Harley Rear End Sway (Bagger Sway)

OK, big Harleys (like my 04 Road King) have the swing arm pivot bolt attached to the frame like almost every other motorcycle. But, Harley used rubber bushings to give it the plush ride. Nice ride, but it also means the rear swing arm can get deflected, creating a nice wallowing wiggle in turns some times.

As is typical of motorcycles, the rear of the transmission/engine is hung on that bolt. It works. The swing arm has two bearings out at the ends, and the engine/transmission sits in the middle in between these points.

Now this is where things get weird.

The "fix" everyone uses for this wallowing wiggle isn't to use stiffer bushings where the swing arm bolt mounts to the frame, but is to use a turnbuckle to lock the rear of the transmission to the frame. The claim is that by preventing the transmission from moving side to side, you effectively lock the sway arm in place and eliminate the wobbling.

To me, this seems like placing the cart before the horse. Especially since the only way I can see this working is by having the swing arm grinding against the transmission case. The transmission was never intended to hold the swing arm in place. Not saying this doesn't work, it seems it does. Just that it seems like a darn poor way to do it. Especially since the only way I can see it working is to have the swingarm grinding against the side of the transmission case.

Ask about this on a Harley forum or two, and about all you'll get is that Buel did something like this (he did) and Harley used a setup like this on the Sportster (they did), therefore it's a perfect fix. But it manages to fail to notice that in these two cases, the swing arm really is mounted onto the transmission, and not the frame (interesting design btw). In that case, everything is made to do this job, complete with bearings and such.

Some of you folk are Harley nuts and motorheads. Maybe you could explain to me why these transmission to frame turnbuckles really are a better "fix" than stiffening the rubber frame bushings of the swing arm pivot bolt?

It's not so much that the rear fork (HD's actual term for swing arm) is moving in the bushings of the transmission. It's that the whole assembly - engine, trans and rear fork - can move laterally, as well as up/down/all around, in the frame. This is done for two reasons; to keep the drivetrain in alignment and to help isolate vibration. By adding the turnbuckle, that lateral movement is eliminated, while still allowing the motor to move up/down/all around.

I'm not entirely familiar with the pre-'09 frame, so I'm only assuming the only hard mounting point is at the top of the front cylinder, the rest being rubber isolated. That's why the rear end can swing.

How did they fix this in the 09+ frame? Because that at least when I rode one did have any real sway.

Ah, hadn't thought of chasing the drawings of the 09 and later redesign. That helps clarify some things.

The HD parts drawings are misleading on the 04, but clarified on the 09. There are active bushings in between the swingarm and the transmission. It's apparently a tight fit, and this is why the engine/transmission/swingarm are regarded as one unit. You really can't figure this out looking at the 04 parts drawings, or service manual for that matter. The bushings and swing arm bearings and such are the same between the 04 and 09, so there was no change.

The rubber bushings where the swing arm bolt goes through the frame are different between 04 and 09. Doesn't seem radically different, but different none the less.

Front motor mount and top motor mount are completely different between 04 and 09.

The stabilizer links/kits are sold for the 09 and later bikes. Slightly different because of the changes in the frame and such, but fundamentally the same. I can see why as the rear doesn't seem to be held really any differently than the earlier models were held.

But, now that I better see how Harley built this thing, I better understand why the stabilizer is a reasonable tool. The swingarm (ok, rear fork) does indeed ride against the rear transmission, through the bushings. So, holding the transmission in place would hold the swingarm in place. You could do a panhard rod to the swing arm, but that would involve welding. Using the transmission housing just involves bolts. OK.

So, at worse, using the transmission to hold the swingarm in place would accellerate the wear of the bushings. It would not grind right up against the transmission housing.

Still not sure that stiffer bushings for that swing arm pivot bolt is as good or perhaps better than using the turnbuckle. But I do better understand the turnbuckle.

Complaints about increased vibration do seem to exist for all the various stability thingies. Inconsistent, with some folk saying they get it, others saying they didn't.

If you look carefully at dirt bikes, the swingarm bolt goes through the frame outer rails, then through the back of the engine cases and in some designs through plates welded to the frame 'backbone'. It's done that way to keep the swingarm in alignment with the rest of the bike on acceleration. XR600's are particularly bad about the left frame tube flexing on acceleration, leading to a very weird rear steer. I know my XR600 did that bad on whoops.