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Looks to me like the tube welded under the axle window will do a fair job of reinforcing the place that sometimes cracks.
Maybe weld a plate on top also.
When I still had that swingarm, I made washers with a diameter a little larger than the swingarm sides, made one for the inside also, just had to shorten the spacer the width of the washer, inside washer was aluminum and about 1/4" thick, outside washer was stainless and as thick as I could use and still get the pin through the castle nut.
Those aftermarket adjusters won't fill the inside of the swingarm enough to help stop cracking because the shock mount will let them slide in, The important thing is that the adjusters are close to the same width as the inside of the swingarm tubes to prevent crushing the swingarm when the stack up is tightened, the large washers stop the damage to the axle widow area.
Washer will help to displace the axle head/nut pressure to the thinner wall tubing at the slots, but your still back to stiffer swing arm, that the less flex is going to cause the cracking to happen even faster.
Its the reason that HD went to the solid steel at the axle slot to solve the cracking problem in the first place on the older box steel swing arms..
So truth is, if someone where to make the end inserts for a 7/8" axle, would be better off just cutting the swing arms, welding in new inserts, then can play the added stiffener brace from there.
Or just mod one of the latest swing arms that are stiffer, to take a 7/8" axle and bolt up to the trans as needed.
Washer will help to displace the axle head/nut pressure to the thinner wall tubing at the slots, but your still back to stiffer swing arm, that the less flex is going to cause the cracking to happen even faster.
Its the reason that HD went to the solid steel at the axle slot to solve the cracking problem in the first place on the older box steel swing arms..
snip
So truth is, if someone where to make the end inserts for a 7/8" axle, would be better off just cutting the swing arms, welding in new inserts, then can play the added stiffener brace from there.
Or just mod one of the latest swing arms that are stiffer, to take a 7/8" axle and bolt up to the trans as needed.
snip
Washer will help to displace the axle head/nut pressure to the thinner wall tubing at the slots, but your still back to stiffer swing arm, that the less flex is going to cause the cracking to happen even faster.
Its the reason that HD went to the solid steel at the axle slot to solve the cracking problem in the first place on the older box steel swing arms..
So truth is, if someone where to make the end inserts for a 7/8" axle, would be better off just cutting the swing arms, welding in new inserts, then can play the added stiffener brace from there.
Or just mod one of the latest swing arms that are stiffer, to take a 7/8" axle and bolt up to the trans as needed.
Again that would require swapping wheel and rear brake and I didn't want or need to go that way. Modifying a newer style swingarm by cutting off the axle mounting blocks and making new ones to fit the 5/8th axle would also require machining new parts I don't have the equipment for. What I did is something I could do in my shop with the tools and equipment I have. As far as HD going to a stronger swing arm I believe it has more to do with the ever increasing weight of the bikes not the occasional cracking of swingarms that were designed in the late 70's for bikes that were never meant to be ridden that hard. Harley was content to build a bike that would cruise down the highway at moderate speeds and generally slow down for corners.
Last edited by bentparts; Jan 29, 2023 at 09:05 PM.
Looks to me like the tube welded under the axle window will do a fair job of reinforcing the place that sometimes cracks.
Maybe weld a plate on top also.
When I still had that swingarm, I made washers with a diameter a little larger than the swingarm sides, made one for the inside also, just had to shorten the spacer the width of the washer, inside washer was aluminum and about 1/4" thick, outside washer was stainless and as thick as I could use and still get the pin through the castle nut.
Those aftermarket adjusters won't fill the inside of the swingarm enough to help stop cracking because the shock mount will let them slide in, The important thing is that the adjusters are close to the same width as the inside of the swingarm tubes to prevent crushing the swingarm when the stack up is tightened, the large washers stop the damage to the axle widow area.
The only times I've heard of this cracking was if the bike had some type of lowering blocks attached to the shock mount. Once completely stripped my swingarm showed no signs of cracking or fatigue anywhere. The axle blocks that are rectangular from Drag Specialties I think, will work in my older swing arm, I've been using them for awhile now. Just requires a bit of filing down to fit past the shock mount. I did have to replace the studs with longer ones though.
Last edited by bentparts; Jan 29, 2023 at 08:56 PM.
I have to respectfully disagree about designed in frame flex on these bikes. IMO it was just Harley saying to themselves " good enough" when it came to handling. Also I don't know what kind of bagger your riding but in my bikes current configuration it weighs 719 pounds as measured at the truck scale near my home. Also, Not all twin cams have counter balancers, they were first introduced on the soft tail models which were not rubber mounted. since then counter balancers were added to many models. Personally, I've never encounter a cracked swingarm that didn't in it's past use lowering blocks.
To go the route your suggesting the trans mounting boss for the swing arm ( on my bike anyway ) would have to be bored out to 3/4 " as the swing arm mounting axle for my bike is only 5/8th". that isn't a good idea unless you remove the trans first and have very precise boring bits and maybe a boring machine. As far as adding vibration to the ride I'm not too concerned, the majority of the vibration is controlled by the front engine mount and swing arm mounts.
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