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Weak rear brake on new build

Old 03-21-21, 08:02 PM
  #1  
lajt
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Weak rear brake on new build

I hope people aren't sick of hearing about this build! I deeply appreciate everyone's time and wisdom, though; it's amazing how much I'm learning (also shocking how much there is to learn).
I started with an NOS pair of dual pivot caliper brakes, which were a good deal because they're a mismatched pair of Campagnolo Veloce front and Potenza rear.
The brake levers are inverse bar-end Tektros, which I tripled-checked are meant for calipers and not linear/v-brake.
Cables and housing are new of course.
Upon install, the front brake feels solid when you pull the lever. The rear, though, felt "stretchy"/spongy/weak, however you word it; the pads would contact but you could keep pulling the lever until it bottomed out.
I tried the pads closer to the rim, verified that all the housings are seated but same thing.
My first theory was, "could it be the brake caliper arm flexing"? It seemed unlikely, but these are literally the first Campagnolo parts I've ever touched, and the rear brake arm is hollowed in the middle, plus the rear is a different model than the front, so I figured, maybe this is a known issue with this one model of the Potenza only?
So I bought an old Dura Ace rear brake on Ebay just to test, and it felt exactly the same.
My next theory was perhaps the levers, being pretty cheap, have bad tolerances and have play in them, but this theory seems undercut by the fact that the left brake feels solid when I pull it.
It seems to me now like it must be something with the cable housing--maybe it flexes somewhere when I pull it and it loses some tautness. It's a pretty long run, and I have it wrapped under the handlebar tape, which is something I've never done before, plus the frame has internal cable tubing, so I suspect I did something wrong either at the points where the housing terminates in the frame, or in that long run under the bar tape.
I watched the Park Tool videos by Calvin Jones about taping and installing housing, which are excellent and informative, but I still suspect there's another piece of info I'm missing. Pics follow:










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Old 03-21-21, 08:46 PM
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nlerner
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That's a sharp setup! It's possible that your right brake housing is creeping into the lever body. I've seen this happen where the housing just kind of peels back while the inner coil moves into the space where you don't want it. Did you use ferrules at the levers to terminate the end of the cables?
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Old 03-21-21, 08:54 PM
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Yeah, Iíd guess you donít have some rigidity (like a cable end cap) somewhere like right at the lever body or as it enters/exits the frame. I donít have any internal-routing frames, so Iím not familiar with the ins & outs (pun intended) of that.
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Old 03-21-21, 08:55 PM
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I had the same problem on my Giant when I first got it (given to me as junk). I initially put on new Bell cables that I picked up at the hardware store for cheap just so I could get on the road with it. Real quick I discovered there is a real difference in low quality cable housing and better stuff. I replaced the cable housing with good quality, made sure there wasn't any extra length to flex, made sure all housing ends had ferrules, and what a difference. It wasn't the levers or the calipers, it was all cable and housing. I ruled out pads because you already put some good ones on. HTH and Good Luck
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Old 03-21-21, 09:11 PM
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Bigbus , that's an interesting thought about higher quality housing. Is there a brand that's known as the good stuff? I just ordered a no-name pack with the levers, but it seems like an easy fix to try.
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Old 03-21-21, 09:17 PM
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nlerner , I used ferrules where they would fit, but in a couple of spots, like where it enters the frame, the hole isn't wide enough for one. I can't remember if I have one inside the brake lever--that might've been another spot where it didn't fit. It's a good point, though--I wonder if there are narrow-format ones that I'm supposed to be using in spots like that.
Getting the length right is quite an art; there doesn't seem to be an absolute gauge. Even Calvin Jones gets a bit nebulous on this point; he just says, "if it starts to pull tight, it's too short, but if it loops too far out, it's too long."
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Old 03-22-21, 05:51 AM
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A step-down ferrule might be what you need.

