Forum home› Road cycling forum› Workshop

Centre->Side pull brake conversion, bending rim

cerca1970cerca1970 Posts: 22
edited September 2009 in Workshop
Hi guys :D ,

I've just tried to fit a Dual pivot sidepull brake [tektro r556] on my old road bike which used to have weinnmann centrepull brakes on it. So far I've drilled out the back of the fork with a 5/16th drill bit to accomodate the recessed nut.

I set the brake up in the correct position with the recessed nut on the rear done up as tight as possible with an allen key.

The problem - Then I use the brake lever and the brake twists round causing one pad to contact before the other and so it bends the rim. Releasing the lever returns the brake to its original position + about halfway turned to the rim on the opposite side to where the cable is attatched.


Basically - I apply the brake and the mechanism twists around causing the rim to be grabbed more on one side than the other and so the rim bends each time the brake is applied.


Any help much appreciated - I don't have any experience with dual pivot sidepulls. :roll:

Posts

  • John.TJohn.T Posts: 3,698
    Either set the brake central before tightening the recessed nut or use the small allen screw on the top of the LH brake arm to trim the block position. Best to set the brake first and then fine tune with the screw. It also affects the modulation a bit.
    My Fleet.
  • cerca1970cerca1970 Posts: 22
    edited September 2009
    thanks for your reply

    the problem is that it is set up straight but when I operate the brake lever it twists the brake unit round. :?

    i've currently got outers covering about 1/2 of the cable on the front brake (cable stop on the headset) - does this make a difference?
    the instructions said something about sealant - do i need this?
  • redveeredvee Posts: 11,922
    Tighten the recessed nut up but not fully then pull the brake lever so that the calliper is on the rim the tighten up the recessed nut fully then adjust the fine tuning with the screw. Found this works better.
    I've added a signature to prove it is still possible.
  • John.TJohn.T Posts: 3,698
    The outers need to go all the way to the brake and not have a tight run to it either. If you are using the cable stops on the top tube for the rear brake the cable between them does not need outer.
    My Fleet.
  • cerca1970cerca1970 Posts: 22
    so only running the outers to the cable stop on the headset could be causing this? I was hoping it wouldn't be as I'll have to re-wrap the handlebar tape if it is...


    just to clarify, I'm only setting up the front brake atm
  • redveeredvee Posts: 11,922
    Upload some pics of the set-up.
    I've added a signature to prove it is still possible.
  • Barrie_GBarrie_G Posts: 479
    cerca1970 wrote:
    so only running the outers to the cable stop on the headset could be causing this? I was hoping it wouldn't be as I'll have to re-wrap the handlebar tape if it is...


    just to clarify, I'm only setting up the front brake atm

    this is most definitely your problem, side pull brakes work on a scissor action created by the outer and the inner being pulled towards each other at the side of the caliper, if you're stopping the outer at the headset it will never work and you run a real danger of not having enough braking power when you need it.
  • John.TJohn.T Posts: 3,698
    cerca1970 wrote:
    so only running the outers to the cable stop on the headset could be causing this? I was hoping it wouldn't be as I'll have to re-wrap the handlebar tape if it is...

    just to clarify, I'm only setting up the front brake atm
    It most certainly is causing it. You are likely to kill yourself if you ride it. You do not use the headset and seat stay cable stops at all with caliper brakes. Read the sections on Dual pivot brake service and Housing length here.
    http://www.parktool.com/repair/byregion.asp?catid=14&imageField2.x=26&imageField2.y=9
    Bookmark this http://www.parktool.com/repair/index.asp and this http://www.sheldonbrown.com/ for future reference before you do some harm.
    My Fleet.
  • cerca1970cerca1970 Posts: 22
    Extended the housing so it also runs from the headset cable stop to the brake

    The brake still rotates and causes the rim to bend (though I don't think it is as much as it did before). I'll post some pics later but I think this is one for the LBS :(

    -unless anyone has any other ideas...

    thanks for the links john t - sheldon brown has been invaluable for finding info on fixing up the rest of the bike over the past few months.
  • John.TJohn.T Posts: 3,698
    The extra housing is probably too short. It needs to have some free length to enable the top of the brake to move. You should really have one continuous length of housing. You should not be using the headset stop at all. You can get joining ferrules to connect 2 lengths of housing, useful as a last resort. I have some but am not sure where from. Try your LBS.
    My Fleet.
  • cerca1970cerca1970 Posts: 22
    Changing to one long length of outer for the front brake solved the problem.
    Thanks
  • The MechanicThe Mechanic Posts: 1,277
    I am all for people fettling their own bikes but this takes the biscuit. With so little knowledge you should leave this kind of job to the LBS before you kill yourself - and maybe others.
    I have only two things to say to that; Bo***cks
  • cerca1970cerca1970 Posts: 22
    The Mechanic wrote:
    I am all for people fettling their own bikes but this takes the biscuit. With so little knowledge you should leave this kind of job to the LBS before you kill yourself - and maybe others.

    Oh yeah thanks for sharing all your superior knowledge and helping me fix the problem - oh wait...you didn't

    moron.
  • The MechanicThe Mechanic Posts: 1,277
    Moron, that's good coming from you. I'm just trying to stop you from hurting yourself or others. You obviously haven't a clue about bikes so leave it to someone who has. Alternatively, get yourself on a cycle mechanics course rather than using step by step instructions on a forum. You don't even seem to be able to follow those instrictions.

    How you you react if some person ran you over in their can and it turned out that their DIY maintenance was the culprit.
    I have only two things to say to that; Bo***cks
  • laelae Posts: 555
    ^ oh leave him alone. He never said that he took it on the road with naff brakes, he just wanted to know how to put different brakes on his bike.
  • keef66keef66 Posts: 13,123
    A lot of people have no choice but to try and fix things themselves, and come on the forum for advice. No need to start a slanging match.
  • John.TJohn.T Posts: 3,698
    cerca1970 wrote:
    The Mechanic wrote:
    I am all for people fettling their own bikes but this takes the biscuit. With so little knowledge you should leave this kind of job to the LBS before you kill yourself - and maybe others.

    Oh yeah thanks for sharing all your superior knowledge and helping me fix the problem - oh wait...you didn't

    moron.
    Quite right. He didn't did he. Not much use as a mechanic then.
    My Fleet.
Sign In or Register to comment.