🙄

For the sake of being helpful... below is a visual description of my my fix.

So, I woke up fresh this morning and decided that it would be as good a time as any to take a second look at those calipers and see if I could find a way to fix the issue. But first...

The Flaw

The actuating arm is made up of two halves: the outer, aluminum one, and the inner one, made of pressed sheet steel, which is an obvious cost-cutting measure:

https://cimg4.ibsrv.net/gimg/bikefor...8feef4a508.jpg

As you can see, the hex interfaces in each of the two halves of the actuating arm engage with the corresponding hexee in the rollers of the two pistons. However, while the outer half of the actuating arm has the hex molded into the alloy, which fits snugly on its corresponding piston roller with zero play, the inner half of the arm isn't so well made; with a hex-shaped hole simply punched into the sheet metal, the interface isn't even close to snug, which results in some play.

The Issue

That play between the hex hole punched into the sheet metal and the piston roller - however slight - will cause the roller to stay put and start moving only after the arm has traveled a few degrees into its arc. The result is that the inner piston will start moving later than the outer one, putting the two pistons out of sync.

Unlike a hydraulic caliper, where the piston that is met with the most resistance will stop advancing until hydraulic pressure has built up and equalized across all piston bores and all pistons will push the pads against the rotor with equal force and travel, the two pistons in a mechanical caliper move independently of each other and continue to move as long as the actuating arm is being pulled; neither piston will stop and wait for the other one to cover ab equal distance. So, when the two are out of sync, the one that starts moving first will also hit the rotor first, and still bend it into the other piston, just as a single-piston mechanical caliper does - which defeats the whole point of having a dual-piston caliper in the first place. So, in order to be able to center the caliper over the rotor probably and set equal pad-to-rotor clearanceson both sides, you need to ensure that both piston move an equal amount at exact the same time.

The Fix

In order to achieve this, I had to make sure that the inner half of the actuating arm fits snugly around the hex of its piston roller. Here in the third world, we have a philosophy: to solve a complex engineering problem, simple tools and brute force usually will do the trick! :D

So, I put the inner half of the actuating arm in my small table vice and squeezed...

https://cimg4.ibsrv.net/gimg/bikefor...d0177c4902.jpg

​​​​​​... just enough to slightly deform the hole and ensure a snug, tight fit:

https://cimg4.ibsrv.net/gimg/bikefor...4377a004b9.jpg
Before...

https://cimg5.ibsrv.net/gimg/bikefor...927a3ed034.jpg
... and after.

I realized that I had been a little overzealous with the squeezing of the vice, which required me to enlist the services of my dead blow hammer to get the thing to press itself onto the hex, so I was careful not to squeeze as hard for the other caliper. This is tricky because, unlike the outer piston roller, which has an ample amount of material for the actuating arm to engage, the hex of the inner roller is a very slight nub that's barely the thickness of the arm's sheet metal, so proper engagement is critical for this to work:

https://cimg4.ibsrv.net/gimg/bikefor...caeee1375d.jpg
Inner roller
https://cimg6.ibsrv.net/gimg/bikefor...4401cf4172.jpg
Outer roller

And voila! With the play between the inner half of the actuating arm and the roller of the inner piston eliminated, now both pads move an equal amount at the same time! I'm from the Third World, where we take things that aren't even supposed to work and make them work! 😁

I have no idea what I'm looking at (being a tried-and-true rim-brake guy), but the pictures are nice and clear, and I'm glad it got worked out!

😩 Well then you might find this interesting.

Hey, they seem to work well. Actually, I spend most of my time with this type of rim brake:

https://cimg8.ibsrv.net/gimg/bikefor...b8cae9d796.jpg

🤔 Well then you might find this interesting

:lol:

A summary of this thread so far...

* * * * *

sjanzeir: "Do not waste your money on junk like this!"

Also sjanzeir: I never said they were bad.

Bike forums: What?

sjanzeir: They're just hard to set up. I didn't even ride them, so I have no way of knowing if they're any good. I only bought them because free shipping.

BF: ???

sjanzeir: Oh, sure! New guy attacking me just because I live in the middle east! Why is everyone making false assumptions about me? Grrrr!

BF: Calm down, and let's be clear about this.

sjanzeir: Okay, I worked on the brakes some more, and now they seem fine.

* * * * *

OP, I'm glad you got them sorted, and I hope they work well for you. I don't make personal judgements based on whether you're living in the third world or born with a silver spoon in your mouth, nor on how many posts you've written on the forum. I just think this thread took kind of a bizarre course. Maybe it can turn into a productive discussion after all.

https://cimg1.ibsrv.net/gimg/bikefor...1c463aede7.jpg

Wow! You're the diametrical opposite of me! :D

Apparently so, in our self-assessments at least. :thumb:

Yeah, I could work with you on that.

By the way, it's probably going to be a while before I put them back onto the bike and take them out for a test ride. For at least the next few days, I'm going to be testing out my old hydraulic Shimanos. Lucky for me, my Hemingway has all-external cable routing, so swapping out entire braking systems - including the rotors - takes 10 minutes!

what’s this thread about ?

Bad things.

All threads devolve into chest thumping. This one went there quicker than most.

Why would you skimp on brakes and buy some cheap no name junk instead of buying brakes from reputable manufacturers such as Shimano, Sram and Tektro ?

Well if it ain't the Child of the Wolves himself! You're a little late to the party, aren't ya? I was kinda worried that you'd show up with a question like that! I hope it's a rhetorical one! 😁

Guess we really have come full circle!

I would like to know how they are with actual testing of they stop a bike now that the issue with excess play has been fixed as compared to the ones you actually used. I am sure you are not the only one that had this issue and the possible "fix" could be beneficial to someone else.

I'll report back with objective seat-of-the-pants data as soon as I have some! Of course, I won't be comparing apples to oranges and pitting them against my four-piston hydraulic Shimanos, but rather red to green apples comparing them with, say, the outstanding Meroca single-piston calipers , the troublesome WinZip floating calipers, or the original, unbranded factory BB5 calipers (those could've been more than adequate with the right kind of pads, but sometimes it's better to be a tyro who's willing to learn abd try new things than to be blissfully satisfied with mediocrity. No regrets.)