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Old 03-22-21, 07:36 AM
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It's pretty common to have this with a back brake.
First is there anything wrong with the brakes?
Do they brake?
Do they snap back and the wheel spins freely.
How many fingers do you need to pull the brake? Front and rear?
Will they lock up?
Setup the brakes so the pads are against the wheel. How far can you pull the lever now.
You have to judge how much power you are going to need. Set the brakes and lever so that, that power is available without difficulty
If the lever comes to the bar before that point you have a problem.
Sometimes you have to live with it.
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Old 03-22-21, 08:26 AM
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Since you are going to go out and buy new housing anyway you might try running the housing along the top of the top tube secured by three pieces of electrical tape like old school (1980s and earlier) bikes. See how that feels. Then rerun it inside. Now you know how much the turns at the entrance and exit are costing you.
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Old 03-22-21, 08:35 AM
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nlerner , thank you about the step-down ferrule! I didn't even know those existed. Velo Orange carries those; I'll order a couple and try them.
79pmooney , that's a good idea about running the housing on the outside and see if it helps.
blamester , all good points. I'm going to take it all apart and re-run it front to back and see how it works.
Have any of you tried compressionless brake housing? I was reading about it and it sounded kind of intriguing. More expensive than gold, though!
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Old 03-22-21, 08:48 AM
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I haven't tried compressionless housing. but the housing I got at the LBS was much stiffer than the cheap stuff I got from the hardware store. But then I paid more for the couple meters of housing than I did for the complete Bell cable package that included shifting and braking cables, housings, and ferrules LOL.
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Old 03-22-21, 09:53 AM
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@lajt - Quality housing is provided by Jagwire, Shimano, and my favorite, Campagnolo.
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Old 03-22-21, 10:06 AM
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lajt
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Originally Posted by SJX426 View Post
@lajt - Quality housing is provided by Jagwire, Shimano, and my favorite, Campagnolo.
Thanks for the tip--actually just ordered some Jagwire.
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Old 03-22-21, 11:48 AM
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So new brake cable may make a difference but it's unlikely to be huge.
I maybe should have been clearer. Set up the brake with the pads against the rims before you pull the lever. Use the Barrell adjuster to tighten it up snug. Now pull the lever. How much can you pull. A new cable might get you couple of mill. Is that enough?
So it could be you that is out of spec for the lever. That may be designed for a different hand rider combo. And you fall out side the optimum user.
Building a bike is trial and error. You don't get it right first time. And everything is compromise. Asthetics and function.

Last edited by blamester; 03-22-21 at 12:06 PM.
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Old 03-22-21, 11:59 AM
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That doesn't look like brake housing to me.
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Old 03-22-21, 12:06 PM
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Compressionless housing ftw.
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Old 03-22-21, 12:10 PM
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Originally Posted by blamester View Post
Building a bike is trial and error. You don't get it right first time. And everything is compromise. Asthetics and function.
Thanks for this--it's reassuring that this is normal for a build! It always feels like there's some magical answer I'm missing, but I guess it's just part of the process.
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Old 03-22-21, 04:37 PM
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Originally Posted by lajt View Post
Thanks for this--it's reassuring that this is normal for a build! It always feels like there's some magical answer I'm missing, but I guess it's just part of the process.
It's easy to buy a 105 group set or whatever and stick on and it will work. But it is designed for everybody. Building your own is better but more difficult. I am getting close on my bike and it's taken years.
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Old 03-23-21, 04:58 AM
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The op's pics show a cable run with multiple S-shaped bends.

A moment's thought should make it apparent to any cyclist that the cable inner when taut will "cut the corners" of an S-bend and that's what causes the "stretchy" feeling. This will happen even with compressionless housing, as what happens is the inner just increasingly takes up the clearance between it and the outer. On single curves it takes it all up at once, then no stretchy feeling after.

Unfortunately the op's choice of bars/stem/levers/wrap and the internal-routing make it difficult to avoid such bends.

Internal routing, like seatpost flutes, is almost always a bad idea.
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Old 03-23-21, 09:40 AM
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As a side comment, bought a bike last year- brakes did not feel right- the seller had taken it to a shop for new brake cables and housing and they used Shift Index cable housing.

aaack!
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Old 03-23-21, 12:25 PM
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Originally Posted by lajt View Post
Have any of you tried compressionless brake housing? I was reading about it and it sounded kind of intriguing. More expensive than gold, though!
I’m using compressionless housing from Jagwire on the ‘79 Miyata with Shimano dual pivot caliper, Campy Ergo levers, ferrules everywhere, slightly toed-in Kool Stop salmon pads. Extremely pleased with the solid feel, especially considering the rear brake has full length housing. Same feel for both brakes. However, my housing is fully exposed, so fewer bends.
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Old 03-23-21, 04:41 PM
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Originally Posted by trailangel View Post
That doesn't look like brake housing to me.
Yes, @lajt are you definitely using brake housing?

Brake left, shifter right

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Old 03-23-21, 05:03 PM
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hi @tricky, yes, it's definitely brake housing, but that's a really good point--that would definitely cause it.
I bet I've unwittingly made this mistake many times in the past because I didn't know the two were different for most of my life.
On this particular project, I had watched the Park Tool video where he shows the difference between the two--how the shifter housing uses strands, whereas the brake housing uses a single coil, so I was aware of it going into it. I thought it was interesting how he uses cable cutters for the shifter housing, but side cutters for the cable housing. That's a distinction I will probably need to look up the next time I do this in a year.
I'm going to try the compressionless housing just to see what it's like. It's all educational for me so I don't mind spending the extra even if I don't end up using it.
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Old 03-23-21, 07:21 PM
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I suspect that the spongy feeling is a combination of inexpensive cable, inexpensive housing, and the levers themselves.
Putting together ‘the whole package’ can be an iterative process, and it is different for everyone/every build.
For example, on my 78 Davidson with first gen DA, I was unable to get the kind of braking performance I needed.
Wound up with dual pivot brake calipers and later Shimano SLR non aero levers to make it all function the way I needed it to.
Someone else might have been perfectly happy with the original levers and calipers and pads,but they didn’t stop well enough for my needs.
So...there’s that.
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