Bicycle Mechanics - Rear brake "through the seat tube" routing issue
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02-13-12, 05:47 AM
Hi, I have an older mountain bike that has the rear brake cable routed through a narrow piece of plastic lining that sort of goes around the seat tube. I can feel a lot of friction in the braking and was wondering if there is a better solution for routing this cable? The little "tunnel" where the brake cable is routed is *almost large enough in dia to fit a pice of brake housing, but it's not quite enough.
Anyone found a good solution to this? Ignore the Surly rear housing stop in the picture, it's just sitting there in case I just opt to run full housing back to it.
02-13-12, 07:09 AM
I see you're experimenting with a housing stop hanging from the seatbinder. I always thought this was an OK method but never had much experience repaining 5 to 6+ yo bikes with them. I assume you tried simply replacing the plastic liner? I believe that is the same stuff they use/used to cover the cable between the housing stops and should not be too hard to source at your LBS
I think I see a paint chip or nick you don't have a dent or kink in the tube do you?
What kind of bike is that?
02-13-12, 07:26 AM
That routing is doing the same job as a cable hanger would, you could get a cable hanger which sits on the shaft of the seat post QR to elimiate this (the Surly device looks to be this? fuzzy photo so hard to tell what it's doing), but you still need somthing there to guide the cable.
02-13-12, 11:08 AM
What condition is the plastic tube in? Slide it out of the metal guide to look. How about the brake cable? Any kinks or corrosion? Do you put any lube in there?
02-13-12, 11:35 AM
The angle the cable's entering the seatpost guide from isn't very pretty. Cable will saw through that black liner after a handful of brake applications. You could just run housing all the way back to that silver cable stop you have. Zip tie housing to top tube.
Something about current setup doesn't seem to be as intended by frame designers.
02-13-12, 11:44 AM
Did a through the seatpost cable hanger on my AlAn Cross Super, in the 80's
my [late] father , a retired Machinist, made an internal roller that fit inside
my 25.0 Campag super record seat post.. .. came out clean looking.
sold off the frame, taller rider didn't need my seat post.
The small braze on noodle is a nice system and doubles as the hanger saving you an extra part. However this builder flubbed by making it too short to five a fair lead to the brake.
No matter what you do, there's a bend involved going from the top tube to the brake, but the short noodles end means causes a sharp corner which is probably the problem.
. Since you already have a liner there's obviously enough room. You can buy teflon or High density poly ethylene HDPE tubing, and cut a short length as a liner. Make sure there's enough hanging out the back end to make a fair lead to the brake, otherwise the cable will be sawing at the sharp bend at the end of the noodle, which is probably the problem.
You might try threading 4mm index housing or a brake housing stripped of the outer cover as a liner. The added stiffness will help soften the last bend into a gentle curve.
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