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My rear brakes on two bmx's are bad. Both bikes have a u brake I think with the cable tensioners coming from the front. One bike has large koolstop pads and neither of them work well. Not sure if it's down to set up, but both used to better than this. Both sets of pads have enough material left on them so are not worn. The only thing's I can think of is a good clean, or a change of setup.
Any advice?
Ah, the U brake.
My advice? Set aside at least an afternoon to do any work on the infernal thing.
APF
Replace the cables with better quality ones.
And new pads, the old ones have probably degraded with age.
Lube the bejeezuz out of the cable(s).
Run the straddle wire as short as layout will allow to improve mechanical advantage. (That was easier in days gone by when longer rear ends meant that the cable ran through the seat tube and the straddle behind it could be super short. You want to be pulling the arms towards one another rather than towards the head tube as too long a straddle will do).
Grease the mounts and spring/pivot assemblies.
Don’t go too mental with spring tension.
Pads run as close to the pivot as possible while maintaining proper pad/rim contact.
Clean rims and pads with windowlene.
thanks everyone.
Odyssey Springfield - best BMX brake IMO and not super expensive
Here's a picture of me in 1999 trying to set up my Odyssey Evolver on a T1 Barcode
They're always rubbish, they can be slightly less rubbish than a badly setup brake, but are still rubbish.
Fundamentally you've got the cast off brake design that even roadies don't use, coupled with a wheel with a much smaller radius (therefore the brake is acting on a smaller lever).
This is why there's a foot sized gap between the fork crown and the front tyre!
I disagree. Decent U-brakes set up well are great. Huge mechanical advantage is possible, but poor set ups and poor quality budget brakes mask that very well!
What you need to do is remove your current brake and find something called an Odyssey Pitbull brake and install that. Ride with that for a week, then re-install your current brake.
Hey presto- it more wonderful than you can believe it!
Clear pads for a locking brake.
Well lubed cables.
Straddle wire set up to pull to maximize mechanical advantage. Depends on brake and frame.
Clean rims.
Chrome rims are better than painted for "grabby" brakes.
Not hard u-brakes work very well are strong and fit out of the way.
Pitbulls were terrible brakes.
great lot's to think about.
They're not chosen for power but modulation (and small size).
However like canti's you can fiddle with a few (too many probably) parameters to adjust the mechanical advantage. The big issue is it's almost impossible to change one thing at a time.
both used to better than this
the other issue is the mechanical advantage changes as the pads wear.
I agree with all of the above, here is what I would do:
Take cable off bike and see if inner moves smoothly through outer
Pull inner cable from outer, check for damage and if no damage flush outer with GT85 or similiar
When reinstalling, check length of inner and outer, newer cables dont bind when the bars spin so long length is no longer needed
Check rear wheel is in centre of frame
Check pads for even wear, if one pad is more worn than the other, get new pads, install pads with the same washers each side, if old pads are okay, rub against a brick wall a few times or sand so rough
when applying spring tension, do the lowest amount needed so that the pads are equal distance from the rim
sillyoldman has nailed it. Could lock my rear wheel up no problem when setting a 'U' brake up like that.
A bit of reiteration to the above I guess, and for rear brake set up:
- Set the caliper tension lower than you would think to improve feel (they don't need loads, just enough to spring back). Also make sure tension is consistent for both calipers so as to improve consistency of bite on the rim.
- Take time to line up your brake pads with your rim so there is consistent contact across the rim, and across the pad when pulled (use the old pulling the brake lever whilst the pads are loose and then adjust method)
- Keep the straddle cable as short as possible (the main cause of spongy, non-biting brakes), and even consider a bit of manual bending of the straddle cable itself to remove the 'spring' in it.
- With the barrel adjuster at the lever wound out, tension your straddle hanger so the pads are touching the rim. Then wind back in your barrel adjuster (or straddle adjuster) so the pads no longer touch. Adjust for your own preference thereafter.
- Use a single slic cable set up. Don't bother with taking inners out and relubing etc; just buy a 'slic' cable and install. Simple.
- If your bike permits use this: Odyssey Quik Slic as it eliminates mechanical inefficiency at the straddle and is really, really good.
BMX brakes are super fiddly to set up right, but once you have done it correctly you can get consistent bite, and be able to lock up your wheel for tyre taps etc with a single finger. It can be be done - honest!