Feeble calliper brakes on child's bike

[eBiker]

I bought a used, 18 inch aluminium wheeled bike for my 7 year old granddaughter.
The brakes were useless, so I replaced the blocks with new Raleigh brand and replaced both brake cables (outers and inners), lubricating the inners during installation. The cable runs have no excessively tight curves. I also slackened, lubricated and re-tightened the calliper assemblies which move freely. I cleaned the rims using Scotchbrite and then wiped them clean with isopropanol.
All of this made little difference. I was able to lock the wheels by applying extreme force on the levers, but my granddaughter was unable to exert sufficient force to control her speed on a moderate downhill slope. She is able to operate the brakes perfectly well on two other bikes.
I then fitted Kool Stop Continental Salmon brake blocks. These perform better, but still require an inordinate degree of force and squeal terribly. I have tried setting them with toe-in, toe-out and parallel to the rims but these adjustments appear to have no effect on force required or squeal.
I have noticed that both brakes are very much more effective when wheeling the bike backwards than forwards.
I am at a loss to understand what is going wrong with these simple mechanisms.
Any suggestions?

[gaz]

Children finding it difficult to operate the brakes on childrens' bikes, due to issues of either the reach or the strength required to operate the lever are sadly too common. Reach is sometimes adjustable, although this may bring other problems if the lever then reaches the bar too soon.

There is also the possibility, particularly if either the callipers or the levers are not original, that they are not designed for each other, e.g. V-brake levers will be a poor match with calliper brakes.

[gregoryoftours]

Post some photos of the brakes. If they are cheap stamped steel and long reach they will flex like hell and provide weak leverage.

[eBiker]

Reach is adjustable, so not a problem. I suspect the callipers are original or at least suitable as they look right and there are no mounts for V brakes. The levers look similar to those on a similar bike which she can use without a problem - perhaps I should do a close comparison of geometries.

[Tigerbiten]

If you have the old brakes and if they fit the new bike, you could try swapping them over and seeing if it makes a difference.
If they do then the new brakes are bad, if they don't then something is off with the new bike.

[PT1029]

A couple of points, well 3 actually.
Quite a few small kids bikes have side pull calipers with the pads at the bottom of the brake arms. These will have a low mechanical advantage, and so will always give poor braking. If you are able to replace the calipers with longer reach ones, the pads will then need to be further up from the bottom of the new brakes, so providing better mechanical advantage. Whether this would make a noticable difference or not I don't know.
You say the brakes work better wheeling the bike backwards. Check the pads are toed in correctly (front end hits the rim 1st). The pad probably don't have toeing in adjustment, so you most likely will need to bent the brake arms to do this. Carefully if alloy brakes, a bit more care free if steel brakes!
Oh yes, 3rd thing. Check the levers are not designed for V brakes - usually this is not the case on small bikes (but I have seen this on adult bikes, some times on makes that you'd have thought would know better!)

[Vorpal]

Kids bikes are often treated roughly. I found when teaching Bikeability, that levers that were the hardest to do were often bent, rusty, or slightly damaged. If it were my kids, bike, I would take a close loke at the levers, and maybe swap those from another bike.

The points about the side pull calipers as above are also good. The other thing is that the noodles on kids bikes are often cheap & cheerful chunks of steel that rust rust inside quickly, and can produce considerable ineffciency.

[Brucey]

Reach is adjustable, so not a problem. I suspect the callipers are original or at least suitable as they look right and there are no mounts for V brakes. The levers look similar to those on a similar bike which she can use without a problem - perhaps I should do a close comparison of geometries.

I'd be suspicious that someone has paired V brake levers with ordinary side pull calipers. The calipers will likely be poor with any levers but with V-levers they will be especially pathetic.

cheers

[bertgrower]

What are the brakes and levers made off?

[eBiker]

Many thanks for all replies.

Brake lever

Cable run

Calliper front

Calliper side

PT1029:
With long-reach callipers the pivot to pad distance would be the same, so wouldn't the mechanical advantage be the same?
I have tried the pads toed in, toed out and parallel to the rims. In each case the brakes work better backwards, and squeal in both directions.
I'm not sure how to identify calliper vs V brake levers.
Vorpal:
The levers are free moving. There are no noodles to rust.
Bertgrower:
The callipers are steel. The levers are of very rigid plastic and do not contact the bar under the maximum force that I can exert.

[tim_f]

I'm not sure how to identify calliper vs V brake levers.

This article http://www.parktool.com/blog/repair-help/travel-agent-installation-and-adjustment#article-section-1 gives a guide to identify the type of brake lever.

[alexnharvey]

You are attempting to polish a turd.

Those calipers are lousy facsimiles of real brakes. I see similar on the bike shaped objects well meaning friends and family insist on liberating from skips and recycling centres for my nephews. I doubt they're mismatched levers, just crap calipers. Why's there no law on the effectiveness of brakes!

You'd probably spend more than the whole bike is worth getting a decent caliper.

I baulked at the price of islabikes, frogbikes and similar, but given the residuals they end up being less expensive than buying cheap bikes which you can only give away or dump.

[Brucey]

the brake lever appears to have the Mechanical Advantage (MA) of a V brake lever (about 2:1), but the cable pull of a side-pull lever, because the levers are meant to be worked by a child. Really the handlebars should be a smaller diameter for nippers, and the levers ought to have an MA of about 4:1.

The brake calipers appear to have an MA of less than 1:1 (in other words the reach is longer than the arms from the centre bolt to the pinch bolt) which gives an overall system MA of about 1.75:1. This is about half that of most brakes that folk find acceptable. In addition the quality of the parts is poor.

The first suggestion I can make that will improve matters easily is to move the levers inboard a bit; this will allow the child to use their strongest fingers nearest the end of the brake levers, which will generate the most force.

The second suggestion I would make is to get some different brake levers. Ideally you need some levers with a MA of about 4:1. These will be tricky to set up ( the running clearance of the brake will be about half as much) but the brake power will be doubled vs what you have now. These levers will probably be longer and the distance from the cable to the fulcrum will be reduced as well.

The third suggestion is that you could perhaps fit calipers lower down (which will have a higher MA) by using drop bolts or similar.

cheers

[531colin]

If you have the time, skills and inclination, get a scrap bike with Vee brakes and braze the vee brake fittings onto that frame.
I suspect a bike with an Ashtabula bottom bracket, and brakes made out of pressed baked bean tins, will have poor wheels with nasty pressed steel hubs and a very heavy frame, and any actual money you spend on it will be a dead loss.

[PT1029]

"With long-reach calipers the pivot to pad distance would be the same, so wouldn't the mechanical advantage be the same?"
The brake pad depth would indeed be the same. But a deeper caliper would also be wider at the top (bigger cable - arm pivot distance), so the leverage would be greater.
That said, you might struggle to find a deeper caliper than the one you already have.

Also the brake lever (but not housing) looks like its plastic, so probably will flex when pulled, so losing braking power. Finding some similar but metal levers might make a bit of difference, but probably still be quite poor.
I agree with the various comments about economically not worth doing for little gain.