N

n38139

Well Known Member
I have an early airplane that have the master cylinders mounted up instead of attaching to the floor. I seem to recall a post about difficulty in getting the air out. I am in the process of refurbing the cockpit and have most of the wiring and instrument panel out. Is there a better way of mounting these or should I just keep what I have? Is it worth the effort? I am changing out the plastic lines for braided regardless.

I also have a parking brake ( I didn't even know about it until I took the panel off) and I was wondering if anybody has come up with a clever solution for a mircoswitch to indicate it is on?

thanks
 
Steve, the early RV-4's had the brake master cylinders mounted on the brake pedals with the springs pointed down. This led to bleeding issues. I converted mine by modifying the brake pedals so that the master cylinders could be mounted with the springs up.

I have my notes and drawings if you are interested. Send me a PM with your email address and I'll send it to you. For me, it was definitely worth the effort to do this mod.
 
older or newer model?

Do I have a newer model or an older model? My cylinders are on the bottom and the shaft come out the top.
Serial # 3409
Finished in 1998.

To bleed from the bottom up it looks like it would work.

Thanks

Tim
 
Pat Hatch said:
I have my notes and drawings if you are interested. Send me a PM with your email address and I'll send it to you.
Click to expand...

Pat....I have the old style with the springs pointed down (I was just staring at them this morning....lol). I'll PM you with my email address....I'd love to see your notes/drawings on flipping or converting them. I've in the process of installing a new motor mount with the longer gear legs, so I have to disconnect the brake lines and drain the brake fluid at the wheels tomorrow anyway...might as well correct the master cylinders while I'm at it.

On a good note, I found that I already have steel braided brake lines, so switching from plastic to braided is one task I get to mark off my 'to-do' list. :D
 
Robert, write-up and drawings sent... hope this solves your problem! Pretty easy fix really. :)
 
Brake bleeding problem

Pat Hatch said:
Robert, write-up and drawings sent... hope this solves your problem! Pretty easy fix really. :)
Click to expand...

Could I have your drawings, I filled the brake lines yesterday and it feels like I have a lot of air in the system.
 
Hans, send me your email address and I'll attach the drawings and photos you want. I sent you a PM also with my email address.
 
Steve and Hans,

I have an older -4 and was having all kinds of trouble bleeding brakes also. Couldn't get the air out. I attempted to flip the master cylinders but there was no clearance between the pedals and the center console for the cylinders. Not being a builder (i.e. equipped/skilled/ambitious enough), I finally figured out the sure-fire way to bleed the system. You could do this as an interim.

Put one of those tanks that fill fluid by being pressurized with compressed air on the fitting in the reservoir. Then take the brake caliper off, compress the piston and turn it upside down (which I consider to be right side up) so the bleed valve is high. Open the valve on the pressurized refill tank to enable the supply flow, then open the bleed valve (catching the overflow) until no more air. Then close all the valves and replace the caliper.

I basically consider both the master cylinders AND the calipers to be upside down on my -4 when it comes to bleeding <flame suit on>. I can see that having the brake line high as it is now might be smart for protecting the lines from damage. The gurus may now slam me if they feel so inclined. :)
 
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Chris, no slam here, I think you can rightfully consider them mounted upside down. Years ago I spoke to an old Piper guy who said the early Pipers mounted the brake masters this way and you actually had to undo them, turn them right-side up, bleed, and then re-install them. What a hassle.

It's actually about a 2-day job to mod them the right way up. But you probably have to have the tools and some building experience to do it. When I first built my RV-4, I had to bleed them the old Piper way, and you can just bleed them normally using an oil can with the fluid and pump from the calipers up to the reservoir. No pressure stuff required. After they're bled, remount them normally. Or you can do the mod. :)
 
Top down bleed

Consider hooking up a pressurized container of hydraulic fluid to your reservoir. Then with an assistant pumping the brakes, you can bleed top down, just like a car vs. the standard aircraft bottom up technique. A quick search will pull up a couple of posts on this topic. Use a clean "catch pan" or return line on the calipers and excess fluid can be recycled. I prefer an open container since its easier to hear and see air being ejected from the system at the caliper. Like automotive brakes, ensure you tighten the bleed valve on the caliper on the pressure stroke (1/4" wrench for standard Cleveland fitting on 30-9 brakes).

You might want to consider Viton o-rings in your calipers before you bleed. There is also good discussion on this on VAF as well regarding advantages.

We've got "upside down" master cylinders in our -4. Only disadvantage is that bleeding isn't a one man operation.

Best of luck,

Vac
 
I just finished building my RV4, it has the upside down MC's. I thought I was in for a frustrating couple of hours to bleed them but it was actually quite easy. I did it this way...YMMV...

1) Unbolt the two AN3 bolts that mount the MC to the rudder peddles
2) secure the MC upright with some safety wire
3) empty the MC reservoir
4) pump fluid up from the brake caliper with an old style oil can filled with brake fluid
5) re-secure the MC and check for a firm peddle.

I had to do the right one twice, but the whole operation took less than an hour, and my brakes are nice and firm.

Cheers,
 
I think all it would take is to swap over the inlet and bleed at each wheel cylinder. Bring the bleeder to the top and you should be able to bleed ib the same way as a road vehicle.
 
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