Caliper Seal Question - Problems, Questions and Technical

Does anyone know a source for small (3/8"-3/4" OD range) piston cup seals? Metric sizes in that range are fine. Mcmaster only carries them down to 3.5" OD, way too big, and google hasn't turned up anything promising.

The pistons are low speed, relatively low pressure (<100 PSI), and running with water, low-viscosity mineral oil, vodka, or water and antifreeze. (Yeah, unusual hydraulic fluid, eh?) The piston and bore are both aluminum. The cylinder bore is a milled or reamed <32rms finish. Seal life of 1-2 years is acceptable.

I'm open to making my own seals, if anyone knows how, and also to alternate seal types.

If you're wondering what I'm working on, it's a hydraulic brake for a bike.

Thanks a bunch for any help. This really has me stuck. Maybe I am not thinking of the correct item, but:

I would think any antique auto shop should have access down to 3/4". My father used to have a box full of odds and ends of cups for wheel cylinders, and I am pretty sure they were down in that range.

Here is a web site I just found quickly - not a recommendation.

Welcome to Precixinc.com

bob

PS - Vodka? Is this a russian bike? Use the the term "U-Cup Lip Seal" to find what you want.

Here's one source that covers all the sizes you are considering.

http://www.lutzsales.com/Lutz_U-Cup_Sizes.pdf

If you're not joking about your fluid choices be very careful selecting a compatible seal material. Also consider corrosion of your aluminum components with some of your choices, it's not a trivial matter.

If plain jane DOT-3 brake fluid is a possibility consider using it. It is easy to find compatible seals for it and it has good seal lubricity. It is also compatible with aluminum components. Thanks so much for the references, guys. That was exactly what I needed.

Bob, I appreciate the suggestion. I had thought of grooves with o-rings, but relatively low sliding friction is important, so I figured the preload necessary for o-ring seals would be a problem. I plan on doing some mockups to test this, however.

I was not joking about the hydraulic fluid choices. Hydraulic rim brakes are used in two niche sports, namely trials bicycling and offroad unicycling. Since heat generation during braking is not a problem in these sports, many people bleed their own brakes, and use whatever they have on hand for it, including the substances I listed before. There is a tradition of bleeding brakes with water to reduce the resistance of the brake lever, however water freezes too easily, hence the additives and similar substances I listed.

I presume its the antifreeze that is a problem with corrosion of the aluminum and seals, no? I have run a hydraulic brake bled with tap water for 2 years without leaks.

On a related note, if anyone knows of a notably low cost, low viscosity, high lubricity oil for this application, I'm all ears. I am currently testing a brake with extra light vegetable oil. So far, so good.