REFLECTOR: Toe Brakes, Back Bleeding

[Ron Brown]

Good morning Alex,

I am talking about back bleeding - injecting pressurized fluid at the bleeder port which is the low point - and pushing fluid and air bubbles up to the master.  There are two chambers in the caliper which are connected together by a drilled port.  If the caliper is turned 45 degrees like when installed on the gear leg - it is possible for air to get trapped in the upper part of the bottom piston/cylinder which will cause a soft pedal.

If you are bleeding using the master cylinder and pumping up the system using the rudder pedal, then I agree with you. You would want to point the bleeder valve up so the air exits.

Ron


  ----- Original Message ----- 
  From: Alex Balic 
  To: 'Velocity Aircraft Owners and Builders list' 
  Sent: Sunday, June 10, 2007 10:56 AM
  Subject: Re: REFLECTOR: Toe Brakes, Back Bleeding


  Hey Ron- I am not sure how you will be able to remove all of the air from your bleeder is not at the high point- if you have been able to do that, then you are very lucky! - if it turns out that you still have some air in there, you might want to remove the caliper from the wheel, turn it so that the bleeder is up, bleed them that way, and then without of course disconnecting them, put them back on the axle...

   

  Alex

   


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  From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On Behalf Of Ron Brown
  Sent: Sunday, June 10, 2007 8:03 AM
  To: Velocity Aircraft Owners and Builders list
  Subject: Re: REFLECTOR: Toe Brakes, Back Bleeding

   

  I had one brake that was soft and had to be pumped.  I thought it was a bad master cylinder and got a new one - same problem.  

   

  Some one had mentioned that air can get trapped in the calipers if they were not turned such that the bleed port was down and the fluid connection at the top.  In other words, take the caliper loose from the gear leg and orient it vertically.  I back bled my brakes from the bottom to the top.  Problem fixed.

   

  I bought the oil can back bleeder from MATCO.  I have seen similar oilers in the hardware stores.  

    ----- Original Message ----- 

    From: Hiroo Umeno 

    To: Velocity Aircraft Owners and Builders list 

    Sent: Sunday, June 10, 2007 12:21 AM

    Subject: REFLECTOR: Toe Brakes, again...

     

    The second installment of the ongoing brakes saga. 

     

    My setup is a factory toe-brake kit with Matco brakes on FG SUV (std fuselage, std wing).  My brake lines are a combination of the hard aluminum line from forward bulkhead to gear bulkhead and the factory provided nylaflow line, the rest of the way.

     

    It was a rainy day today and I decided to bleed the brake system.  I drained the system of fluid, then re-filled it.  I generally do this "bottom up" where I start filling the fluid from the lowest point in the system (bleed valve at the gear) and fill the fluid until the reservoir is full.  My thinking is that going bottom up will ensure that there are no trapped bubbles in the system.

     

    The brake is way too "soft" for my liking, still.  There is quite a bit of toe motion when pushing on the brakes.  It is a lot more than what I am used to on Cessnas and Pipers.  On those, I get the "push back" almost as soon as I get my toe on the brakes and there is very little room to Squeeze.  On my plane, it feels like I am displacing a lot of fluid through the master cylinder.  Shouldn't there be very little movement on the pedals?  The way I understand the system work is that there should be very little fluid movement and the brake should work by pressurizing the system and not displacing.

     

    Curiously, I found that the passenger side left brake feels "taught".  All the rest felt rather mushy.

     

    Aside from bleeding again to check for air bubbles, what else should I check?  There are no leaks in the system along the way, either.

     

    Hiroo

     


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