REFLECTOR: Toe Brakes, Back Bleeding

Ron Brown romott at roadrunner.com
Sun Jun 10 08:02:47 CDT 2007


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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