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  #1  
Old 03-20-2018, 11:04 AM
337_Driver 337_Driver is offline
 
Join Date: Feb 2018
Location: Youngsville, NC
Posts: 23
Default Brake dragging?

So I just recently purchased a new to me RV4. I had to take the wheel pants off to put some air in the tires, and I filled them up to 38psi. I noticed on my next flight when I would apply the brakes with half force or more I would get what felt like a dragging wheel or shudder. I could feel the gear leg flexing in a sense, you hit the brakes and after a couple of seconds its like it grabs or something. Has anyone experienced this? I have the tall gear on my aircraft. Thanks in advance.
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  #2  
Old 03-20-2018, 11:34 AM
fixnflyguy fixnflyguy is offline
 
Join Date: Jan 2006
Location: Winston-Salem, N.C.
Posts: 926
Default Maybe..

They can stick if the puck and or sliders are gunked up. I have had it on mine, and simply cleaned them up. The standard equipment brakes are very simple and pretty bullet proof. It is most prone when new pads are installed, and the puck is pushed back in without being cleaned well.
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  #3  
Old 03-20-2018, 11:35 AM
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JonJay JonJay is offline
 
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In your hangar, or a level place on the ramp, push the airplane forward. Get in, apply brakes, then get out and try pushing the airplane again. If you notice dragging, there are good posts here on how to fix it. It is typically caused by poor pedal hardware alignment that does not allow the master cylinder to retract back to the open position.
You can also just apply the brakes and reach down and see if the cylinder sprang back by lifting on the top of the pedal.
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  #4  
Old 03-20-2018, 12:06 PM
337_Driver 337_Driver is offline
 
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Copy all everyone. I did want to add that this was not the case until after I added air to the tires. I believe this to just be a weird coincidence.
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  #5  
Old 03-20-2018, 12:21 PM
greghughespdx greghughespdx is offline
 
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Location: Aurora, OR
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Quote:
Originally Posted by 337_Driver View Post
Copy all everyone. I did want to add that this was not the case until after I added air to the tires. I believe this to just be a weird coincidence.
Just in case, have you looked at the tire for and rubbing wear after this happens? Depending on how much air you added and shape changes, that's at least a possibility to also consider.
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  #6  
Old 03-20-2018, 12:28 PM
337_Driver 337_Driver is offline
 
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Location: Youngsville, NC
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Quote:
Originally Posted by greghughespdx View Post
Just in case, have you looked at the tire for and rubbing wear after this happens? Depending on how much air you added and shape changes, that's at least a possibility to also consider.

Yep, I actually clearanced the wheel pants a little more b/c prior to adding some air they were very lightly dragging some.
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  #7  
Old 03-20-2018, 07:24 PM
Michael Henning Michael Henning is offline
 
Join Date: Jun 2011
Location: Nashua, NH
Posts: 483
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I run 32 psi in my tires. You mentioned it felt like you had some shimmy going... the -4 is prone to that if psi isnít right.
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  #8  
Old 03-20-2018, 09:30 PM
mattsrv7 mattsrv7 is offline
 
Join Date: Jul 2008
Location: Seattle, WA
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Higher pressures can cause gear leg shimmy.

The builder I bought my -4 from said run 25 psi.

I tried 35 psi once, the difference was remarkable. I quickly went back to 25.

Some experimentation may be required to find what is right for your airplane.
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  #9  
Old 03-20-2018, 09:38 PM
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Ironflight Ironflight is offline
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Location: Dayton, NV
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Quote:
Originally Posted by 337_Driver View Post
Copy all everyone. I did want to add that this was not the case until after I added air to the tires. I believe this to just be a weird coincidence.
Very likely this is not a coincidence - what you describe sounds very much like gear shimmy, and that (as mentioned by someone above) is very dependent on tire pressure. Find out what the previous owner ran for pressure and try that again. These gear are just prone to shimmy, and each has a different set of conditions where it happens.
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  #10  
Old 03-23-2018, 06:39 AM
Vac Vac is offline
 
Join Date: Jul 2009
Location: Niceville, Florida
Posts: 346
Default Try letting some air out...

I run 24-28 PSI in my four to mitigate shimmy. The lower pressure increases the scrubbing action of the tires on pavement and does a nice job of damping shimmy. It does, however, make the airplane a bit harder to push and pull into, out of and around the hangar (and reduces gas milage while taxiing ). Damping shimmy also helps reduce some of the stress on the engine mount/gear leg interface (which may suffer cracking at the welds and should be inspected regularly).


Cheers,

Vac
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