By Vic Syracuse, EAA Lifetime 180848
This piece originally ran in Vic’s Checkpoints column in the February 2021 issue of EAA Sport Aviation magazine.
Last month I promised I would help you change your tires and brakes, so here we go.
Safety is paramount. The aircraft will be on jacks, so if you haven’t done this before, you might consider getting help. There are a number of jacks on the market that work on various types of aircraft, so use the one that is best for your aircraft. Once the aircraft is on the jacks, be careful when moving around it so you don’t knock it off. The first thing you do after the tire is off the ground is deflate the tire using the valve stem removal tool. This is a safety precaution, in case any of the wheel bolts are sheared and the wheel is being held together by the axle nut.
Next, you will have to remove the brake caliper(s), which are usually held on with two bolts and may be safety wired. Then remove the cotter key from the axle nut. I always mark the location of the cotter key hole and count the number of turns it takes to remove the axle nut. That will help in reinstalling it later because sometimes it can be a fight to locate the cotter key hole. Once the axle nut is off, the wheel can be removed from the axle. Some wheel assemblies have spacers on the axles, so be sure to pay attention to their locations when removing the wheel. I keep my phone handy as a picture is definitely worth a thousand words here.
Now, take the wheel assembly to the bead breaker and break the contact of the tire to the wheel prior to removing any of the wheel bolts. Once that is accomplished, remove the bolts and then pull the wheel halves out from the tire. At this point, I will also remove the wheel bearings and place them in a solvent to break up the grease while I mount the new tire and tube. Keep track of which wheel bearing goes with each wheel half and replace them into the same wheel upon reassembly.
Notice I said new tire and tube. I always replace the tube whenever I change a tire. To me, it is just not worth risking having to redo this process by reusing a tube. Tire tubes can be misaligned while inflated inside a tire and sometimes even chafe and rub, creating a weak spot. Reinstalling them in a different tire can allow that weak spot to fail. By the way, spending more money on high-quality tires and tubes to me is worth the cost. For those of you who have wheelpants, leak-guard tubes with a 90-degree stem are worth the extra price, as they usually only require adding air once or twice a year.
The first step in reassembly is to liberally coat the new tube with talcum powder prior to inserting the tube in the new tire. This will allow the tube to freely expand and move around inside the tire as it is inflated. Make sure you place the tube inflation stem so that it is located in line with the red dot on the tire. This is important to help with balancing the whole assembly. Next, carefully inflate the tube with just enough pressure so that it takes a nice, round shape inside the tire. Don’t inflate it too much or it will be very difficult to get the wheel halves together.
Now, insert the cleaned wheel halves into the tire, paying close attention to the tube so you don’t pinch it as you push the two halves together. You should be able to hear the sound of metal on metal. If not, you want to back off and try again. Again, be sure to have the tube coated really well with talcum powder. It will help the wheel halves slide past the tube.
If that feels goods, add the brake disc, insert the bolts, and tighten them according to the proper torque specs. Sometimes, that number is printed on the wheel but wears off over time. As the aircraft ages, you might also check the brake disc for minimum thickness as specified by the manufacturer.
Cleaning the wheel bearings can be done in multiple ways. Use commercially available wheel bearing cleaners or clean by hand with spray solvents such as Brakleen. It is very important to make sure all of the old grease is removed. Then, dry them out using low pressure compressed air, being careful not to spin the dry bearings. Repacking can also be done in multiple ways, and some manufacturers specify a particular brand and grade of grease. AeroShell No. 5 or Mobil 1 are good choices. I like Mobil 1 or synthetic boat trailer grease for wet operations, like grass runways and amphibians. No two ways about it, repacking the wheel bearings is the messiest part of this process.
The next step, wheel assembly balancing, is not critical. However, it makes for smoother taxis and less vibration after takeoff as the wheel spins down. It’s a quick procedure using a motorcycle wheel balancer, giving only a static balance, which is usually sufficient. I have found that some of the higher-end tires don’t even need to be balanced, with most of the others requiring less than an ounce of lead weights. Automotive stick-on weights work perfectly for this.
All that’s left now is to reinstall the whole assembly on the axle. The majority of the time the axle nut will line up with the cotter key and the wheel bearing preload should be correct. But if it takes channel lock pliers to tighten the axle nut in order for it to line up, then the bearing preload is way too tight and you may need to drill another hole for the cotter key. A little bit of drag on the wheel assembly is okay, as it will not spin really freely due to the wheel bearing grease. Some bearings have a rubber exterior seal on them. It is important to make sure that the rubber seal isn’t turning when the wheel is spun. This usually requires a little tighter setting on the axle nut.
The last thing is to reassemble the brake caliper. You did check the brake pads first, right? If you don’t have the tools to replace them, give them to your friendly A&P mechanic. It only takes a couple of minutes to drill off the pads and replace them with new ones with the correct tools. Don’t forget to safety wire the brake caliper bolts or, as we have been doing, use Nord-Lock washers. Do take the cap off the brake reservoir and check the fluid level. If you have been adding fluid as the brakes wore down, the reservoir will now overflow as you push the caliper piston back in when replacing the new brake pads.
Once completed, with your new tires properly installed and balanced, taxiing will be noticeably different. Don’t forget to break in the brake pads according to the manufacturer’s recommendations. Usually after three or four landings, the pads will feel normal.
Now, go have fun!
Vic Syracuse, EAA Lifetime 180848 and chair of EAA’s Homebuilt Aircraft Council, is a commercial pilot, A&P/IA, DAR, and EAA flight advisor and technical counselor. He has built 11 aircraft and has logged more 9,500 hours in 72 different types. Vic also founded Base Leg Aviation and volunteers as a Young Eagles pilot and an Angel Flight pilot.
