Sunday, March 29, 2009

March Madness: Replacing the Brake Pads

I don't get a lot of exercise. Sure, I play tennis, but only on the Wii. The same applies to golf and bowling: only the electronic variants meet both my inherent apathy and repulsive reaction to anything requiring physical effort. One thing I do like to do now and then, however, is to reach around and pat myself on the back when I benefit from my own often stunning prescience. After suitable stretching to limber up the atrophied muscles, of course. I've had plenty of occasion to celebrate my astuteness lately, what with the Rasmussen polls confirming everything that I believed we would see out of DC in the next four years, all compressed into less than 100 days. But, alas, this is a blog semi-devoted to my relationship with my RV-6, not my opinions on contemporaneous political shenanigans, no matter their import to the health and well-being of us all.

So, what exactly am I patting myself on the back for this weekend? Well, it is in response to my incredibly astute (if not financially efficacious) decision to keep Papa's annual inspection in the month of March, rather than move it two months further downstream to May as I legally could have. As in just about anything related to flying, it really comes down to weather management. There's nothing worse than a disassembled airplane right in the heart of flying season. As we all know, March comes in like a lion and out like a lamb, except when it doesn't. There's nothing lamb-like about the weather on this, the last weekend of March. In fact, this is the first time I think I've ever heard a weather phenomenon referred to as a "vigorous cold front." Cold fronts are never that fun, but "vigorous??" Oh my! That can't be good!

You may remember that one of the things I found during the inspection last week was a worn pair of brake pads on the right side. The left side was not as worn, but I decided to replace both sides this weekend. The aforementioned weather having left me no options other than to either stay home and make a nuisance of myself or go the hangar and do something productive, the choice was obvious. But, finding that making a nuisance of myself was not nearly as gratifying as I had hoped it would be, I ended up invoking option two.

Changing the brake pads is actually a very simple job, and I'm surprised that it isn't included in the list of things that store-bought airplane owners are permitted to do to their own airplanes as listed in Appendix A of Part 43 of the Federal Aviation Regulations. According to the regs, they're allowed to remove and replace safety wire and cotter pins, replace tires, and repack wheel bearings. Nothing is mentioned about the brakes. You have to remove at least one side of the brake calipers to get the wheel off to perform any of the allowable things listed above, so I'm not clear on the reasoning behind prohibiting the replacement of the pads as long as the calipers are off. It's really a quite simple operation, and interestingly does not even require the removal of the wheels.

With regards to safety wire and cotter pins, I should mention that the regulation specifically states the an airplane owner is permitted to "replace defective safety wire or cotter keys," so this may introduce a little bit of a Catch-22 unless there is no stipulation against the owner, you know, being the entity that rendered the safety wire or cotter pin defective in the first place. So as is usual with the FARs, the real rule is determined by enforcement cases rather than clear, unambiguous writing. Ambiguously crafted FARs are one of the crosses we bear as owners and pilots.

In any event, that kind of thing is moot for me since my airplane falls under the auspices of a much friendlier set of regulations. Section 1 of Part 43, paragraph (b) states that "This part does not apply to any aircraft for which an experimental airworthiness certificate has been issued, unless a different kind of airworthiness certificate had previously been issued for that aircraft." While that's not entirely a get-out-jail-free card, it is a get-out-of-paying-for-simple-work clause. And one of the simplest jobs on the airplane is replacing brake pads.

The first step in replacing the brake pads is to spend 10 minutes rifling through the toolbox looking for the special brake pad replacing tool. You see, the pads on an airplane brake are fastened to the calipers with rivets. It takes a special (but not overly expensive) tool to remove and replace the pads without incurring the risk of damage to the pads that you would have if you tried to manage the rivets with a hammer or other unsuitable blunt instrument. The problem with finding the tool is that there are a handful of removable pieces/parts that have a frustrating tendency to get separated from each other.

If you're clever, you stow the tool with all of those parts attached. As of today, I am clever. Last year? Not so much. It wasn't until this time, the fourth or fifth consecutive time that I've had to search for all of the parts, that I came across the brilliant (yet now, in retrospect, oh so obvious) idea of storing the tool as one unit. Better late than never, I suppose. Still, thinking back on all of those years of senseless, infuriating effort... Sigh.

If you follow that advice, the first step should be easy. You'll be happy to know that the second step is just as easy, albeit maybe a little bit shady in a strictly legal sense as detailed in my in-depth legal analysis above. Let you conscience be your guide. The second step is to willingly and deliberately cause the safety wire securing the brake caliper to become defective. This is accomplished by cutting it with a pair of wire cutters. Those are (or should be, anyway) easy to find, what with them being a single-piece tool. Just clip away the loops by the bolt heads and remove the wire. Just throw it away once you get it off of there since, from a legal point-of-view, it is now defective. Once the safety wire is gone, you can remove the two bolts that the wire was securing.

As you are removing the bolts, you will notice that the caliper feels loose, and you may be tempted to get all panicky and try to tighten it up. Don't panic; it's supposed to feel like that. The caliper slides on a pair of pins to allow it to snug up to the brake disk as the pads wear down. If the caliper wasn't sliding in the manner it's supposed to, you would have already had a mechanic look at your brakes because you would have been experiencing more pedal travel that you were used to. Note that you needn't remove the bolts entirely; they are threaded into the outside caliper half. You will want to make sure you're ready for the outside half to fall off when you remove the bolts. It's not the greatest picture, but you should be able to see the gap as the pad is moving away from the brake disk. I just leave the bolt heads flush and let the screw action push the pad away. If you choose to do that, though, you might have to alternate between loosening the top and bottom bolts every few turns so you don't put a lot of bending torque on the pad. You'll see what I mean.

