On Tuesday, January 6, 2015 7:02:07 PM UTC-8, Larry Suter wrote:
Just got a new Cleveland caliper assembly for one of our club's G-103's. Grob requires the use of DOT-3 fluid because of the master cylinder. The o-ring in the piston is designed for 5056 fluid. I'm told DOT-3 will call that o-ring to swell. So we need to replace the o-ring.

Does anyone know what common o-ring materials are compatable with DOT-3?

Aircraft Spruce, BTW, doesn't sell DOT-3 compatable o-rings.

Thanks,
Larry

EPDM rubber is what you want for DOT 3 compatibility. Look at the following compatibility list, Dot 3 is under "Brake fluid DOT 3, glycol type". Viton is NOT recommended.

I have a whole bag of EPDM O-rings that are the correct size for the Cleveland 300 series brake calipers, as used in most GA Cleveland brakes with 5606 type mineral based fluid (and as used by Stemme GMBH w/DOT fluids) . . . send me a stamped self addressed envelope and I'll send you 4. No charge.

Or, you can order a new MKIV yaw string and I'l throw in the O-rings for free!

Also note that when using DOT-3 fluid it's important to make sure they pucks (pistons) in your caliper are anodized - otherwise they will tend to corrode if there's any water in the system (and sooner or later there will be, as DOT-3 is hygroscopic).

To check the pucks, use an ohmmeter or continuity tester. If the pucks are anodized, putting the probes on the surface will show and open, as the anodize layer is an insulator - bare aluminum conducts of course.

My understanding is that early Cleveland brakes were not anodized while those made in the last decade or so are anodized.

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