Centering a rear drum brake

[shinyribs]

Copy and posted from another site:

I got this from RaceTech.com. I had them "arc" the rear brake on my Phaedrus projet, CB750K2. That is an old art of first turning the brake drum on a brake lathe. Then grinding the brake shoes to match the arc of the drum for maximum contact.

But to the subject of this post, anyone can center their brake plate when installing. You should tighten the axle only a bit. Then engage the brake either by hand or have someone step on the pedal. This will center the brake plate, taking up any of the slack clearance it may have between it and the axle. While the brake is engaged, tighten the axle.

If yours was off, this can improve the feel and power of the drum brake, reducing fade, and potential of glazing the shoe at a hot spot.

[TOOLS1]

Good tip. I learned something.
TOOLS

[shinyribs]

you did?!?! From me?!?!  I feel honoredI hope EVERYBODY sees this thread now!!! I'm mailing out fliers.....LOL!

[sgtslag]

That reminds me of my days in Electronic Technician school.  We had to build a circuit, and I knew the components were never as precise as the math, so there was always "slop" in the result.  We were supposed to build it, as specified by the calculations, then swap out resistors, until we got it exactly right...  I thought, "Screw that!  I'm not wasting that much time."  I put in a variable resistor, dialed into the exact resistance specified by my equations, and then I adjusted it, until I got the perfect result.  I measured the resistance of the pot, then I replaced it with a fixed resistor of that value, and called the teacher over to get signed off on it.

He complained to us, after I taught the entire class how to do it (it saved us a lot of time... and we had a lot of experiments to complete!), that he could see us all working for a company, with a vast array of variable resistors, dialing things in, to make a product.


He was just angry that we had figured out a way around his 'exercise'.  A company would love that technique, as it saves time, which is money, Baby!  Bike mechanics will love your technique -- they can get the job done faster, more efficiently, and more precisely!  Your technique is excellent!  Way to go, Shiny!

[mikefootusa]

Great solutions come with creative problem solving...loved both solutions!

[shinyribs]

I cant take credit for that solution. I just stumbled upon it and thought I would share.Hope it helps!

[LukeM]

Sgt, I applaud you for thinking outside the box. It's like the guy in body shop school who was superb at color matching.  Give him a paint chip and a body panel, and he'd make it match every time.  Found out later he'd mix up a batch of paint that was close, paint the panel, and then mask off and paint the chip he was given.  

Back in the day (very early 80s), my company was building a prototype switching power supply for a 25" computer monitor system.  We brought in this pseudo-genius circuit designer guy, who made up this closed feedback, highly resilient circuit, guaranteed to work first time.

So, believing the hype, they told him "Go build it."  
So he did.  The main switching transistor was a BU208.  They cost about $11 each in quantity.

He and I worked on it for days.  Switch it on, get it close to the voltage they wanted, and then *pop* the BU208 would fry. Switch out the control grid (resistor array in the feedback circuit) values, put in another BU208, fire it up again.

By the time the circuit was stable, we went through about 200 of those transistors. Plus labor.  Plus the designer's time and expenses.  I think I even asked him why he didn't put in a variable resistor in the control grid to dial it in. I was told "That's not how a real engineer does things".  Well, at that time, I was a technician: less concerned with why something doesn't work, more concerned with getting it working.

And now I'm an engineer, but I learned what to do and what not to do from that guy.
Luke M