A Different Kind of Disc Brake: 1949 Chrysler (2023)
macsmotorcitygarage.com
macsmotorcitygarage.com
I wonder what prevented this camming innovation from being transferred to the more conventional drum brake of the time?
I'm not an engineer, but I do have some wrenching hours under my belt. I see a flaw in the design: The two halves of the drum are held together by machine screws/bolts. The braking pressure from the pads is applied directly to these screws. If they are not properly fastened, or if they are loosening over time, then braking force will be directly impacted. A failure could result in a total loss of braking ability. A conventional drum or disk brake is kind of fail safe in that regard: The mechanical pressure from the brake pads is not transferred through any fasteners. I see this design less resistant to poor maintenance practice. Maybe they somehow accounted for this and the article failed to mention it.
Some motorcycles even twin leading shoes on the front (maybe even four leading shoes with two sided drum brakes). These had issues with modulation like the Pederson brakes. You also had twin trailing shoes when backing up, so you had to squeeze the brakes extra hard then.
A slight nitpick, the torque applied to the caliper from the disc, through the pads, does travel through the caliper mounting bolts. It's a lateral force rather then a axial one but it does go through fasteners.
This wikipedia photo happens to be from an AMC pacer, but it does show the frame that takes the braking torque load (https://en.wikipedia.org/wiki/File:Detail_of_-_AMC_Pacer_-_r...). The frame is the lighter metal object at the top above the top edge of one of the pads.
Unfortunately for America, Europe's scarcity cars were not fit for her market, so Detroit had very little competition. They also had no resource constraints. Once certain dimensions of consumer preference settled, Detroit coasted.
Europe and Japan were poor, so they had to work to make good cars. They were also culturally open to each other.
Then, one day in the 90s, Detroit woke up dead.
https://www.hotcars.com/how-japanese-car-manufacturers-invad...
EDIT: Another question I wasn't able to figure out from their brochure is how they integrate with the factory front disc brakes.. Like, is there some kind of balance control?
In that case the ball and ramp are in the caliper attached to the frame. I don't think they're self-energizing in that application; the balls aren't all traveling in the direction the rotor is.
I'd say they're at least 85% as good as hydraulic disc brakes while being 1% of the hassle to maintain.
1. The knowledge of how to deal with hydraulics across the industry is slowly accumulating. We've been fixing bikes with bowden cables for a hundred years give or take a bit. We've been dealing with hydraulics for 25 years give or take a few, and it's a really recent development that they've trickled down to the low end of the market and penetrated the road market at all. The knowledge of how to fix them is not as widespread as you'd think.
2. Compounding the above, we have two competing systems (naturally). SRAM runs DOT fluid and Shimano runs mineral oil. The bleeding procedures are different (naturally). Surprisingly, the hygroscopic nature of DOT fluid is a non-issue. Both systems run hard for a year are basically due for a fluid change.
2.5. Some of the bleed procedures are consistent within a manufacturer's line over time. Often times they are not. Step one of a bleed is usually RTFM because the brakes you're looking at are probably different from the last three sets you've done.
3. Everything is small. The entire master cylinder assembly has to fit inside the brake lever. On a road bike, your hand wraps around all of that, plus the shift mechanism. Access to the reservoir cap, which is also the bleed port is about as good as they can make it, but it's still one more damn thing to peel back the rubber hood.
4. The calipers are similarly small, leaving less room for sealing, etc.
5. There's little room for manufacturing variation in the mounts as well. In theory this would affect mechanical disc brakes as well. In practice, they hold up better when the caliper is mounted cockeyed. Park Tool makes an extremely elaborate facing kit to rectify problems with mounts. The shop I work at part-time has one, and I've had to use it. The fact that the rotor is non-rigid does buy you some tolerance back, but sometimes it isn't enough.
All of the above adds up to a lot more hassle than mechanical disc brakes not because it's insurmountably hard to do the work. The major factor is that a good set of mechanicals is so damn simple and reliable. The set on my mountain bike has 7000 miles of touring, plus mountain biking, and I doubt I've spent cumulatively 3 hours working on them.
1. Despite being relatively new, bicycle hydraulic brakes are dead simple. There isn't much to learn, unlike the switch to discs which was a much bigger change. You also don't really need to fix them when a pre-bled set of Shimano MT-200 brakes is 25$, in case you find yourself with a hairy problem a bleed won't fix.
2.1 The industry is converging on mineral oil, as SRAM now has mineral oil brakes. Also, their hygroscopic nature actually is a problem: good quality mineral oil brakes last years between bleeding, which is rare for DOT fluid.
2.2 Mineral oil bicycle hydraulic brakes are very different from hydraulic oil on cars or some bikes - it's a sealed hydrophobic system. You don't need to bleed them unless there is a leak or dirt gets past the seal, and if you don't the worst that happens is that they gradually get mushy.
Meanwhile, if you don't bleed motorcycle or car brakes you can very suddenly lose braking power when you need it, for an unwisely designed sealed DOT system your brake line can literally burst open. But that's not a problem with modern good quality mineral oil hydraulic brakes.
2.3 This is a SRAM problem. Shimano hydraulic brakes are bled almost identically, and though doing a full flush changes a bit every now and then the change is always very minor (and you rarely need to do a full flush)
3. Things don't need to be big. You're not going to be messing with the master cylinder realistically speaking. Also on the most widespread hydraulic brakes there is no rubber hood around the bleed port, just screws that have o-rings around them.
4. The calipers aren't small at all. Look at top of the line weight weenie road bike calipers to see what an actually small caliper is. Common mountain bike calipers are not especially limited by size, they just don't need to be bigger than they are. In mountain bikes they get bigger if you pay more.
5. This is completely false. 2-piston or better yet 4-piston hydraulic calipers, along with convex-concave washers (this is very very important) offer by far the most flexibility as to mount facing. You can easily trick yourself into thinking that mechanical disc brakes are better due one of the pads being rigid and easy to offset as to accommodate a skewed rotor: this almost always backfires hard down the road once the pads start to wear askew. Also, for extreme cases we have floating rotors. The big thing though is to use concave/convex washers: after doing that I've often had bikes that just wouldn't work right with mechanical calipers work perfectly with cheap hydraulic calipers, I'm talking about a good 5 degrees out of alignment on the mounts in the pitch/roll axis.
I've put 9000 miles on my bike and I've only bled it once in 4 years. I haven't had to do any hydraulic specific maintenance at all, the most time I've spent was changing pads, changing/truing rotors, and aligning my calipers (often while waiting for my concave convex washers to come, after which it took all of 2 minutes and a business card).
https://www.fcpeuro.com/blog/reinventing-the-rotor-audis-ufo...
It looks as if it may have had some weird dynamics also, that would be confusing to a driver used to regular brakes.
Was there a post-war complication trend in engineering?