Cable brake questions

[Jamie P]

I have a few questions for the group. I talked to someone at BMI before buying this setup because I wanted to be sure the components I bought would play well together. I'm not so sure they do, but before I spend a ton of time reinventing the wheel I'd like to see how others have done this.

The first photo shows the sloppy fit between the hand brake and the cable. For the purpose of demonstration I pushed on the cable to show how much side-to-side movement there can be. Is there a way to hold the cable a little tighter in its connection to the handle?

At the other end I've got a bare cable and the arm of a mechanical disk brake. What is the best way to secure the end of the cable housing? I know I'll have to fabricate a bracket to support it in position, but how should I secure the cable from sliding out of the bracket?

For the connection to the brake arm, BMI suggested the clevis shown in the third photo with a wire clamp inside it. Now that I have the parts in my hand the concept feels a little hokey. The clevis is meant to thread onto a rod, not to have a cable fished through it. Maybe I'm wrong, and the concept is fine.

I feel like the more secure I can get all these parts the better this will perform. Any thoughts or photos of what you've done?

 

[Hellion]

Is there a way to hold the cable a little tighter in its connection to the handle?

Photo #1: The brake lever is meant to accommodate a much larger cable/cable sheath. You could look for a larger one but I have seen all kinds of wobble on production bikes, minibikes, etc... Some of the sloppiness will go away when the brake cable is attached to the other end and you take up most of the slack, accounting for a little free-play as needed.

To take up the wobble at the hand brake, some sort of ferrule is needed. The easiest thing I can think of is probably K&S metal. They make tubing that small usually in aluminum, brass or steel. I think Ace Hardware carries it as well as most good hobby shops like HobbyTown.

As for the rest, I can think of doing it the Bubba way with some cable crimps and such, but I don't like doing it that way.

 

[Jamie P]

Photo #1: The brake lever is meant to accommodate a much larger cable/cable sheath. You could look for a larger one but I have seen all kinds of wobble on production bikes, minibikes, etc... Some of the sloppiness will go away when the brake cable is attached to the other end and you take up most of the slack, accounting for a little free-play as needed.

To take up the wobble at the hand brake, some sort of ferrule is needed. The easiest thing I can think of is probably K&S metal. They make tubing that small usually in aluminum, brass or steel. I think Ace Hardware carries it as well as most good hobby shops like HobbyTown.

As for the rest, I can think of doing it the Bubba way with some cable crimps and such, but I don't like doing it that way.

Thank you, Hellion.

 

[Hellion]

Still ruminating on solutions....

I need photos of my Baja Warrior 200 or any drum brake (I'll have to go examine it). The brake cable has a very secure clevis pin on the end that is threaded for fine tuning. Found this product photo:



That's a nice brake cable, has a rigid section with a rubber accordion boot on the brake side. Pic shows how it interfaces with the clevis fork(?) at the brake. That's what I would emulate. You just need some kind of cable holder/bracket.

 

[Jamie P]

Just to close the loop on this... for now... I've added a couple photos. The first shows how I corrected the sloppy fit of the cable housing in the brake lever. I cut off a bolt, drilled a small hole all the way through it for the cable and a larger hole half-way through for the housing. Now it's a tight fit.

The second photo shows the back end of the cable. Obviously the zip tie is temporary. Everything moves well and seems to function, but it doesn't seem to have much grabbing force.

This weekend I'll test it out. If it feels like a little more leverage will make it into a good brake then I'll extend the mechanical brake arm, and I'll move the cable attachment further down. If it doesn't feel like more leverage will help then I'll change course and build a foot brake. I'm trying to avoid that for all the added work, and I was trying to keep all the controls at my hands.

 

[Whitetrashrocker]

Nice solution.

 

[Hellion]

Is that a cable stop on the cable that is captured inside the clevis fork?

 

[Jamie P]

Is that a cable stop on the cable that is captured inside the clevis fork?

Yes. If the brake works well I'll back it up with a second cable stop.

 

[Jamie P]

I figured I should follow up on this post in case somebody looks at it in the future. I ran the go kart on its first phase of testing last weekend. The brakes totally suck. I think friction in the tires and powertrain slows it down more than the brakes do.

It seemed like it should function well, but no sir. Now it's back to the drawing board on the brake system. I've owned several Manco karts in the past, and they stopped very well with band brakes, so I'm leaning in that direction. However, I'm tired of spending money on things twice with this kart, so I experimented with what I have last night before I give up on it.

I gathered some crap from the shed and stuck it together in order to make a demonstration of force required to stop the kart. With 25 lb of force applied it takes some work to rotate the rear axle by hand, but it's not difficult. It would take an unacceptable distance to stop with that force.

I got the weight up to 45 lb, and I could still rotate the axle by hand. Nobody I know can squeeze a brake lever with more than 45 lb of force. I could switch from a hand brake to a foot brake, but I'm not confident that will work either. It obviously will never lock up the wheels if I can rotate it by hand.

Are these mechanical brakes just a crappy design, or am I missing something? If this is how they are supposed to work I feel like nobody would ever choose to use this technology.

