Matco Brake Cylinder Seals

[mcgaughy]

I am a very slow builder....have had to move my project a couple of times....lots of valid reasons....

My brake cylinders for my RV7a were received maybe 12 years ago. I'm wondering if I should rebuild (replace O-rings) in the master cylinders before mounting the rudder pedals in the airplane, because maybe the O-rings have aged too much.

I plan to call Matco tomorrow to ask their advice, but wondered if anyone on this forum had experience that could help me decide and offer any advice about the actual disassembly and reassembly. Looks pretty simple....just remove a snap ring and everything should come apart.

Thanks

Ellis
2017 Dues Paid

[JonJay]

Not a bad idea. They are easy to re-assemble.
You might ask them about the internal springs. It has been noted here that the springs might have been changed over the years to a stiffer spring. Verify that with them and let us know. I rebuilt mine last year but didn't notice if the springs where different.

[Robert Anglin]

We have noticed that the springs in the new kits from Van's are a little longer the older ones. We used them to put on the outside above the cylinder to help the return travel of the plunger. If the plunger does not come all the way back to the top the poppet valve will not open and there will be just enough back pressure to make the brake drag a little. The kits or cheap for van's. Last I looked 12-15 dollars. Yours, R.E.A. III #80888

[airtractor8]

Changing the seals would be a very good idea. It is easy to do outside of the fuselage and they are cheap.
My own RV6 build took ten years and I had all sorts of trouble trying to bleed the brakes in my "new" brake system. After much despair and wasted fluid I pulled it all apart to find the seals completely flat No chance of working properly like that...but they were only ten years old...

[snopercod]

I took decades to complete my kit, too. Before flying, I replaced all rubber parts on the entire aircraft which were more than 12 years old - hoses, O-rings, tires, tubes, crankshaft seal, intake tubes, oil return tubes, everything. It's my belief that O-rings may last a little longer - maybe 20 years - but I replaced them anyway. In my case, the Matco brake system was an older design and the master cylinders were "sticking" during taxi testing, causing my brakes to drag. So I replaced the master cylinders and brake assemblies with the latest version. I even replaced the nylon brake lines, too. Brakes are so critical that I just didn't want to worry about them failing and sending me off into the weeds. When you fly your plane for the first time, you'll have plenty to worry about without wondering if that 50c O-ring will hold. Just do it!