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How do the RV-10 brakes work?

jtrollin

Well Known Member
I just installed new brake pads because I had a brake failure and now my brakes stick REALLY bad, like I can't push the plane myself bad. So what causes the brake piston to retract in to the brake housing? What things can cause a brake to stick. Looking at the whole brake system, I don't see anything that would actually cause that piston to retract at all and it does not slide in and out very easily.

Any ideas or things to look at would be a huge help.

thanks,

John
 
I just installed new brake pads because I had a brake failure and now my brakes stick REALLY bad, like I can't push the plane myself bad. So what causes the brake piston to retract in to the brake housing? What things can cause a brake to stick. Looking at the whole brake system, I don't see anything that would actually cause that piston to retract at all and it does not slide in and out very easily.

Any ideas or things to look at would be a huge help.

thanks,

John

Lots of questions……..

Whose brakes do you have?

I know at least on the RV-10, the rudder pedal frames can be out of square. This causes side loading of the cylinders. This wears the o-rings in the cylinder prematurely. On mine, one pedal was off a 1/8”. A couple washers resolved the issue.

When the o-ring fails, there tends to be some black goop accumulate around the top of the cylinder. You can buy a rebuild kit from ACS for about $13 or so for Matco cylinders. I don’t know the costs on other brands.

You can put return springs on the cylinders to assist them releasing hydraulic pressure. Just make sure that the springs can’t scratch the cylinders.

Have you checked check to ensure that none of the parts have over heated and warped? This will caused brakes to drag as well.
 
I have the cleveland brakes and Matco cylinders that came with the kit. My right pads were worn completely while my left pads were barely half way worn down. I guess I will check the cylinders of the right brake on the pilot side (no one ever uses the copilot brakes) and see if I can detect any issues there.

That being said, does releasing pressure on the cylinder actually pull the pads away from the disc, or does not having pressure on the cylinder just allow the pads to move themselves away from the disc?

Can you explain what you mean by side loading the cylinder, not sure I am following what to look for there?

thanks,
 
John,

If the stock brakes on the -10 (Matco) are anything like the -7 (Matco) and every common auto disc brake system around, the "wobble" of the disc is what pushes the brake puck back towards the cylinder, effectively "retracting" the pads.

Any extreme sticking of the brakes or uneven wear like you mention is caused by some other force acting on the system. rleffler mentioned some specific areas to check.

I would also add that a simple brake system like this can accumulate enough trash on the guide rods and such to prevent smooth brake action. Maybe a disassemble and cleanup would reveal some wear spots (worn plating or scuffing) that would lead you to a solution. You should also lube the guide rods with disc brake lube when reassembling.

As a side note, my -7 has the extra retraction springs on the "Master" cylinders at each pedal and have worked great since day one. YMMV

Cheers
 
I believe the OP was asking about the piston on the brakes themselves, near the wheel, not the actuating piston attached to the pedals.
There are two things to check. First, look at the pedals and actuating cylinders near the pedals. Make sure that they are fully retracted. Some of them can have some binding and not fully retract, leaving fluid pressure in the system. Some builders have put small retraction springs on the pedals, to insure they fully retract.
Next, look at the brakes on the wheel. The way they work is that the brake piston pushes against the inboard pad. This pushes the pad against the disk, and at the same time the entire piston assembly moves inboard, dragging the outboard brake pad with it, against the outboard side of the disk. The assembly is held in place and guided by some cylinder-shaped pieces of steel, over which it must smoothly move. Sometimes this gets "gunky" for lack of a better word. Clean the area where the metal to metal sliding happens, then spray with some dry high temp lube.
 
This is how automotive brakes work, I 've never been in an aircraft brake system but I would think it's the same.

The seal is a square cut O ring and the piston flexes the O ring a small amount. When you let off the brake the O ring returns to shape and pulls the piston back.

https://youtu.be/PE7yFJ8ldVc
 
RV's use a round "O" ring. But it does the same thing. When the pressure is released, the piston only move a few thousands to release the disc. It can still be touching the disc with no pressure applied. If the pedal piston did not move to open the inlet port, the brake will still be applied..... That is how the optional parking brake works.
 
Pedals

Those os use build the RV7A/9A planes have been modifyig the brake pedals to make sure there is no drag causing the pedals to hang up. In my case, I used a stainless steel rod as a pivot so the pedals return easily to their normal position and do not hold one caliber engaged.
 
Don't have the source anymore but I am doing the master cylinder spring and single long pedal shaft mod on my RV-10. All parts from McMaster:
8 x 9440T63 bronze sleeve
1 x 8893K178 rod
8 x 6432K19 set screw shaft collar
8 x 6389K625 nylon sleeve
4 x 9657K432 spring

$72 plus shipping
 
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A couple of other things to look at...

- Make sure the wheel pant support is not contacting the brake assembly.

- Check the brake plate, this is the part that is bolted to the axle. There are two bushings in the brake plate that support the pins on the brake caliper housing. The brake caliper should move freely when inserted into these holes. When I installed my Matco brakes new, there was some binding. One of the bushings had a deformity from manufacturing so I sent it back.

I also installed the return springs. Before that it was really difficult to know if something was dragging.
 
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