RV10Rob

RV10Rob

Well Known Member
Hi, all... six months ago, back in this thread, I had some questions about brake drag. After 80 hours and about 140 landings on the plane now, I'm still seeing this problem. Looking carefully, it appears the plate is sliding freely on the pins, but the piston is holding too much pressure on the pads against the rotor, after the brakes are released. Seems weird, since I haven't heard of this problem on new airplanes, all my components are new, and I'm seeing this on both sides.

Here's a video of me spinning one of the wheels, with no pressure on the brake pedals and pulling up on them to ensure they're not "sticking" down (which I know is a common problem). Drag seems excessive:
http://www.youtube.com/watch?v=-JFTeGMazqs

If I pull the brake pads apart, off the rotor, I have very little drag:
http://www.youtube.com/watch?v=8SUUfM0KsIg

What's an acceptable amount of brake drag? I'm guessing much less than this. Note I haven't seen any evidence of overheating, and the wear on the tires doesn't seem that out of line. Any similar experiences or advice appreciated. Thanks...

-Rob
 
It is hard to tell if you have a tad too much bearing drag or if you indeed have a piston hanging up in the caliper. Try taking the pad off and spin it. If it is notiably different then you might want to take the caliper apart and take a look. Might have a pinched oring or debris between the piston and the piston wall. It is going to drag a little. It looks fairly normal. How are the pads looking? Wear even?
 
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Geico266 said:
It is hard to tell if you have a tad too much bearing drag or if you indeed have a piston hanging up in the caliper. Try taking the pad off and spin it. If it is notiably different then you might want to take the caliper apart and take a look. Might have a pinched oring or debris between the piston and the piston wall. It is going to drag a little. It looks fairly normal. How are the pads looking? Wear even?
Click to expand...

Thanks, Larry... in the second video I posted above, I pulled the pads apart so that they're not contacting the rotor, and you can see that there's hardly any drag, so it's not the bearings. I think it's more than "a little" drag in the other video, with the pads in contact. Pads have hardly worn at all (I operate off a long runway and usually avoid braking as much as possible). Next step will be to take the brakes apart, but want to make sure I really have a problem and that there's no easier solution before doing that. Seems weird that there would be a problem on both sides, since all the components are new.

-Rob
 
Sorry Rob, I had not looked at the second video.

Is the piston assembly able to flex freely?
 
Rob--check the master cylinders-

to make sure they are not holding residual pressure in the lines. The master cylinder pistons should be fully retracted when not using the brakes. Even the slightlest depression of the piston can keep enough pressure on the Caliper piston to make the pads drag.--
Race car stuff, but works on planes too-
Tom
 
Thanks, guys... when I was doing research on the problem, I came across the threads on the pedals not retracting fully and adding the springs. I pulled back on the pedals to make sure that's not the problem.

-Rob
 
Try taking the piston out of the caliper and checking the piston / cylinder clearance. Take the assembly off the plane and use a little compressed air and it will pop the cylinder right out. Be careful does not take much! Look for debris between the piston and the cylinder wall.

Obviously, you will need to bleed that brake line again.
 
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