetonrider View Post
....yokozuna cables, not the da cables. you are right that the end i trimmed could be compressing. i'll test that. i have extra strands of housing.

the yokozuna outer is thicker than DA and the fit was too snug to get in the cable adjusting bolt w/ or w/o ferrule. i'll try harder today.

it fit into the 7900 (w/o ferrule) with major work.
......
I haven't run into that sort of housing. But in any event you just set yourself up for a failure of the end of the housing when you trim back any of it. Remember that the housing sees the same compressive force in the housing as the cable has for tension. So if you trimmed back the end like you described you are likely setting the end up so that it compresses and deforms and wedges the cable at that point. If you don't want to go with housing that fits the calipers, frame cable stops and brifters then you should modify the parts by drilling or otherwise enlarging the seats where the housing fits so you do not have to alter the housing in any manner other than just ensuring a nice clean and square end cut.

If you don't want to alter the groupo parts then your option is clear. Switch to another housing that does fit cleanly and without modification.
BCRider is offline   Reply With Quote
Old 10-20-10, 02:54 PM   #7
tetonrider
Senior Member
Thread Starter
 
Join Date: Aug 2007
Bikes:
Posts: 3,524
Mentioned: 18 Post(s)
Tagged: 0 Thread(s)
Quoted: 104 Post(s)
fair enough. the housing fit into da 79xx (without ferrule, and just a little removal of the outer sheath to start it). i thought it would go into da 7800 just fine but only learned that at the last step. i may try to see if just with harder work i can get the end to go into the adjusting bolt w/o removing/unwinding any metal sheath.

i'll report back when i test more, later.

thanks!
tetonrider is offline   Reply With Quote
Old 10-20-10, 03:18 PM   #8
dperreno 
Senior Member
 
Join Date: May 2008
Location: Beverly Hills, MI
Bikes: '72 Fuji Finest, '80 Austro-Daimler Inter 10, '06 Fuji Team Issue, '06 Salsa Las Cruces, Nashbar Frame single speed
Posts: 566
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Would one of these work?

http://www.loosescrews.com/index.cgi...d=436299630200
__________________
Doug

'72 Fuji Finest
'80 Austro-Daimler Inter10
'06 Fuji Team Issue
'06 Salsa Las Cruces
Nashbar Single Speed
dperreno is offline   Reply With Quote
Old 10-20-10, 04:57 PM   #9
tetonrider
Senior Member
Thread Starter
 
Join Date: Aug 2007
Bikes:
Posts: 3,524
Mentioned: 18 Post(s)
Tagged: 0 Thread(s)
Quoted: 104 Post(s)
solved the issue but am off for a ride right now. i'll stop back later to describe what needed to be done. it was simple but not obvious to me last night.
tetonrider is offline   Reply With Quote
Old 10-21-10, 12:59 AM   #10
tetonrider
Senior Member
Thread Starter
 
Join Date: Aug 2007
Bikes:
Posts: 3,524
Mentioned: 18 Post(s)
Tagged: 0 Thread(s)
Quoted: 104 Post(s)
short version:
the whole issue was caused by stripping that ~8mm of housing to fit the brake cable into the da 7800 cable adjusting bolt.

longer version (how i isolated it, with a couple interesting findings):
1) i removed bar tape and removed the tape holding the cable to the bars for a straight routing, to rule out too short a cable length. no change -- still poor return.

2) i checked that the ferrule was seated in the shifters and that cable was seated in ferrule. looked good, but i took the opportunity to remove the shifters and make it perfect. no change.

3) i then removed the cable adjusting bolt completely. i noticed inside what appeared to be an embedded ferrule. it's not as though an old one was stuck--it appears as if one is installed upon manufacturing such that it slides in and expands. da 79xx's cable adjusting bolt just has a smooth inner surface.

i didn't see this when trying to install it last night -- not the best lighting, but i really didn't examine it either by removing the bolt.

cool -- that signified to me that one really doesn't need a ferrule on there.

4) i had 3 other sections of housing (i.e., housing wasn't pulled back) and decided to see if i could work one in. on the 4th end i tried, one slipped right in -- with minimal effort. the others would not go in (tried for at least a minute with each).

that prompted me to cut a new section (starting with the short section of housing from seatpost-ish area to rear brake) to test this. a few minutes later i had good return on the rear--great braking potential.

when i replaced the front hose, i had an instant improvement but it still was not 100%. i noticed the arch spring tension was a little lower on that brake. bumped that up.

i used the opportunity to regrease the cable adjusting bolts -- they were bone dry and had lots of dirt. i could probably do well to take the brakes off completely and clean them up. i do keep a clean drive-train, but there are a number of parts that i never think to dismantle. after cleaning them, i noticed how the dirt negatively affected the rotation of the adjusting bolt for making those little shoe clearance tweaks; they were much harder than they had to be.

for now, this solved the issue.

braking is POWERFUL on the da 7900 with the yokozuna cables. noticeable change from the already great performance with the da cables. shifting with the yokozuna derailleur cables is a touch smoother than the da cables.

so.....why didn't i notice this last night? the da 7900 was a very tight fit...lots of work to get the cables in the adjusting bolt. when i tried the da 7800, it was even tighter with the first 3 or 4 ends i tried. i'd assumed it was a no-go....it seemed way off. no ferrule would go in, either.

i found a cutting method that made the housing go in a little easier:
a) insert an old brake cable during the cutting (did that yesterday);
b) tape a guide to keep things straight (also did that yesterday);
c) instead of cutting just in front of the tape, actually cut ON the tape itelf (didn't do that yesterday).
d) do the clean up/grinding with the tape on.

this seemed to keep the ends of the housing even tighter. it was still a fair bit of work to get the cable into the adjusting bolt (similar difficulty as getting it into their ferrule), but once i knew it could happen with one strand, i stayed at it. we're talking like 5-10 minutes just to get the cable in there. would be nice if the yokozuna ferrule had just a hair of a flare to it. what would happen to me is just one piece of housing would get caught and bulge, and it was nearly impossible for it to seat.

the yokozuna ferrules are pretty nice. it's stepped down from 6-5mm. if it tapered from a hair over 6mm, it would make things even easier.

for yokozuna shifters cables, i used ferrules on all ends (shifter, frame, rear derailleur). for the brakes, i used ferrules on ends contacting shifters and frame but not the brake calipers.

if you made it this far -- congralations!

this was long-winded, but i hope it might help someone in the future searching for yokozuna cables, dura ace 7800 and dura ace 7900/7970.

thanks to all those who offered suggestions.
tetonrider is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off



All times are GMT -6. The time now is 04:01 AM.