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Terrible brake life on RV-8A! (with pics)

markserbu

markserbu

Active Member
I went out to the plane to fly to breakfast with friends today and when I opened the hangar, I saw that telltale dark stain under the left main. So I caught a ride in the back of a 182 and took almost twice as long to get there. ;-) Next week I'll be putting the 4TH SET of brake pads on the left wheel in the 2.5 years since I've owned my RV-8A! The last two sets lasted 71 and 88 landings, respectively. The right set has been replaced once, and has lasted somewhere around 200 landings. I found out that the left master cylinder didn't have a strong enough return spring so I made a helper spring which seemed to cure the slight brake drag that I noticed from time to time, but maybe I need to make another one out of heavier wire. I've read the posts here about folks' brake life, and I'm definitely below the low end of the scale. My question for the gang: Has anyone gotten fed up with the terrible brake life and gone with another manufacturer like Beringer? If so did it make a significant difference? I'm perfectly happy to throw a few thousand bucks at the problem if it'll keep me from replacing brake pads every 70 or 80 flights!

As you can see in the pictures, the pads are worn but it sure doesn't seem like they're worn enough to hyperextend the piston and uncover the O-ring. And you can see that the O-ring looks brand new.

IMG_0418.JPG

IMG_0426.JPG

IMG_0427.JPG
 
Some good discussion about why the brakes wear more on the 8 here:

https://vansairforce.net/community/showthread.php?p=1563175

I copied Herman's method and it was fast, easy, and works well.

http://www.rv8.ch/rudder-pedal-mod-to-avoid-dragging-brakes/

I had the problem with brake fluid leaking when the pads were not really worn once. I took everything apart and it all looked fine, so I just cleaned and reassembled, and it didn't leak. No idea if I got a piece of crud in just the right place to cause the o-ring to leak, or what. I'm using DOT 3/4/5.1 glycol-based brake fluid - and yes, I changed all my o-rings and seals to EDPM rubber (thanks Charlie and Mike!)
 
Brake life

Are you certain you have the correct rotor installed and does it meet the thickness specs?
 
Hi Mark,

It could be several factors leading to the leak you've experienced. The piston looks worn. If the aircraft is flying since 2002 that's a lot of taxi time for an A model. In hot climate long taxi wears the components greatly. The brand is solid I think if you replace the major brake assemblies it will give you another 20 year of service.

My airplane is flying since 2011 and I had several similar occasions, lost brakes couple times. I am still on original calipers but thinking of getting new ones. The wear is noticeable.
 
The piston shows corrosion on the exposed side of the O ring.
Check the bore... I expect you will find it corroded also, down to where the O ring rides.

As the pads wear, the O ring reaches the damaged area, it start to leak. You can normally
wear the pads down to the wear indicator notch.

If so, clean up the bore. You should be able to save it.
 
This doesn't explain why the piston extended far enough to leak but your brake pads themselves seem very "course". I have found that some pads have a "more course" material than others and wear faster. Plus they are more prone to have corners break off during installation if you are not careful. Don't remember which ones were like that but have found that the Matco ones had a much "finer" material and seemed to last longer for me. I think the Cleveland ones also have a finer material.

Just an observation unrelated to your problem but something to consider.
Keith
 
Brake issues

Sounds to me from the original post and pics that your caliper is dragging and it’s not only overheating causing the O ring to fail its wearing our brake shoes FAST!
If you have the Matco brake masters that’s your problem. They are notorious to stick and not completely release. Usually it’s always one side or the other to fail only.
Lot of guys add a spring to the shaft to help however in our area most of us just suck it up and replace them with the Grove masters. A much superior Master Cylinder.
 
Not sure if this is an issue with the 8 brake pedals, but on the 6,7, etc...
Was working on a 7, and found that the brake pedal bolts and castle nuts were snugged down! It has to be loose to allow free movement of the brake pedal. hence why a castle nut in that location. Duh! Last worked on... by an A&P. Before getting a bunch of springs make sure the pedal freely moves!
 
