Tuesday, December 27, 2016

Give me a Brake

I'm excited about this post because it's been a long time in the making.

When I started this project over 2 years ago, some of the parts I purchased along the way were experimental. For example, I found a go-kart brake kit for an off-road go-kart called a Hammerhead, and the kit was affordable. I think I paid $80 for the entire thing, which included a master cylinder, a rotor, and a caliper with line attached. At the time I didn't really inspect it that thoroughly, and just assumed it was fairly standard as far as brakes and calipers go.
ZJ Brake Cylinder and Caliper (w/ my fabricated bracket)
 After installing my rear axle, with the ZJ rotor attached, everything seemed to be in order....But that was totally not the case. In fact the hub for the rotor was interfering with the caliper bracket which I had fabricated from some angle stock. It took a few dozen tries of attaching, grinding, re-attaching, re-grinding and fitting to make the caliper sit in a spot that would achieve any type of clamping force. But there simply was not enough contact between the rotor and the caliper. In the pic below you might see evidence of grinding and cutting the aluminum hub.
Bracket not so much...
Unfortunate choice of Rotor Hub
The rotor hub was a problem. It was originally intended for a totally different application (drive sprocket), so the section did not really work with the caliper bracket. In the pic below you can see how close the bracket was to the hub, and why it caused problems. As the brake rotor and hub spun, it had the unfortunate tendency to interfere with the shape of the caliper. A new solution was inevitable. Later I learned that these calipers are meant to be attached to an axle bracket, usually not much bigger than the axle itself.
Section of hub/rotor vs. caliper/bracket
It soon became evident that the brake system that in my mind would perform sufficiently, in design was the wrong application. So I took a step back to evaluate where I was and where I wanted to go. I was close to completing the functional parts of the chassis at this point so I was a bit frustrated, which was exactly why I needed to step back and take a broader look.
Not quite ready to test yet...
I retreated for a few weeks, and gave it some serious thought. Thats when I realized that the brake I scavenged from the Rotten Tuna was still in the spare parts box. I pulled it out, cleaned off the 2-years of grime that accumulated on it from sitting in my friends back yard, and not surprisingly it worked perfectly. But the compression ferrules were shot. I needed new ones - and the hardware store does not carry this particular type of cone-style ferrule with a flange, it's an aircraft grade part for AN-3 sized lines.
Ferrules...old vs. new
If you are not familiar with the ArmyNavy standard thread sizing have a look here:
More or less it's a brass 3/16" inside-diameter cone-ferrule with a compression flange.
Then I had the choice of using the traditional MCP nylon tube style lines, or doing something a bit upscale and choosing a braided line. I was able to find a 60" line from 'Allstar Performance' that did the job well (see pic below). Also in this pic is a new 8.25" MCP rotor, with a 4 point hub.
new parts
So there was a bracket that needed to be fabricated for the caliper which was a small project in itself, and then another bracket for the master-cylinder. For the Caliper I chose steel. I had some leftover angle iron...some cutting and welding and then had a bracket.
Steel Brake Caliper bracket in place
New Brake caliper and Rotor assembly
Then for the brake master cylinder bracket I didn't have much steel around but plenty of aluminum so I decided to try brazing. For small areas, that are not-structural, brazing works good on aluminum but I would not rely on it for anything that is a major structural part. Brazing Aluminum rods rely on a temperature of around 800ยบ on the surface of the metal to achieve phase change. The result is a strong bracket that is very light.
MCP master cylinder and DOT5 brake fluid
New brake pedal in position
One thing to mention here is the pedal itself. Usually go-kart pedals are attached to the master cylinder using an adjustable tie-rod, in case there are small adjustments needed. Since this is going to be a binary system, I decided to attach the pedal directly to the master cylinder. This meant that I had to use the same pivot for both the pedal and the rocker on the master-cylinder. It already has a good pivot, although small, so after making a larger hole it fit a 3/16" shoulder bolt easily.




Full view of Brake Assembly

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