When overhauling the wheel bearings of my H-36 some years ago I found that the bearing seals were totally ineffective. The Cessna felt seal and support washers were in place but the internal diameter of the seal was 0.125” larger than the steel collar on which it was supposed to bear, thus leaving an air gap all the way around the bearing where water, dust & mud could enter. This clearance was undoubtedly the cause of our bearing failures, especially in Australia’s dusty airfield environment. Hoffman were not interested in this problem so we solved it by removing the Cessna felt seal and alloy washers and substituting a neoprene automotive seal with the same outer diameter but with a smaller internal diameter which matched the steel collar. The seal is a readily available size & is commonly fitted to trailer & caravan wheel bearing hubs. Other Australian operators addressed the problem by retaining the original felt seals & washers but replacing the steel collar with a new one machined to the correct outer diameter to fit the original felt seals. Either approach works quite well, but if you decide to make new collars ensure that you add a small chamfer both sides of the internal bore of the collar to ensure it bears only on the flat bearing faces.
Hope this helps J G Viney. Dimona Lisa VH-GVQ From: [email protected] [mailto:[email protected]] On Behalf Of Michael Stockhill Sent: Monday, August 17, 2015 12:58 PM To: [email protected] Subject: Re: [DOG mailing list] Removing wheel axle Reviewing the H36 parts book that I have, the drawing of the wheel/axle/brake assembly is very small scale, with few callouts for parts. One thing that is evident is that the axle nut and lock washer are on the outside of the wheel fairing. In the two aircraft I maintain, both had the axle nuts inboard, with the axle inserted from outboard, resulting in interference of the axle nut and lock washer with at least two of the four attachment bolts that secure the brake mechanism mounts. While it may be "prettier" to have the axle nuts inboard, it is probably best to go with the configuration shown in the parts book. In my instance, I thought of reassembly that way, but elected to use the countersunk screws as a minor alteration, which we can do in this country as mechanics if we are brave enough. Besides the four attachment bolts, there are an additional four securing a flange for the floating brake caliper. On one or two of the four brakes I worked on, these had to be loosened or removed in order to provide clearance for removing the caliper. Each caliper is located by two rods of about 7/16 diameter and an inch or so in length. If the rest of the wheel assembly is corroded, it is probable that these are also corroded. They can and should be cleaned and polished. The outer portion of the bore on the cylinders is also likely to show corrosion. It is a judgement call, but I am usually comfortable with cleaning up that corrosion with Scotchbrite or similar products. Best to avoid steel wool as particles will embed in the aluminum of the cylinder. Pistons can similarly be salvaged. Braking action is significantly improved when this corrosion is cleaned up. Removal of the bearings from their spacers may necessitate fabricating a tool for a press or bearing puller. If I recall correctly, the ID of the bearings is 31 or 31.5 mm, and the axle is 30 mm diameter. The spacers have a shoulder on them. A tool would have similar configuration, with an OD of 31 or 31.5 mm, and a shoulder, with an OD of 30 mm. Problematic was getting all the air bubbles out of the brake lines when bleeding them (best done from the bottom). There is a flexible aircraft hydraulic hose or line downstream of the master cylinder that can trap air bubbles. Another more gifted Dimona mechanic told me that raising the tail can often cause those bubbles to be displaced. This worked for me on both aircraft, with the tail raised about three feet or so. Surely clean up any corrosion on the inside of the axles. And think of the next guy when reassembling, using Boeshield or similar products for corrosion control and maybe antiseize materials. If all else fails in attempting to remove the axles, consider that Lycoming's technique for removing seized sparkplugs is to make a funnel over the sparkplug and chill it with a blast of CO2. One could probably shoot CO2 through the bore of the axle and shrink it away from the spacers! MLS On Sun, Aug 16, 2015 at 6:00 PM, Michael Stockhill <[email protected]> wrote: A revisionist thought. If the axle is truly seized, it is likely to be seized on the the sleeve/carrier assembly for the brake caliper as well as the opposing bearing carrier tube. It may be best to leave it unloosened until the axle has broken free. Sorry for the poor thinking on my feet today. I should get out the parts book to refine my terminology. MLS On Sun, Aug 16, 2015 at 5:48 PM, Michael Stockhill <[email protected]> wrote: Yes, those will have to come out eventually. I would just loosen them until you get the axle out. I did find during reinstallation that if I tightened them before everything else was assembled, that the axle would bind at insertion. If anyone else has done brake and tire work on the aircraft previously, you may find that the holes in the brake attach plate have been elongated--it looks like during reassembly someone didn't get proper alignment and just went after them with a drill bit. . On both of our ships, that was the case. Going to the slightly oversize 1/4 inch countersunk machine screws (vs 6 mm bolts) mitigated that a bit. Keep track of which brake assembly goes on each side of the ship. Photos tomorrow. I took advantage of good WX to fly my PIK 20E for a couple hours, and did the shuffle/dance to drag my Aztec out of the hangar for test flight after maintenance. Cheers, On Sun, Aug 16, 2015 at 5:36 PM, Nils Beck <[email protected]> wrote: Did you also remove the 4 bolts that attach the brake to the wheel fairing? Best regards Nils Beck On 16.08.2015 14:18, Guy Audenaerde wrote: My Dimona H36 Mk2 ser. 36267 build in 1988, equipped with Sauer S2100-1ss1 has 4550 hours on the airframe. It is three years in my ownership and i suspect that the maintenance of the main wheelbearings is urgently due. When i jack up the wheels and rotate the wheels they emit a "grinding" noise and have a lot of play. Question: can someone give me a detailed procedure for removing the axle and overhauling the wheelbearings. I removed the locking nut on the outside of the wheelfairing but did not succeed in getting the axle out of the fairing, despite carefull tapping on the extremities with a hardwooden block. 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