help adjusting rear caliper

[Seth Cooper]

anyone have ideas to help me get my rear rim brake caliper dialed in on my V20?

I feel the cable housing I am using (shimano) is too stiff, it does not allow the one side of the caliper to move. I have the spring on the other side dialed up, but still can't get it to stay centered. So I have the brake set gap wide, which I don't really like

any advice would be appreciated. (SRAM RED calipers 25mm rims)

seth

 

[RojoRacing]

pictures would help but for starters is the brake mounted in the upper or lower position?

 

[Seth Cooper]

not a big image, it is all i have on my computer at present, but it gives you the general idea.

 

[MrSteve]

Is the brake cable housing (from the frame tube to the rear caliper) too short?
The housing must be long enough to allow the brake caliper to move freely.

 

[Seth Cooper]

Is the brake cable housing (from the frame tube to the rear caliper) too short?
The housing must be long enough to allow the brake caliper to move freely.

It feels like the cable is too straight. If I hear the pad rubbing on the wheel I can reach down and yank on it where it enters the frame by the front fork and get it to move off the wheel. It just seems like the caliper spring can't move the cable like it needs to.

 

[RojoRacing]

if you feel it's too strait that's the same thing and too short. Cables leading to mechanical devices that pivot need to have an arch to them for pivoting.

Also make sure the mounting bolt for your caliper is tight, you should be able to move the whole thing by hand as you originally described but it should take a fair amount of force and shouldn't be floating.

 

[Seth Cooper]

ok. that makes sense. I guess i need a large enough loop that the caliper can move the cable. I will play around with that but I feel like if I try to put a bend in the cable the stiffness of the housing will try to straighten it and just rotate the caliper until the pad is against the rim. But your point about tightening the mounting bolt is I guess what will prevent that.

Thanks

 

[hurri47]

ok. that makes sense. I guess i need a large enough loop that the caliper can move the cable. I will play around with that but I feel like if I try to put a bend in the cable the stiffness of the housing will try to straighten it and just rotate the caliper until the pad is against the rim. But your point about tightening the mounting bolt is I guess what will prevent that.

Thanks

That might help, but if I'm seeing the picture correctly, your cable housing is still too straight. When you actuate the brake, the cable housing needs someplace to go. The only place yours can go is straight back in line with itself. It takes a lot less force to buckle a column if the column is pre-bent rather that straight. That's why you see nearly every rim brake cable in the world with at least some bend in it between the brake and the last fixed point of the cable (in your case it appears that's the frame).

Mechanical disks don't have that problem. You can make those cables as straight as you want.

-Dan

 

[Seth Cooper]

well i'm missing something. I put a bend in the cable, and tightened down the mounting bolt as tight as I could make it. the calipers still pivot freely, and as a result, the bend in the cable is rotating the calipers and pushing the pad into the rim. How do I keep the calipers centered if there is a force (from the cable housing) pushing the arm down?

 

[RojoRacing]

sounds like you're missing a washer or something to keep the caliper tight. Hard to say from this side of a computer though. I say take it to a shop or friend who is mechanical and have them look at it.

 

[Mathew Fy]

Ditto Jason’s assessment. Make sure you have the serrated washer properly installed. The caliper should be tightly fixed to the frame.
See Sram’s installation video.

https://www.sram.com/sites/default/...anical_shifter_and_rim_brakes_user_manual.pdf

 

[Seth Cooper]

So I just needed to loosen and rotate the calipers and re-tighten, I don't know why brakes just seem to have my number. Thanks for the advice!

One other question, I created my cable bend by wrapping the cable with electrical tape to prevent it from going back in the frame. Seems a little sketchy, is there a better way to hold it in position?

 

[RojoRacing]

So I just needed to loosen and rotate the calipers and re-tighten, I don't know why brakes just seem to have my number. Thanks for the advice!

One other question, I created my cable bend by wrapping the cable with electrical tape to prevent it from going back in the frame. Seems a little sketchy, is there a better way to hold it in position?

The cable should be long enough that inside the main frame of the bike there should be a large arch so it is neutral when coming out of the frame and doesn't want to push out or pull back in. If by pulling it out and applying the tape you are taking up the needed loop out the front of the frame you will just need to replace the whole cable with a longer one.

 

[RojoRacing]

What you are doing with the tape is fine if you're not robbing from the front slack but to avoid a sticky mess later on I'd suggest a tight zip tie instead.

 

[Steve Short]

You can't create slack where the is none. You most likely need a longer housing and cable. You could take the housing out of its normal routing and just run it outside of the frame temporarily to see if the extra slack solves the problem. If it does then get a longer setup or get creative in the routing.