Looking for a HIGH friction lubricant

fyrstormer

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silicone oil has a flashpoint and ignition temperature... it burns.

It has a very HIGH ignition temperature and excellent thermal stability which makes it a good candidate for a brake lube. And the purpose of grease is exactly that it allows re-flow.

but in itself silicone oil isn't a good lubricant for steel on steel lubrication, hence the powdered additives imo.
Silicone oil doesn't dissolve in petroleum distillates. Roller brake "grease" dissolves instantly in petroleum distillates. Why are we still arguing about this? It's not silicone oil. I have lots of silicone oils for other hobbies and I'm very familiar with their properties.

Your point is taken regarding bentonite-thickened oil to make grease, however. I wasn't aware that was actually considered "grease", and I don't know why it would be, but if that's what the professionals say then I have to accept it.
 
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Never heard of these brakes and I had to look them up. One piece of information I picked up from the Sheldon Brown website is that once the friction surfaces are damaged, no matter what you do, the brakes lose stopping power and need to be replaced. At this point you might be ahead by just buying new brakes.
 

fyrstormer

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The documentation on roller brakes (including SheldonBrown.com) assume you don't disassemble them to modify them -- because you're not supposed to. Roller brakes aren't idiotproof like the simple rubber caliper brakes that came on bikes when we were kids, and thus aren't designed to be disassembled, but it's not difficult to do as long as you're careful and pay attention. I modified mine years ago to be easily disassembled for inspection, cleaning, and servicing. The only tricky part is making sure the rollers don't get tilted when the two halves of the brake are reassembled.

Having been able to examine the internal parts, the friction surfaces (or the parts actually contacting each other, anyway -- the brake shoes haven't fully bedded-in yet) are mirror-smooth. There is no damage. As far as I can tell, the braking force started decreasing as the brake shoes started bedding-in because there was more contacting surface area to maintain a stable lubricant film, preventing direct contact between the friction surfaces. While that may be ideal from a lubrication perspective, it's far less than ideal from a braking perspective.

Since I last posted here, I took some inspiration from the MSDS for the roller brake "grease" (I still dispute the usage of the word "grease" to describe any lubricant that isn't soap-thickened) and made my own "grease" using light machine oil and diamond powder. The original grease contains silica powder (aka engineering-grade sand), which was added as an abrasive that could reach through the oil film to directly contact the friction surfaces, so I decided to try an abrasive that wouldn't be worn-down by the steel brake shoes and brake drum.

Now I'm able to skid the rear wheel reliably (which is the most braking force the bike can actually make use of), and the friction surfaces are still mirror-smooth. I'm sure the more aggressive abrasive will wear-down the friction surfaces faster, but that's a reasonable tradeoff because the friction surfaces are made of steel and will last a very long time anyway. Bicycle commuters in Europe have routinely gotten more than a decade of service from a single set of roller brakes, despite having no user-serviceable parts.

If I start to notice any damage on the friction surfaces, I can always add a little MoS2 powder, which was also used in the original grease and I've used to great effect in other applications. Copper powder is also an option since it does a nice job of smearing and filling in microscopic holes (and is also useful for maintaining electrical conductivity between electrically-charged threads that require lubrication), but for the time being I see no reason to change the formula I'm currently using.
 
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I have an unusual need. My bicycle has drum brakes, which are oiled to prevent the steel shoes from galling against the steel drum. They work okay, but they're not strong enough, and I'm not in a position to have the wheels rebuilt so I can use a different kind of brakes. I'm currently using the thinnest sewing machine oil I can get, just a few drops per brake, but it's still slippery enough that I can't quite skid the rear wheel even if I squeeze the brake lever until it touches the handlebar. I need some kind of lubricant that can re-flow around moving parts the way oil can, and can prevent galling between scrubbing metal parts, but also has a high coefficient of friction unlike normal oil. I had previously tried ATF on the basis that ATF is designed to get sticky when squeezed into a microscopic film, but it didn't actually make any noticeable improvement compared to the thin sewing machine oil I'm using now. (maybe the ATF I used wasn't very good, I dunno.)

Suggestions? Please don't tell me to replace the brakes instead, that's not a viable option and the answer will be no.
On every other bike brake system I have used, when properly set up, should pretty much break the cable, hose, or lever, or cable housing, before you can pull the lever to the bar, so I think you've got more mechanical force to add to the system. I find you can squeeze harder with the lever out away maybe 1.5" from the grip too.
Also you can get adjustable leverage levers for even more mechanical force, I've got Avid Speed Dial 5's on my old mountain bike and they work great, 1 finger V-braking, adjusted to roughly balance the front and rear.
 

fyrstormer

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On every other bike brake system I have used, when properly set up, should pretty much break the cable, hose, or lever, or cable housing, before you can pull the lever to the bar, so I think you've got more mechanical force to add to the system. I find you can squeeze harder with the lever out away maybe 1.5" from the grip too.
Also you can get adjustable leverage levers for even more mechanical force, I've got Avid Speed Dial 5's on my old mountain bike and they work great, 1 finger V-braking, adjusted to roughly balance the front and rear.
I have Avid Speed Dial Ti brake levers with the leverage ratio set as high as possible (most lever travel per unit of cable travel), because roller brakes require high-leverage brake levers. The Speed Dial levers are modified slightly, with the travel-stop screws lengthened and relocated, so the resting position of the levers can be set almost-parallel to the handlebar without the travel-stop screws interfering with the cable-puller-thingy. (I don't know the correct name for that part.) This minimizes the amount of dead travel in the levers without needing to set the bite-point uncomfortably far away from the bar, which would make it painful to squeeze the brake levers hard. I have the bite-point set parallel with the bar, which is also how the hydraulic disc brakes on my other bike are set-up.

While this does technically limit the amount of cable-pull that the levers can achieve before they bottom-out against the handlebar, it didn't actually make a difference in testing. I previously tried maximizing the amount of cable-pull, and even when I squeezed the brake levers as hard as I possibly could, hand pain be [danged] for testing purposes, I still couldn't skid the rear wheel. There is a surprising amount of flex in the components of the roller-brake system, though I couldn't tell you precisely where the flex is occurring. All of the brake parts are steel, but even steel can flex, and I'm guessing the brake drums (being open on one side) were flexing under load. There is a ton of leverage built into the lever-and-cam mechanism that actuates the brake shoes (at least 10:1, but I don't know the exact ratio). Plus the cable itself can stretch, even when using reinforced cables and compressionless housings designed for use with mechanical disc brakes.

No, the problem wasn't lack of cable-pull, but the lubricant preventing the brake shoes from galling against the drum was also preventing a full lockup of the brake. So I returned the brake levers to their previous configuration (the same as I'm currently using), since the extra cable-pull didn't actually improve anything, and I started searching for a lubricant that would do its job without interfering with braking action as much. The current goop I'm using, a paste of light machine oil and diamond powder, increased the braking force significantly, to the point that the cooling fins attached to the brake drums actually started getting hot like they were supposed to. And yet, the brake shoes and brake drums are still mirror-smooth, despite the more aggressive abrasive.
 
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