Once the outside pad is removed, you can slide the remaining part of the caliper assembly off of the slide pins to remove the other pad. This should be done with great delicacy if your airplane, like mine, has rigid brake fluid lines. There are two very preferable things at play here: you would prefer not to break the brake fluid line, and you would also prefer to not remove the fitting. The ramifications of breaking the line should be obvious. The consequences of removing the fitting may be the need to later bleed any air introduced into the brake system back out of the system. If possible, it is best to just carefully move the caliper off of the pins and slide the inside pad off.

Once both of the pads are off, it is time to use the brake pad removal tool that you spent so much time looking for in the first step. In preparation for the rivet removal, take off all three of the pieces/parts that you installed if you are using my patented storage method. If you are still insisting on storing the parts separately in support of some kind of masochistic "thrill of the search" fetish, you are ready to move on to the next step. Find the pointy part and attach it to the end of the threaded rod. Leave the bottom hole open.

Put the tool in a vise and clamp it down. Place the brake pad into the 'C' part of the tool with the smushed up part of the rivets facing up. Slowly screw down the threaded rod until the pointy bit is nicely centered and seated on the rivet. Slowly screw down the threaded rod while holding the pad in place. The idea is to use the pointy part to push the old rivet out. As the rivet pushes out, you will feel a notable lessening of the resistance to the turning of the handle. You may also hear the old rivet fall out and hit the ground or workbench, but if not you can just reach up under there and remove it. You can keep screwing the threaded rod through after the rivet has popped out if you want to, but it's a bit of a waste of time. Now me, I was looking for an excuse to be out in the hangar for as long as possible, so a little wasted time was just fine by me. But even with that being the case, I thought it a silly thing to do, so I just backed out the rod and moved onto the next rivet. Again, if you aren't trying to kill time, go ahead and remove the pad from the other part of the caliper right away since you already have the tool configured for it.

Once both pads are removed, or if you are a linear thinker and prefer to dress in a one-sock-one-shoe process rather than a two-socks-then-two-shoes manner, you need to reconfigure the tool for putting the new rivets in the new pads. Just pull off the pointy bit and replace it with the conical thingy. The other part just drops down into the open hole at the bottom of the 'C'.

Line up the new pads on the caliper halves and drop new rivets down into the recessed holes in the pads. I put all three rivets in rather that doing them one at a time to ensure that I don't rivet a pad in crooked and find that I can't get the other rivets in. This is a bit tricky, though, because the pad has to be turned over to fit it into the tool. This can (and often does) result in anywhere between one and three rivets falling out. As you can surely imagine, this is not a desirable turn of events since rivets, much like the disparate parts of the brake tool, are absolute masters of camouflage. They look all bright and shiny and you'd think they'd be easy to find, but take my word for this: you do not want to drop them.

I usually start with pressing the center rivet. This lets me contort my fingers such that they are holding the other two rivets in place. What you're trying to do is get the bottom part of the tool to fit up into the recessed hole at the bottom of the pad while you screw down the conical thingy to press the rivet into place. I could write a thousand words about this, but I think these pictures might show it better:

Voilá! Snug them down tight, but not too tight. (Hey, I know that's ambiguous and arbitrary guidance, but I was reading Federal Regs just a few paragraphs ago - it's contagious!):

Now it's simply a matter of replacing the brake pieces back to where you found them.

And, of course, replacing the defective safety wire:

See? This was a lot easier than jacking the plane, rendering safety wire and cotter pins defective, removing the wheel, deflating the tire, splitting the wheel, removing, cleaning, and repacking the wheel bearings, and reassembling the whole mess. (In other words, the very things that the FAA has deigned to allow store-bought airplane owners to legally do by themselves.)

I know this to be true because I did all of that other stuff yesterday too. The brake work takes about half an hour per side. The removal and repacking of the bearings took at least an hour per side. I simply cannot understand why Part 43 allows one but not the other.

See what I mean?


  1. By the time you get annual done the weather will be better and you can have fun again.

    By the way, I trust you took the opportunity to rotate the tire. When servicing the brake pad, I don't have your special tool. But, I have a set of die for my rivet squeezer to set the new rivets. After drilled out numerous rivets during my build process, I can drill out those rivets pretty easily. No special tool needed.

  2. hey thanks for the write up. i really enjoy your blog and check back in often. as for you first paragraph i was laughing myself silly this morning about a corner and paint and a certain someone who wasted tons of money and now thinks that auto companies maybe best just to go bankrupt. can you say hated by all. ah well it would be funnier if it was not our money.

    as for your second paragraph, i said to my self "stay home" and then bam! nice i was laughing again. maybe i am just in a good mood.
    if you don't ask about my hopes for the 3 i will not ask about the row boat.

  3. Thanks Leon. I wasn't sure anyone would actually read this one, even though I tried to make it entertaining. And of course these days it's risky to even breath a hint of politics into anything, but in this case I think an "I told you so" was appropriate. After all, I don't think it would have been significantly different if the other guy had won. Congress has a 14% approval rating for a reason.

    About the canoe: it's still down in the basement waiting for me to build a fire pit in the back yard. So is the porch swing. The problem is that I don't trust my abilities enough to buy the expensive wood that these things require. In the case of the canoe, that was a good decision as I was unable to make the precise cuts needed for it to for fit together tightly enough. The porch swing looks a lot better, but when I did a test sit, I heard the wood cracking. That's not good at all; I'm not very heavy! I think I work best from a kit - the kayak is a work of art!