RONSIM

RONSIM

Well Known Member
The RV-8A I am flying has brakes that get extremely hot, even with short taxi and trying very hard to stay off the brakes. Wheel bearings are staying cool, and I have shimmed to ensure no dragging. In the past, I have blown two pistons because the o-rings (probably) get hot and lose their sealing ability.

Any thoughts?

Thanks
 
Check to make sure your brake pedals are totally free to pivot. The return springs in the master cylinders are quite weak and the slightest resitance in the pedal pivot will cause the cylinders to not fully return to the extended position. The fluid return port in the cylinder is at the very end of the travel and it only takes about 1/8" of travel short of full extension to lock the fluid in the lines, causing the brakes to drag or lock.

Martin Sutter
building and flying RV's since 1988
 
Sounds like the brakes are dragging a little. Several builders, including myself have found the master cylinders do not fully extend (release) when brakes are released, allowing the brakes to drag. There is another thread on this forum with extensive dialog concerning this problem. Hope this helps.
 
Look at the thickness of the pads on both wheels maybe that will give you some clues as to which one is sticking. Try different taxing techniques, and foot positions on the peddles. I have to use the bottoms or the sides. The slightest pressure on the peddles will apply the brakes. Also try taxing after you manually pull on the top of the peddles to see if that helps, if it does then like the other post stated you may need a better return spring.
 
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Thanks for the input

Guys -- thanks much ---- that is my suspicion (master cylinders) -- the pedals have no travel whatsovever before actuating the brakes --- I may try some bungy cords to ensure the pedals stay back -- just to test the theory.

Thanks again!
 
RONSIM said:
Guys -- thanks much ---- that is my suspicion (master cylinders) -- the pedals have no travel whatsovever before actuating the brakes --- I may try some bungy cords to ensure the pedals stay back -- just to test the theory.

Thanks again!
Click to expand...

I know what you mean. Try using the edges of the peddles when taxiing and landing. Don't even touch the brakes until you have no control using the rudder. I think these peddles lend themselves to overuse. We need heel brakes! (I'm kidding :D)

Also, if you can move the pane around on the ground easy without hearing alot of vibration & brake noise it just might be operator error. ;)

Don't ask me how I know that. :cool:
 
I would believe that if you jacked the plane (or one wheel at a time) up, you should be able to answer the technical/operator question. I think if they are getting really hot, it would be very difficult to turn a wheel by hand.
 
Excellent Thread referral -- problem common

Thanks for the thread info --- sounds like a fairly common problem --- everyone has been very helpful and put me on track to adddress the problem.
 
Van's gave me 2 new, stiffer, return springs when I complained that the stock ones were too soft. But even with the stiffer springs, I still had to add some AN6 washers as shims under the springs to ensure the master cylinders extended all the way.

As Martin Sutter already said, it's critical that the master cylinder rods extend all the way at rest to open the compensating ports.

Heinrich Gerhardt
 
I just fitted my wheel pants and noticed during this that it is very easy to let the wheel pant push in on the caliper if it is not located exactly right. That could heat up the brakes easily too.
 
Master cylinders or me?

At 225 hours, I replaced my Matco master cylinders with the Grove units http://www.groveaircraft.com/673.html. These are direct replacements for the Matco's. The only difference in installation is the Grove's won't accept as many washers at the top end due to a heftier (wider) clevis. More expensive than adding a simple spring but they work. Your choice.

I immediately noticed a difference in the way the airplane felt during takeoff and landing. The old cylinders tended not to release the pedal and I could feel the occasional pull while rolling and a touchiness in the brakes where they took little pressure to be applied. Much better now with the change.

So for me I finally answered the question, was it the master cylinders or the operator? It was the cylinders.

Chris
 
Update on the "Bungy-cord" test

Using the information provided from everyone (very helpful), I attached bungy-cords (aircraft quality) to the top of the pedals and put enough tension on them to ensure the pedals stayed up. (I allowed plenty of movement for rudder control) --- after flying and the normal fairly long taxi, I can state that the problem has gone away --- just normal "warm", not hot brakes on return to the hangar.

I will go the spring route as shown in one of the previous threads.

By the way, currently building a -10 with first flight "sometime" in 2008.

Thanks again for all the help.

Ron
 
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