Problem getting v-brakes working right

optimisticbiker
optimisticbiker Posts: 1,657
edited May 2012 in The workshop
Having problems getting front v-brake to engage/disengage properly. When I press the brake lever the RH arm (looking from front) moves in but the LH one moves only slightly until the RH pad contacts the wheel. Then the LH moves reluctantly. With the cable removed both arms move easily and the spring settings are equal. There is a slight dink in the pipe (noodle?) that transfers the brake cable into the caliper, tho the cable seems to move freely in the pipe and is well lubed. I'm wondering if this is impacting on the operation of the brake.

Any ideas?
Invacare Spectra Plus electric wheelchair, max speed 4mph :cry:

Comments

  • veronese68
    veronese68 Posts: 27,317
    Do you mean the spring setting is visually equal? I would just increase the spring tension on the one that is moving first until they move together. The v brakes on my old bike never had the spring setting looking the same, I always set them so they move together.
    Don't think it's anything to do with the cable attachment thingy.
    Kinesis Pro6
    Marin Nail Trail
    Cotic Solaris
  • optimisticbiker
    optimisticbiker Posts: 1,657
    No, I mean the tension is equal (checked with a spring gauge, i am that sad :lol:)... If I wind it out to a low but equal tension on both, then increase the tension on the moving one (the RH one, I had the same thought as you) I can wind it almost right up - it makes little difference. All it does is move the pad nearer the rim, pushing the whole assembly over, it doesnt affect the delta between the arms... as if the inner isn't moving back into the sheath.
    Invacare Spectra Plus electric wheelchair, max speed 4mph :cry:
  • veronese68
    veronese68 Posts: 27,317
    Swap the pipe thingy front to back and see if that helps. I've got an old set of Vtype brakes off an old BSO I ripped apart. I'm quite happy to post the thingy if you want.
    Checking the tension with a spring gauge. That's really keen. I doff my cap to one sadder than I.
    Kinesis Pro6
    Marin Nail Trail
    Cotic Solaris
  • The Rookie
    The Rookie Posts: 27,812
    you only need a tiny amount of difference in friction on the pivot for one to move first, also the outer cable from lever to the end of the noodle will add a preload either pushing or pulling that lever in or out. End of the day what difference does it make, you don't get any braking until both are on the rim, just ride the darn thing!

    Simon
    Currently riding a Whyte T130C, X0 drivetrain, Magura Trail brakes converted to mixed wheel size (homebuilt wheels) with 140mm Fox 34 Rhythm and RP23 suspension. 12.2Kg.
  • mudcow007
    mudcow007 Posts: 3,861
    have you got the pin (sets tension on the spring) at the back of the actual brake arm in the matching hole on both sides?

    on my forks i have 3 available holes (oow err)

    if these dont match you can same tension on the springs but they wont set up correctly!

    undue the allen bolt on the brakes take em off an give a quick check
    Keeping it classy since '83
  • optimisticbiker
    optimisticbiker Posts: 1,657
    new noodle and cable on order. Reckon its that kink in the noodle and a gunged up inner sticking... so easier just to replace outright.

    Only one hole in each fork so no difference. I've had the arms off, degreased them and refitted, newly greased on the sprung base with a drop of light oil on the pivot. They're about as frictionless as they're ever going to be.

    btw for checking the tension I used my digital fishing scales so the stiction was equal within 20g or so. Useful bit of kit (for weighing wheels etc too) and under £3!
    Invacare Spectra Plus electric wheelchair, max speed 4mph :cry:
  • neiltb
    neiltb Posts: 332
    also check the posts, take brakes off, clean post, lubricate (I use general purpose grease). As above set the springs in the same hole on each side and tighten them down. Does just sound like a spring tension issue.
    FCN 12
  • the_fuggler
    the_fuggler Posts: 1,228
    I'm bumping this thread to say thanks to all who contributed. I hadn't a clue what had happened to my brakes after changing the pads. There was no tension in the cable and brake lever and no spring in the arms of the brakes themselves. On closer inspection, I have the three available holes for the spring tension. I had no idea they were there, let alone what difference the would make, but, sure enough, moving the spring into the middle hole made all the difference. Brakes are now functioning perfectly and what remaining hair I have will now stay on my head rather than being torn out....

    Cheers!
    FCN 3 / 4
  • optimisticbiker
    optimisticbiker Posts: 1,657
    Glad it helped :) I'd forgotten about this thread, came across it while looking for another...

    The problem with mine, for the record, was that the arm was seizing onto the baseplate that holds the little tensioner pin that goes into the hole on the fork. It looks like its got slightly twisted, possibly collision damage, and over time has been rubbing until its seizing under load. Today I stripped it off the bike, removed the spring, put some flushing oil into the joint and managed to turn it round and round until it flushed out all the crap in the joint and was moving more freely (not perfectly free, but enough not to stick). Then I put some light machine oil on the joint and worked it back and forth until it felt a little smoother and refitted it to the bike. It seems to work now, although I have to have the pad close to the rim - if it gets a few mm away the arm sticks and doesnt return. So its fine with the bedded in pads i have now, but its likely to be an issue with new ones. Need to see if I can source a new arm - Tektro RX3 - no longer made :(

    <edit> Just ordered a pair of Genetic 85mm mini-V @ £8.99 bcge-mini-v.jpg
    Invacare Spectra Plus electric wheelchair, max speed 4mph :cry:

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