Unexpected braking

Today I had my most interesting landing in my RV-8 so far... .

When I touched down I had a substantial amount of breaking power on the left wheel. Now the break didn't completely lock (at least I couldn't find a spot on the wheel afterwards) but it did break enough that I needed full right rudder and quite a bit of right break to keep my RV on the runway. After I took the wheel pans off the left break pad/assembly was very very hot and even though the left break pads are still there they are worn down below minimum now. The right once still have a long way to go have about 80 hours on them. I could loosen the pads again to have the wheel go free by wiggling the break pads after they cooled down.

Couple of more clues:

- I am using Van's standard Matco wheel assembly/ standard cylinder
- Yes I am sure I wasn't on the left break when I touched down... .
- I did practice spins for 30 minutes or so before I landed. Now the reason I think this is important is that I spin left. To get in a spin you "kick" the rudder which is nearly impossible to do without "kicking" the break the way the break "pedal" is attached to the rudder pedal. Now this should build up substantial pressure on the breaks but I would think that pressure would be released when the rudder pedal goes back to neutral... . This is also not the first time I am doing spins... .

Now my question is what could cause this? I of course will replace the break pads but what else would you check to make sure this doesn't happen again.

Thanks

Oliver
p.s. I think I was lucky doing a low energy 3 point landing. Never knew how short you can stop an RV-8 without putting it on the nose... .

Did you look at the windsock? Was mighty x-windy at Solberg around noon

Just kidding wondering what was the cause of unexpected braking...

Tire pressure?

This may be a dumb question, but is you tire pressure ok in the left tire?

Vlad said:

Did you look at the windsock? Was mighty x-windy at Solberg around noon

Just kidding wondering what was the cause of unexpected braking...

Click to expand...

Was actually flying around 7pm. Barely any wind left.... . As I was basically pumping the left break in the air doing the spins I am wondering if somehow the pressure didn't fully release.... .

jpowell13 said:

This may be a dumb question, but is you tire pressure ok in the left tire?

Click to expand...

Haven't measured it but looks "normal". Will measure it next time at the airport. Not sure though how low tire pressure would wear out the break pad. My first thought when landing was I blew a tire but as said visually looked the same as the right tire before and after.

Well, if it wasn't dragging when you took off, it would stand to reason that something happened afterwards that caused the brake to stick. Have you checked the brake pedal for free movement? Is there any chance that all that left boot while performing spins may have caused any one of those brake pedal components to bind or stick? And 80 hours on a set of pads doesn't sound old to me, so I'm thinking the wear was caused by this incident.

If it were me, I'd climb under the panel and wiggle that left brake pedal to see if I can replicate a binding condition. Double check the bolts, washers, and cotter pins, check for scraping, etc. If you have brakes for the back-seater, check those as well.

Let us know what you find.

Pads

Your message implies that the left pads were worn considerably more than the right pads. Did I read this correctly? If so this obviously didn't happen on one landing. It's a simple hydraulic system. If the left pads are wearing evenly (inside and outside pad), but considerably faster than the right side, it would seem that the pressure isn't releasing. If it were mine I would be checking the entire left side. Could be the master cylinder, the caliper or a restriction in the line acting as a one way valve.

Maybe I misunderstood your post. Not sure.

You broke your left brake?

DaAV8R said:

Your message implies that the left pads were worn considerably more than the right pads. Did I read this correctly? If so this obviously didn't happen on one landing. It's a simple hydraulic system. If the left pads are wearing evenly (inside and outside pad), but considerably faster than the right side, it would seem that the pressure isn't releasing. If it were mine I would be checking the entire left side. Could be the master cylinder, the caliper or a restriction in the line acting as a one way valve.

Maybe I misunderstood your post. Not sure.

Click to expand...

The left pad certainly are woren substantially more and inside and outside do wear even. I haven't measured it yet precisely but it looks like the right side has 2mm or so of the notch which indicates minimum thickness showing on the left side the notch is gone.

Will take things appart and see what I find. I am a bit puzzled to why I never noticed it before though. If this has been going on for a while it certainly never did what it did yesterday before but I also don't recall needing constant right rudder on taxi.

Oliver,
Completely agree with the previous post that this didn't happen in just one landing. For the pads to be worn that much different would happen over time.

Check and see if the left master cylinder piston is returning. IF it is depressed, even slightly, it can have enough residual pressure to apply the brakes. (had this happen during a practice at Charlotte in the old NASCAR days. NOT funny. Could NOT move the car. Thanks to Tony Eury SR. and Dale Earnhardt SR. for the tip. Never forgot it.) Tom

Found this thread:

http://www.vansairforce.com/community/showthread.php?t=23560

Post #9 seems quite related.

So from this and what others commented in this thread a consistent theory would be that my break pads are wearing unevenly and more quickly then they should. When the left one dropped below minimum and I kept pushing it hard during my spins the puck got stuck closed in the caliber housing which caused the event yesterday.

Will see if I can find evidence of that when I go to the airport.


So if this is correct the real question to answer is why are the breaks wearing unevenly.

I had uneven wearing on my brake pads. After examining every component in the system, I found that one of the master cylinder pistons was not returning 100%. Less than a 1/8?. I put return springs on and the uneven wearing stopped.