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Brake Master Cylinder newbie question

rcsilvmac

Well Known Member
I am not very mechanically inclined, but my RV-6A is insisting I learn. I recently had the right brake lose pressure. Of course I need to bleed the brakes...so I spent the better part of a day figuring that out, then discovered that I had a leaking Cleveland master cylinder on the left pilot pedal. After researching this item, it seems the prudent thing to do is to replace it with a Matco one. Should I replace both on that side? What is the right replacement Matco part to purchase? Any advice before I embark on this next project? How do I keep the brake fluid from draining out all over my interior?

Thanks, and go easy on me!
 

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Since you state you are not that mechanical I would suggest finding someone who has worked on 6’s to help you. What you want to do is awkward and possibly frustrating. Tool selection and tightening will be a challenge.

Find a mentor
 
Master cylinders

These are fairly simple units to service and any shop can do that. If you want to attempt it, just don’t use automotive brake fluid. If you decide to go with Matco units, I’d buy these.
Jason
 
Why not consider simply rebuilding the Cleveland master cylinders? Easy to do. Aircraft Spruce sells a kit that includes all the parts and detailed instructions.

Others would argue that you don't even need the kit, instead all you need is a couple o-rings for each master cylinder.

The kit just makes it easy to get the right size parts easily and conveniently.

With regards to your question about the brake fluid all over your interior: before you start you will need to drain all of the brake fluid out of the system. Easily done by opening the bleed screw at the bottom of each brake caliper (after providing some means to catch the draining fluid). Let it all drain out. Replace with new after the master cylinder rebuild.

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Rebuild the MC's. Good pics Dave. I just did it again (different airplane). You do not need to drain the system but cap off the line to the brakes (unscrewed from the MC). When you are done and pushing fluid in from the calipers it will push the remaining fluid up through the system bubble free.
 
Thanks - going to rebuild

I am going to follow Dave's suggestions and tackle a rebuild. Dave, thanks for the pictures!

This forum is one of the key reasons I own an RV. Thanks for the support!
 
Chris----you might check the cure dates on the hoses----just from the pics they look old and stiff. Even though 5606 doesnt deteriorate the hose liner like fuels do, the hoses do get pretty stiff. While you are laying upside down in the plane---might be good to look things over---including the plastic hoses you have.

Tom
 
Journey continues

I rebuilt the cylinders on the left side and re-assembled everything. Of course I got a few things wrong the first couple times I re-assembled... now I am back to my original issue. The co-pilot right brake goes to the floor. When I try to bleed the brakes the system gets fully pressurized but doesn't fill fluid on the right brake side. The left brakes work great, and after full bleeding the right brake on the pilot side will work for a bit, but eventually starts losing pressure (after about 7 landings). For some reason it seems to me the right co-pilot brake cylinder is "frozen" or blocked? If I push on the co-pilot right brake pedal I can see some fluid moving in the cross over line, so it seems like the plunger is working. I am now going to search for a detailed description of how the brake system works and try to figure out what to try next. At this point I assume I will need to rebuild the cylinder on the co-pilot right brake, but also think there might be some other issue. Thoughts?
 
Google search much better...

after searching the RV-6 forum on this site I couldn't find any description of the brake system. I then went to google, searched "RV-6 brake system) and found this thread:
https://vansairforce.net/community/showthread.php?t=163488

I think my co-pilot right brake cylinder is not releasing, so I can't get fluid into the right brake system when I try to bleed. I will check the travel and locate a spring locally to see if that fixes it. I will post the outcome later. :)
 
Braks

You should rebuild the copilots master cylinder as well. The o rings get old and stif. The lower plunger can’t slide up to allow the fluid to back flow.
Hope this helps.

RD
 
Do you have an RV-6A or an RV-6. Doesn't matter, but your original post says RV-6A in the post text, but the signature says RV-6. Either way, here are the plans for the tri-gear and tailwheel RV6 brake systems.

RV6-brakes.jpg

RV6A-brakes.jpg

Sounds like your left side is bleeding properly, but on the right side the fluid isn't getting past the passenger side right master cylinder and up into the reservoir (bleeding from the bottom up).

Makes sure the tops of the brake pedals are all the way aft (thus no pressure on the master cylinder). What I have done in the past is use bungee cords or string/rope on each pedal pulling the tops of the pedals aft and attaching the bungee cords or rope to anything that will work (like the bottom of the control sticks). Anything to assure there is no pressure on the master cylinders.

Also I like to use a 1/8 NPT hose nipple on the top of the brake reservoir with a clear hose into a catch can. Keep filling from the bottom until the clear hose from the reservoir to the catch can is running with fluid bubble free. You may need to wiggle or tap or vibrate the hoses between the pilot and passengers pedals at this time to get those pesky air bubbles out. Then do the other side.

Once you're all done its a little bit of a mess disconnecting the hose at the reservoir, just be careful. Then adjust the fluid in the reservoir so that it is about 1/2 to 3/4 full. I use a syringe to pull some fluid out.

You'll get it sorted.
 
Parts

I have the Cleveland Brake catalog which will have an illustrated parts break out which is what I used to rebuild mine. I go to the local O-ring supplier in town and buy the parts for about 25% of Spruce. Sorry spruce, call me resourceful.

I will be glad to email you the info.
 
Maybe you could try a brake pedal return spring mod:

https://vansairforce.net/community/showthread.php?t=115580

Go to post #5 for a pic.

I put one of these on my first RV after the internal master cylinder spring didn’t seen to be working as well. It pulls the pedal back to it’s neutral position so master cylinder isn’t partially open. I don’t remember who sold this kit when I bought it, but it was an easy install and it worked.
 
I have the Cleveland Brake catalog which will have an illustrated parts break out which is what I used to rebuild mine. I go to the local O-ring supplier in town and buy the parts for about 25% of Spruce. Sorry spruce, call me resourceful.

I will be glad to email you the info.

Be careful with off mil spec O-Rings. I rebuild master cylinders and had to remove and replace some o-rings that looked the right size but were not and leaked.
 
Thanks, in progress

I appreciate all the pointers. I have ordered the parts to rebuild the passenger cylinders as well as the “spring mod” to increase pressure on all 4 cylinders. Hopefully will get all that done next weekend. Will let everyone know how it goes. I am now becoming knowledgeable on RV-6 brake systems!
 
Cleveland 10-30s

Like some older RVs I have Cleveland 10-30 masters on the pilot side. Since I'm down the rabbit hole of addressing leaks on the Matcos and the cracked rudder pedals, thought to go ahead and O/H the Clevelands.

Now the Clevelands were working fine, not leaking. On disassembly they were clean, no real wear or scratches. O-rings even looked good, though there was some dirty brake fluid inside.

what's really odd...My part #8 springs 082-14500 measure w/calipers to 3.5 in. free length. The Cleveland spec calls for 4.55 in. for mine, and 3.60 on some sibling models 10-30c.

so my springs have been significantly shorter than spec? Kind of scratching my head. Needle in a haystack but wonder if anyone else has seen this.
 

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It is easy for a large bubble to get trapped. I find it helps to lift up the pedals to get the master Cylinders close to horizontal and stick a box or something underneath to hold them there. Then try your bleeding again.
 
I have the Cleveland Brake catalog which will have an illustrated parts break out which is what I used to rebuild mine. I go to the local O-ring supplier in town and buy the parts for about 25% of Spruce. Sorry spruce, call me resourceful.

I will be glad to email you the info.

Are you really going to try to save a few pennies on O rings? I'm with Gary on this one; the cost savings don't add up to enough to justify the end result.

You know how copper wire was invented right? :D

-Marc
 
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