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  • Steve

RV-8 and the 2024 Condition Inspection Part 1

The weekend of 3/2 and 3/3 2024 was supposed to be the kickoff of my 2024 Condition Inspection. I do a progressive condition inspection so I don't have the airplane down for a long period of time. I do one section, put it back together, fly it, do any section, lather, rinse, repeat.


Saturday I was going to start on the landing gear since I installed new tires last February. Last year the left brake disc was down to .1697 with a maximum wear dimension of .167, so I was getting close. I ordered a pair of the APS PMA brake discs (P/N APS164-01700) to try them out. The genuine Cleveland parts are pretty spendy and the Rapco alternatives are questionable, to me, but these seemed like a good compromise. They were out of stock at Aircraft Spruce and it took about 6 months to get them, so it is a good thing I didn't need to change them right then. The plan was to do it this year.


After pulling off the wheel pants, I started by checking the thread depth on each tire. In the past, the left tire has worn much faster than the right. This has led me to change tires before I was really ready to in the past because I wasn't watching close enough and one wore too thin to use while the other still had quite a bit of tread left.

Right wheel and tire assembly.

I was planning to rotate the tires (right to left and left to right) in about September and do so at least twice a year in an effort to even out the wear between the left and right tires. When I checked the tread depth at that time, they were nearly identical and there was no real abnormal wear, so I left them alone.


When I checked the tread depth again today, it was still pretty close. The left tire had 4/32 tread depth left and the right was about 4.5/32. Pretty close. Even though they were close I was planning to swap them anyway just to try to even things up. The inside tread which doesn't wear very fast was about 6/32 on both sides.


It is pretty easy to swap the tires since I have a spare wheel and tire that I can throw on while I remove the other side (only jacking one gear leg at a time). That wheel is left over from my old Cessna 150. It is pretty well corroded and that's why I replaced it all those years ago, but it has a little life left in it.

Spare wheel used for swapping.

Once I got the left wheel and tire off and over to the workbench, I took the wheel apart to get the brake disc off. Just for giggles, I measured the remaining thickness and it was at .1685. Worn a little from last year, but still within spec. For reference, the new one measured .1905.


Once I got everything cleaned up and ready to go back together, it became immediately obvious that something was wrong. The new disc wouldn't seat all the way down in the wheel half. It stopped about 1/4" from the bottom. For once, I didn't pick up a hammer trying to make it fit. I pulled it out and took a closer look and it looked for all the world like it was shorter than the one I took out.

Left wheel with old brake disc.
The new disc is to the left of the tire.

Can't quite tell, but those don't look the same to me.

One of these things is not like the other.

Upon taking some measurements, it became quite clear that the new ones were not like the old ones.


Length of original disc.

Length of the new disc.

Nope, definitely not the same, the new one is about 3/8" shorter than the old one.. Now I'm really upset because a relatively simple task just took an unwelcome turn. I have no real choice but to put the wheel back together with the old disc. I didn't know exactly what happened at this point. Did I order the wrong part number? Did I order the right part number but ACS sent me the wrong part number? Did I order and receive the right part number but the wrong part was in the box? Who invented liquid soap and why?


At this point, I probably have a year of use left on it. I put 80 hours on them since installing the new tires last February. I'm pretty sure they will last another year at this wear rate. I also measured the pads, wondering if they needed to be replaced. Just judging by the depth of the rivets, it looked like they were pretty close to what they were last year. The minimum thickness for the pads is .100", the ones I had were at .165".


So, the big question is, do I just clean and inspect the right wheel and tire and call it good for this year, or do I wait and get the new discs and put them on this year? I left the airport to be able to do some research and try to figure out what happened.


Unfortunately, it looks like I ordered the wrong part number last year. I don't know how I came up with that part number (APS164-00400). I looked through my order history at ACS and it looks like that is what I ordered, so it looks like, once again, the only person to blame is me. I hate it when that happens.


The only thing that I can figure out is that I looked at the parts breakdown for the Cleveland 500 X 5 wheel assembly and just went with the most common disc part number. I have a 40-78B wheel assembly and the 164-04000 disc is applicable for all of the Cleveland 5 inch wheels except for the 40-78, 40-78A, and 40-78B. Go figure.


The table that I have from my 2020-2021 printed ACS catalog is different from the one currently online. It is clearer in the catalog online.

We are interested in Item 6, Brake Disc.

The correct part number is clearer on this chart than the one I used.


The more I think about it, the more I think that I will just clean and inspect the right wheel / tire / brake and let it go until next year. I ordered the new, correct discs and should have them on hand in case they are needed sooner.


I've asked Aircraft Spruce if I can return the wrong ones since they are untouched, but I have probably waited too long to be able to return them. I guess I will put them on Barnstormers and see what happens.


This isn't the first time I ordered the wrong part, and I am not the first one who has done it, but it still irritates me (it irritates me more when I do it than when others do it). Most of the times I did it was at work so I didn't have to pay for both, it is much more annoying when I do it for my airplane that I have to pay for it and wouldn't you know it, the ones I need are a little over $30 each more than the ones I bought.


If you read this and it keeps you from making the same mistake, it might, and I say might, make the whole thing a little less irritating. Oh, if you are in the market for a pair of brand new, never been used APS164-04000 brake discs let me know, I'll make you a good deal.

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