Last edited:
Question for OP

How did you “make” your own springs? What material and heat treatment process were used? Just curious.
Terry, CFI (retired metallurgist)
RV 9A N323TP
 
What I’d do- use a red scotchbright pad to reface the cylinder wall & piston. Install a new o-ring & pads (as they are soaked in brake fluid) & go flying.
If the o-ring exhibits even the slightest bit of flat spot from where rubs against the cylinder, it is done. If it feels at all stiff, it was overheated & it’s done.
Best advise to longer lasting brake pads is to let the plane roll out on landing, taxi slower, & just tap the brake to initiate a turn ( not hold & drag a brake thru the turn).
Good luck with your brake wars!
 
Ralph Inkster said:
What I’d do- use a red scotchbright pad to reface the cylinder wall & piston. Install a new o-ring & pads (as they are soaked in brake fluid) & go flying.
If the o-ring exhibits even the slightest bit of flat spot from where rubs against the cylinder, it is done. If it feels at all stiff, it was overheated & it’s done.
Best advise to longer lasting brake pads is to let the plane roll out on landing, taxi slower, & just tap the brake to initiate a turn ( not hold & drag a brake thru the turn).
Good luck with your brake wars!
Click to expand...

I would add, ... taxi RPM is under 1000.

I've got this guy with a Cirrus a few hangars down... starts up, sounds like 1400 rpm. Taxis by blows **** into my hanger if I don't get the door down quick. Can see the plane bobbing as he rides the brakes all the way to run up area.... Geez.
 
Thanks for all the responses...I really appreciate it. I found 2 extra brake pads in the hangar and got the plane going again today. I guess I'm going to buy a new Cleveland caliper assembly and give that a shot. The current one is 23 years old so I guess it's time! Very interesting about the mods folks make to their pedals to avoid engaging the brakes while taxiing. When I flew today I paid particular attention to how I worked the rudder pedals and I actually put the balls of my feet on the very bottom of them. So I don't think it was pilot error that led to the premature wear.
 
terrykohler said:
How did you “make” your own springs? What material and heat treatment process were used? Just curious.
Terry, CFI (retired metallurgist)
RV 9A N323TP
Click to expand...

Ah, a metallurgist! I'm a mechanical engineer/gun designer and own a gun company, so I've had to make lots of springs over the years. Mostly for prototypes. I use plain old music wire, which is basically 1085 steel drawn into wire. I honestly don't know the hardening process but it may just be strain hardening. I know the yield strengths are insane when compared to equivalent bar stock...we're talking 300,000 psi to just over 400,000, based on diameter! The process of making the spring is very simple...just wrap the wire around a steel rod, usually with the rod stuck in a drill or drill press. After winding the spring is stress relieved in a regular (usually toaster) oven at 450 degrees F for 30 minutes. I don't understand what's going on with this 450-degree soak, but I know that if you don't do it the spring will take a set instead of being a good spring. As a metallurgist you may know the secrets of the process.

Spring.JPG
 
Search the forum and you will find a lot of info on how to fix brake drag. Some folks are fine with covering up a poor install with springs. It doesn’t fix the problem, just the symptom. I prefer to fix the problem.
My brakes had drag when I first built the plane. Fixed it within the first few hours and never looked back. Nothing wrong with the Matco cylinders. Thousands out there working just fine.
 
I would measure the disc thickness, perhaps you are using a narrow thickness disc where it needs to be one of the thicker disc's.
 
Check the Disks

Have you measured the thickness of the disks? If the pads are wearing fast, so are the disks.
 
JonJay said:
Search the forum and you will find a lot of info on how to fix brake drag. Some folks are fine with covering up a poor install with springs. It doesn’t fix the problem, just the symptom. I prefer to fix the problem.
My brakes had drag when I first built the plane. Fixed it within the first few hours and never looked back. Nothing wrong with the Matco cylinders. Thousands out there working just fine.
Click to expand...

Yes, I read lots of posts. This wasn't a case of someone tightening the nuts too much 22 years ago, it's a case of the springs losing a bit of strength over the years. The correct fix would have been to replace the springs inside the master cylinders, but this accomplished the same thing in much less time and hassle.
 
