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Dual puck brakes?

garrys

Active Member
I have 800 hours on my RV7A. The brakes have always required extraordinary pressure to get any braking at all. I can’t even do a 1600 rpm run up without creeping. After trouble shooting everything I can think of I had my local A&P go through them, with nothing appearing amiss. He suggested installing a “dual puck” system. Has anyone ever done this or heard of such a thing? Where would I start to look? I really need the help of you kind folks.

No, there is no air in the lines, the brake linings are new, the wheel cylinders O rings have been replaced, the master cylinders have been inspected and appear to function normally. This isn’t brain surgery, so why the problems?
 
Have you had another RV pilot try it in your plane for comparison, or vice-versa? And, are you sure that your feet aren't mainly pushing on the rudder cross bars, instead of tilting the brake pedals forward? Are the pedal geometry/hole locations per plans? Has this persisted through multiple brake pads? There aren't many things that could explain this observation...
 
Dual brake pucks

Yes, I’ve had my A&P high speed taxi the plane and he gets the same reaction.
 
Brakes

Yes, I’ve had my A&P high speed taxi the plane and he gets the same reaction.

Something isn’t right. The stock brakes have plenty of braking power. When I took transition training with Mike Segar in the -7, the brakes seemed hard to press with very little braking. Then I realized that I wasn’t getting my toes up to the tops of the pedals. Once I adjusted my feet position, I found the brakes to be much more effective.

Skylor
 
Last edited:
Were the pads properly "bedded" in?

Matco instructions:

Question:
Why do my brakes feel spongy or weak?
Answer:
Check to ensure that there is no air in the system. Air can be trapped in
any high spot in the line and often cannot be "pumped" out. Ensure no high
spots during bleeding.
Check to ensure that your linings have been adequately broken in using a
standard break in procedure. Your lining should produce a shiny transfer
layer if properly conditioned. The following procedure should be adequate to
condition the linings: 1) Apply brake pressure for high throttle static
run-up. Note RPM at creep if any. 2) Perform 2-3 high-speed taxi runs (firm
braking from 30-40 mph to 5 mph) to generate 300-400 degrees at brake pads.
Do not bring aircraft to a complete stop during the taxi runs and also allow
the aircraft to roll until back to the tie down area. Release brake pressure
at tie down area as soon as practicable and park with brake pressure off. 3)
Allow brakes to cool 10-15 minutes. 4) Repeat step 1. There should be a
noticeable increase in holding torque. Repeat steps 1-3 if necessary.
Properly conditioned pads and discs will have a uniform, shiny appearance on
the surface.
 
Master Cylinder Diameter?

I replaced the Cleveland master cylinders in our RV-6 with Matco cylinders because the whole cylinders cost less than the parts to repair the Clevelands. The Matcos were a little bigger diameter so we lost a bit of hydraulic advantage. The effort at the park pedal was much higher with the bigger Matcos. I'll bite the bullet, buy parts and go ahead and fix the Clevelands one of these days. Anyway, suggest you see if you can find smaller diameter master cylinders. BTW, air in the system will make the brakes soft, but should not require any extraordinary pressure on the pedals to get the braking action you want. On another note, if you overdo the extra hydraulic advantage, you run the risk of having enough brake to easily put the airplane on its nose, which could ruin your whole day.
 
I change my Matco pads ever annual. I follow their break in procedure and they hold fine past 1700 rpm. Without the break in procedure I start to roll between 1500 & 1600 rpm. Some say it’s not needed. For my plane, it’s needed.
 
If you are one to believe in “bedding” the brakes, and there is a lot of opinions about it. Make sure you do it with the wheel pants off, and let them cool completely between runs. A lot of planes have caught fire doing that
 
He suggested installing a “dual puck” system. Has anyone ever done this or heard of such a thing? Where would I start to look? I really need the help of you kind folks

The original Matco brakes I received with my kit are “dual puck”. I clearly remember the installation instructions referenced only Cleveland brakes and how one puck had to be removed. After contacting Vans they confirmed that no pucks had to be removed with the Matco calipers. Great brakes, easily hold at 2300 RPM for short field takeoffs.
 
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