Brake caliper check

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woxof

Pre-takeoff checklist
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woxof
Just read the quote below on another forum. Never heard of that before. I did realize that some play was normal. But is it really mandatory?


"Checking that a Cleveland brake caliper is 'loose' should be part of a pre-flight inspection. If it doesn't wiggle, it can lock up on you and run you off the runway."
 
Indeed:

 
It is very unpleasant when the brake drags at an inopportune time. An A&P can correct me but my understanding is that the pins should not be oiled (which will just gather dirt). I have heard of antiseize being used...
 
GeorgeC said:
It is very unpleasant when the brake drags at an inopportune time. An A&P can correct me but my understanding is that the pins should not be oiled (which will just gather dirt). I have heard of antiseize being used...
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Those pins should be clean and dry. Oil or grease or antiseize will sludge them up and the problems get bigger. I've had to remove a lot of those to get them cleaned up.

About the only thing that might help would be dry silicone lube spray, but it's so thin that the elements will take it off quickly. Dry graphite won't even stick, out in the wind and rain and all.
Generally, dragging brakes have other causes. The caliper piston might be seizing. The master cylinder return spring might be weak and failing to open the relief valve, trapping pressure in the system.

One more that often crops up in annuals: worn brake discs. Those discs, depending on part number, have a minimum thickness specification, and I've often found them well below that. A thin disc can't absorb as much heat and the brakes will fade on a hard stop.
 
How do you check the brake pads on an airplane with wheel pants?
 
GeorgeC said:
I have heard of antiseize being used...
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As mentioned above best to keep pins dry and clean. Have also polished them in cases of surface damage. The only trick I recall from years back that "worked" was to wax the pins with a hard wax. But it was only used to get to the next brake pad replacement.
 
Brake caliper pistons apply hydraulic pressure when you push the pedals but there’s no retraction mechanism when you let off the pedals. The tolerance between brake pads and rotors is very small. As brake pads wear we add fluid to the system so that tolerance remains constant. Go jiggle on your calipers and you’ll be lucky to notice any movement.
 
You'll want to make sure the bolts are torqued to spec and not overtorqued. Overtorqueing can cause warpage and release problems.
 
Chip Sylverne said:
You'll want to make sure the bolts are torqued to spec and not overtorqued. Overtorqueing can cause warpage and release problems.
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I had an overtorqued bolt break during taxi. Removing the broken bits revealed considerable stretching in the threads from mechanics just cranking on the wrench instead of looking up the proper torque.
 
This is what happens when you taxi a C182 with dragging brakes. In this case it was caused by the loose nut connecting the yoke to the left front seat.

20170604_150247.jpg 20170604_150353.jpg 20170604_150430.jpg
 
Bell206 said:
As mentioned above best to keep pins dry and clean. Have also polished them in cases of surface damage. The only trick I recall from years back that "worked" was to wax the pins with a hard wax. But it was only used to get to the next brake pad replacement.
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The hard wax (paraffin) might melt off once the brakes got hot. But that wax is handy in so many other areas. I used it on door latches to lubricate them without attracting dust. Rub it in the slot in the door windowframe where the window hold-open arm runs. It can be used on Cessna seat rails as per suggestion in the maintenance manual, and the seats slide so much better and the aluminum rail is protected from galling against the aluminum roller housing if the wax is there. Got to carve the wax block into a shape that will get the wax under the edges of the rail's top flange. (Any other lubrication such as oiling the rollers is forbidden by the seat rail AD, because dirt is attracted and the roller seizes up. Disgusting how often one finds that.)
 
Dan Thomas said:
About the only thing that might help would be dry silicone lube spray, but it's so thin that the elements will take it off quickly. Dry graphite won't even stick, out in the wind and rain and all.
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Yup. The Cleveland mx manual specifies
  • Silicone Spray
  • Dri-Slide® Multi-Purpose Lubricant
  • LPS Force 842® Dry Moly Lubricant
for dry environments and Lubriplate X-357 Extreme Pressure Moly Lubricant for wet environments.
 
Thanks for the responses. I just want to confirm....are they talking about the small amount of wiggling/movement that can be done when one puts their hand on the housing/unit and gives it a shake?
 
woxof said:
Thanks for the responses. I just want to confirm....are they talking about the small amount of wiggling/movement that can be done when one puts their hand on the housing/unit and gives it a shake?
Click to expand...
That's it.
 
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