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Direct Pull / V Brake Issue

stevenlunnstevenlunn Posts: 4
edited May 2010 in MTB workshop & tech
Hi all,

I have a problem with my Promax V / direct pull brakes on a Trek 6700 from 2002. When I apply the rear brake lever, they both engage on the rims OK, but when the lever is released only one of the pads fully releases. The other side does not spring back (it's the side that the brake cable connects to). So after braking once that side rubs against the wheel rim slightly until I move the brake arm out by hand.

Some thoughts so far:

The wheel seems true. Pad alignment looks fine. Pad and brake arm bolt seem tight.

Not checked the noodle yet.

The small slotted screw on each arm - what does this do? Spring tension?

Not released the cable to inspect the pad yet - could it be something on there sticking?

If cable tension was not correct I assume both rear pads would be affected rather than just one?

Thanks.

Posts

  • DonnicDonnic Posts: 85
    Small screw is the spring tension for each arm.

    Tighter screw = more tension on the spring so the arm will come out further.

    Looser Screw = the opposite.

    Might be worth checking those, try turning in small amounts 1/4 to 1/2 turns; then give the brake lever a pull once to kinda reset the v-brake arms.
  • bomberesquebomberesque Posts: 1,701
    stevenlunn wrote:
    The small slotted screw on each arm - what does this do? Spring tension?

    Yup, as said, you need to balance the tension behind these 2 screws. it's a bit of a pita but worth the effort.

    also, if the bike is old / perhaps a bit undermaintained? stripping the brakes off and giving them some clean and lube love will help the springs to their thing
    Everything in moderation ... except beer
    Beer in moderation ... is a waste of beer

    If riding an XC race bike is like touching the trail,
    then riding a rigid singlespeed is like licking it
    ... or being punched by it, depending on the day
  • BG2000BG2000 Posts: 517
    Have you checked how the spring connects to the brake boss on the seat stay ?

    Sometimes the spring can pop out the hole when you pull the brakes, which means it won't spring back on that side. But when you pull the brake back again by hand the spring pops back into place. I've also seen this happen on brakes where the spring doesn't need to connect into a hole, and instead relies on the bolt tightness. The end result is similar.
  • stevenlunnstevenlunn Posts: 4
    Thanks for the advice people. Will give the bike another look at some point.

    About the lubrication of the brakes, I assume I should lubricate all the moving parts? And is that specifically oil, or grease?
  • bomberesquebomberesque Posts: 1,701
    I just strip them, clean them and give them a light oil with something 3-in-1 kind of weight (not WD40/GT85, it's too light and will evaporate off). the cleaning is the key, there'll be all sorts of sh1te in there.
    Everything in moderation ... except beer
    Beer in moderation ... is a waste of beer

    If riding an XC race bike is like touching the trail,
    then riding a rigid singlespeed is like licking it
    ... or being punched by it, depending on the day
  • stevenlunnstevenlunn Posts: 4
    Had a quick look this afternoon.

    I thought I would try and have a closer look at the pads first. It seeems very tricky to disconnect the cable that commects the two brake arms. If I squeeze the two arms together, I am almost able to lift out the metal noodle that the cable runs through, but it's not quite enough to allow the thin part of the cable to be near the small gap. Any particular technique anyone uses to do this?

    I don't notice any springs just from looking, but I guess I need to do the above at least so that I can see more of the brake arm.

    I did try adjusting the spring tension on the offending arm up to about half a turn, but this didn't make any noticeable difference. Might persevere with this more at the weekend.

    One thing I have noticed is that the rear brake lever is more wobbly than the front one. Not very wobbly, just more noticeable in comparison to the front brake lever. And sometimes it doesn't fully retract after pressing until you move the brake arm out again by hand. I guess that is because the brake arm is not springing back?

    Thought I'd mention the above in case it means anything to anyone......

    Thanks again.
  • supersonicsupersonic Posts: 82,708 Lives Here
    Are the brake blocks hitting the rim square? They are not undercutting in and sticking? [even slightly?]

    You generally need to turn more than half a turn.

    Also sounds like the cables are dirty - this stops the spring pushing the cable back through the outer.
  • The RookieThe Rookie Posts: 27,804
    The other thing that can happen is that (depending on design) the arm can bind on the post, my daughter had this problem, removed arm, cleaned up post and bush in arm, added a little coppaslip, refitted, sorted.

    Simon
    Current steed - Whyte T129, 2013 frame, mongrel Revelations, Giant dropper, Stans S1 wheelset. 12, Magura Trail Sport brakes, 1x11. 12.8Kg
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