 

[Functional Artist]

How close are the brake pads to the rotor, when not being applied?

It should be just a hair (technical term for very small gap)

If the "gap" is more/larger than ~1/8"
...it takes most of the "range" of the caliper
...just to get the pad to the rotor
...before any actual "stopping force" can be applied

Is there any brake pad to rotor adjustability, on the caliper?

 

[Hellion]

Are these mechanical brakes just a crappy design, or am I missing something?

The glaring issue you might be having: you must adjust this brake caliper like an automotive-type disc brake. In other words, the pads should be lightly dragging on the disc/rotor.

I think Airheart / Tolomatic was the original manufacturer for these so that is where I got this info. The install/adjust procedure is simply #2 at top left; Adjuster Pin 8 and Jam Nut 9.



I am going off memory on how good (or how bad) these brakes are. I think @Whitetrashrocker uses this type of brake on the daily almost, has no issues with it and can advise further. These are common, common brakes and they've been around a long time.

 

[Jamie P]

I have them adjusted so the pads barely touch the rotor all the time, and the lever can move about 1/2" before force starts to apply. Then with full force applied the lever moves maybe another 1/2". It's nowhere near bottoming out against the cast body of the caliper.

It doesn't help that the rotor is slightly warped. Other than making a little friction sound with every rotation it doesn't seem to be a problem. It sucks that a brand new rotor arrived warped, and my brand new sprocket is out of round. Plus the cable falls off my twist grip. Plus my seat is falling apart after 5 minutes. It's hard to find good stuff.

OK. I'm done complaining now!

 

[Hellion]

I have them adjusted so the pads barely touch the rotor all the time

Adjust them per the instructions I posted and then report back. A rod is better than a cable, at least I think so. Stranded cable seems too elastic, like using a rubber band.

 

[Jamie P]

Hellion, I followed the instructions you gave. It ended up adjusted almost exactly as I had done it by feel, but it is nice to know that it's set up correctly. The results were the same. With a 25-lb pull it was pretty easy to turn the wheels. With a 45-lb pull it was difficult, but I could still do it. It wouldn't be able to lock up the tires, but it would slow the kart down somewhat, I suspect.

As a test I extended the arm on the brake by 1.5". There is no reason for this length other than the scrap of steel I have was that size, and any longer would start to be a clearance issue. With a 45-lb pull and an extended lever it works pretty well. The problem is that's a lot of force to produce by just your calf muscle in a seated position. 25 lb with an extended lever still didn't cut it.

I'm wondering if the rotor is just too small. It came as a live-axle kit, so I didn't think about it, but a 6" rotor is pretty small for a heavy kart and an adult rider.

So, now the big question is do I buy a bigger rotor, reconstruct the whole thing, and keep my fingers crossed, or do I buy a band brake?

 

[Master Hack]

6 inch rotor aint much. Mechanical also. Double wammy.
stretchy cable, thats 3 wammys. my $.02 bigger is mo bedder.

Is this 2x6 square tubing? 2x4? can't tell from here. either way, ya think that's gonna be strong enough?
Holy crap dude, that's Purdy stout! what's this sukka weigh?

I have a hydraulic M/C and caliper off a crotch rocket. I don't have much use for, PM me if ya might be interested.
I don't want a lot of dough for it....

 

[Master Hack]

It should be just a hair (technical term for very small gap

Thats purdy vague, i think there are different types off hair with difference thicknesses. Like feeler gauges. Can you be more specific.?

 

[Master Hack]

 

[ezcome-ezgo]

25-45 lbs isn't that much. You also have to consider the leverage gained at the lever or pedal. The diagram below generally indicates mechanical advantages gained from leverage. If your foot could apply 45lbs of force to the pedal (and it could) you could be producing up to 112lbs of net force to the cable or rod. Or maybe I should shut up and keep quiet.

 

[Jamie P]

6 inch rotor aint much. Mechanical also. Double wammy.
stretchy cable, thats 3 wammys. my $.02 bigger is mo bedder.

Is this 2x6 square tubing? 2x4? can't tell from here. either way, ya think that's gonna be strong enough?
Holy crap dude, that's Purdy stout! what's this sukka weigh?

I have a hydraulic M/C and caliper off a crotch rocket. I don't have much use for, PM me if ya might be interested.
I don't want a lot of dough for it....

Yeah, it's got a lot going against it...

It's an overbuilt frame for certain. The reason is not for strength. It's a replica of a 1932 Ford frame, which has a very specific appearance. In other words, it's built like that for looks.

 

[Jamie P]

25-45 lbs isn't that much. You also have to consider the leverage gained at the lever or pedal. The diagram below generally indicates mechanical advantages gained from leverage. If your foot could apply 45lbs of force to the pedal (and it could) you could be producing up to 112lbs of net force to the cable or rod. Or maybe I should shut up and keep quiet.

View attachment 161130

This is great. I forgot about the basics because I've felt flustered lately.

If I use mechanical advantage like your sketch I should have plenty of force from a foot pedal. Thanks!