It depends when it was built as to whether it originally had car fluid or hydraulic oil.
The Cleveland brake systems come fitted with bn seals (nitrile) and yes as Rob says the seal will break down with the auto product. The G109 for instance uses auto so you have to change the seals over when you replace cylinders. The advantage of mineral oil/hydraulic oil is that it doesn’t readily absorb moisture in contrast to auto fluid. That advantage results in less risk of corrosion in the internals of the cylinders. Rob has recently had to overhaul some calipers where this was an issue. If the bore gets too pitted it is all over and time to buy a new one. The master cylinder is not a motorcycle unit as many other manufacturers have adopted. It is a Cleveland with park brake valve and external reservoir. Also more expensive than the other type as used in Pawnee’s . In the HK36 the slaves are Cleveland but the masters which are on both pedals for steering brakes are Matco mfg. That surprises me as Matco supplies the experimental market and I don’t think they have any certified equipment. How diamond does that I don’t understand but there is obviously a work round under EASA. All the Matco stuff comes with BN seals fitted which is the industry norm as in GA mineral based hydraulic oil is the norm. Cars often suffer long hill decent profiles that cause significant heat problems and the auto fluid id made to take that heat without boiling. Aircraft generally don’t get exposed to that problem. Schemp Hirth and others tend to use motorcycle master cylinders so seem to mainly use auto fluid I guess to avoid changing seals. I am sticking with cheap mineral hydraulic oil. I always seem to have an abundance of it around the place and have dealt with brakes running on car fluid in both cars and gliders and not forgetting the old rarely maintained glider trailer and experienced significant corrosion issues many times. When I changed the axle in my trailer recently I went for mechanical disk brakes for that very reason. Ill stick with mineral thanks. Fly Safe. Nige. From: dog@lists.riverland.net.au <dog@lists.riverland.net.au> On Behalf Of Rob Thompson Sent: Sunday, June 24, 2018 7:29 PM To: dog@lists.riverland.net.au Subject: Re: [DOG mailing list] NO AUTOMOTIVE BRAKE FLUID IN H36 Hi Michael, So you have been running water soluble auto fluid in Cleveland brakes for 17 years? Interesting. I didn't think the rubber bits would go OK with a water/glycol based fluid. Make sure you label the reservoir very clearly what type you are using. If someone adds the wrong type you will get a horrible mess! regards Rob Rob Thompson 0429 493 828 (Please note that my new email address is amessageto...@gmail.com <mailto:amessageto...@gmail.com> ) On Sun, Jun 24, 2018 at 9:26 AM, Michael Stockhill <sto...@gmail.com <mailto:sto...@gmail.com> > wrote: I believe the service manual specifies automotive type fluid, likely for the motorcycle type master cylinder. No problem with Cleveland O rings in slaves for last 17 years. Best Michael Stockhill On Jun 23, 2018 3:01 PM, "Rob Thompson" <amessageto...@gmail.com <mailto:amessageto...@gmail.com> > wrote: Just a reminder to everyone and Martin from K1W1 land. The H36 uses hydraulic brake fluid. Auto fluid is water based and will wreck the seals and system. regards Rob Rob Thompson 0429 493 828 (Please note that my new email address is amessageto...@gmail.com <mailto:amessageto...@gmail.com> )
