V brake modulation

[summerdays]

I'm trying to help a friend with her child's bike. Less than 6 months old and hardly ridden, not been ridden in the rain probably only done a couple of miles and still looking shiny. One brake works fine, the other is on or off with nothing in between. If I remember correctly I think it's the rear brake. What do I need to do to introduce a little bit of modulation in there?

 

[yadder]

So right hand this a rear brake, left hand front! Set V-brake not difficult.
Pads should be running in parallel and running in parallel to the radius of the rim brake track.
The distance between the shoe and the rim not less than 2-3 mm and not more than 4-5mm.
For beginners this is achieved , you can relax the bolts pads , press the knob and tighten the bolts , checking the position relative to the rim

 

[summerdays]

So it's the distance to the rim that gives the modulation?

 

[Globalti]

Not quite sure what you mean. My understanding of modulation is the progressive effect that you get from squeezing the lever harder. Is that what you mean?

 

[summerdays]

Not quite sure what you mean. My understanding of modulation is the progressive effect that you get from squeezing the lever harder. Is that what you mean?

Yes - the (I think it was the rear brake.... I can't remember now), is just either fully on, bike stopped or no effect at all, so you can't use it to slow the bike. (Well slight exaggeration but so that you understand what I mean). The other brake allows the slowing of the bike with gentle pressure.

 

[LetMeEatCake]

So it's the distance to the rim that gives the modulation?

My understanding of modulation is the progressive effect that you get from squeezing the lever harder.

Pad distance to the rim alone won't necessarily sort your problem, but you won't get good modulation without correct pad placement, so it's a good place to start. For example if the pad butts into the tyre when the brake levers are pressed, your modulation will not be good!

 

[summerdays]

Pretty certain the pads looked ok but I'm seeing my friend tomorrow for lunch so I'll have a peek then.

 

[raleighnut]

So right hand this a rear brake, left hand front! Set V-brake not difficult.
Pads should be running in parallel and running in parallel to the radius of the rim brake track.
The distance between the shoe and the rim not less than 2-3 mm and not more than 4-5mm.
For beginners this is achieved , you can relax the bolts pads , press the knob and tighten the bolts , checking the position relative to the rim

No you are wrong in Great Britain the brakes are always right hand front brake due to us riding on the left hand side of the road. Also the pads should have 1mm (or so) of toe in to prevent grab and squeal (please note these are V brakes and not cantilever which can be adjusted by pushing on the pad holder stem) so the adjustment is by either:

1. moving the 2 mating washers around (1 pair are thick, one thinner)
2. Releasing the cable clamp bolt and pulling more cable through then re-tightening.

To achieve the proper degree of 'toe in' place a 1mm thick piece of card at the back of the pad and pull on the brake lever before tightening the retaining bolt up.

 

[Pat "5mph"]

@summerdays it could be you need to fit a new cable.
I had this problem on inspecting a kid's bike before a ride: the mechanic ( borrowed bikes from a cycling project) said it needed a new cable, he found out the fitted one was a gear not a brake cable.
Cable changed, all well.

 

[lpretro1]

Grease brake mount studs too - one arm may be sticking on

 

[fossyant]

If the pad isn't sticking on the tyre (common issue), then I'd personally pull them both off and clean out and spray liberally with GT85, then wipe and apply grease.

The only issue is if they are really crap cheap brakes, you may be fighting a losing battle. New cables are often a good option - my daghter's NEW Carrera had poor disc brake operation. The cable had corroded slightly inside the outers prior to delivery. Simple cheap fix for me, but shouldn't happen. The front mech that was fitted was also a cheapo no-name thing, despite everything else being SRAM 3 or 4. Replaced with a SRAM 3 front mech for less than a tenner.

 

[Globalti]

If the brake is grabbing on, there's something wrong with the setup, which is causing the pads to pull in.

 

[shouldbeinbed]

Just with the pads: A good clean and dismantle, grease and properly set cable & be sure that the blocks washers are both constructed right might be enough but I suspect not.

Definitely toe the pads in.

Depending on how thorough you wish to be, you could remove the V arms to be sure the inner coiled spring is in the appropriate frame lug holes on each side, also that the spring bar that runs up the brake is correctly seated and consider the adjustment of the grub screws at the bottom of the V arm that manages this spring bar tension.

It could be something misaligned or loose in the basic set up that is holding one pad to the rim by the force of the other's stronger or better gapped springs inclination to pull the V arm off the wheel. If the cable is set tight it would be aa v quick grab on the other side too.

Cable sticking in the outer? remove cable chedk.for minor kinks that would need a new cable immediately & check the outer too for damage. If not kinked then lightly sand the cable and run oil down the outer to ease it.


Unlikely option, check that there isn't something external fouling the free movement of a/both brake arms. Rack badly sited..... I had a cheapo plastic set of mudguards that had a slide on attachment bump just bulky enough the catch the cable guide arm on the top and make rear braking a mystery experience.

 

[Milkfloat]

I am confused - the OP is not talking about sticky or rubbing brakes it is poor modulation - i.e. brakes are either too good or not on. Most people seem to be giving advice for brakes sticking on or pushing on one side only.

To me, I think the first thing to try is to toe in the pads a bit more - that way the pad partially touches the rim with the first bit off pull and progressively gets more pad contact as the pull continues. If that fails - maybe time to buy some crap pads, I have loads!

Am I missing something?

 

[summerdays]

I'm fairly certain the brake doesn't rub as that would be something I would spot fairly easily (not absolutely sure as I only had a quick look at it when I bumped into her last week), I'll have a bit more of a look at lunch today.