MWH265 said:
Have you measured the thickness of the disks? If the pads are wearing fast, so are the disks.
Click to expand...

The discs were new 2 years ago and still look very good. But I ordered a new disc along with a new caliper (left side only for now). Crazy thing is that the disc cost $88 then and are $157 now!
 
markserbu said:
Yes, I read lots of posts. This wasn't a case of someone tightening the nuts too much 22 years ago, it's a case of the springs losing a bit of strength over the years. The correct fix would have been to replace the springs inside the master cylinders, but this accomplished the same thing in much less time and hassle.
Click to expand...

There’s more to it than that, but if that’s your conclusion, that’s fine. Mine are now 18 years and counting with no evidence the springs have weakened. Carry on…..
 
Pads

Go down to your local clutch and brake shop and get some
Good Kevlar material that’s a little thicker than standard.
Cut out some pads. Drill and countersink and Shazam!
Lasts forever, my brakes are a little to powerful and the Kevlar
Material seams to have a little less “grip” which works out
Fine.
 
Ralph Inkster said:
What I’d do- use a red scotchbright pad to reface the cylinder wall & piston. Install a new o-ring & pads (as they are soaked in brake fluid) & go flying.
If the o-ring exhibits even the slightest bit of flat spot from where rubs against the cylinder, it is done. If it feels at all stiff, it was overheated & it’s done.
Best advise to longer lasting brake pads is to let the plane roll out on landing, taxi slower, & just tap the brake to initiate a turn ( not hold & drag a brake thru the turn).
Good luck with your brake wars!
Click to expand...
Thank you, Ralph Inkster! My RV-9A right brake caliper is leaking. I will use red Scotchbrite on the bores and pistons of both and replace the O-rings, once I get the calipers out.
 
You might want to compare the piston installation between the left and right calipers. I once installed a piston backwards and had both short brake pad life and leaking calipers. It happens!
 
Tankerpilot75 said:
You might want to compare the piston installation between the left and right calipers. I once installed a piston backwards and had both short brake pad life and leaking calipers. It happens!
Click to expand...
I know this is an old post. BUT the pictures of the 0-ring that the op started this with must be the wrong one.
I run my tongue around the outer face to make sure it is burr free.
If you look at the ops pictures you will see a casting line on the 0-ring. That 0-ring isn't going to seal very well.
McMaster # MC218F75 are as smooth as a babies bottom on the face.
My luck varies FIXIT
 
markserbu said:
I went out to the plane to fly to breakfast with friends today and when I opened the hangar, I saw that telltale dark stain under the left main. So I caught a ride in the back of a 182 and took almost twice as long to get there. ;-) Next week I'll be putting the 4TH SET of brake pads on the left wheel in the 2.5 years since I've owned my RV-8A! The last two sets lasted 71 and 88 landings, respectively. The right set has been replaced once, and has lasted somewhere around 200 landings. I found out that the left master cylinder didn't have a strong enough return spring so I made a helper spring which seemed to cure the slight brake drag that I noticed from time to time, but maybe I need to make another one out of heavier wire. I've read the posts here about folks' brake life, and I'm definitely below the low end of the scale. My question for the gang: Has anyone gotten fed up with the terrible brake life and gone with another manufacturer like Beringer? If so did it make a significant difference? I'm perfectly happy to throw a few thousand bucks at the problem if it'll keep me from replacing brake pads every 70 or 80 flights!

As you can see in the pictures, the pads are worn but it sure doesn't seem like they're worn enough to hyperextend the piston and uncover the O-ring. And you can see that the O-ring looks brand new.

IMG_0418.JPG

IMG_0426.JPG

IMG_0427.JPG
Click to expand...
 
I would also use graphite on the 2 pins that hold the pads.
They can stick and drag.
Looks like rust on the pins.

clean pins with scotchbrite pad first.

Boomer
 
I'm reminded of the A&P I consulted about possible water in my sump sample.
He slurped it !!!, and said yes, it's water.

I guess the more 100LL you get exposed to, the more reasonable the idea of slurping a sump sample is?
 
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