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[Chief]

With the frame swap going on, I'm in a good place to shed some light on the swingarm on our Ultras and Road Kings. Currently, one of the hottest aftermarket parts out there are the many different stabilizers designed to improve the handling of the FLH series of bikes.

Hopefully these pictures will help site members see just how the rear end of the bike goes together and they can understand just what the stabilizers will and won't do.

First, the parts...

This is a shot of the rear of the FLH transmission with the swingarm directly behind the shaft. On the outermost ends of the pivot shaft you have the large rubber mounts, more about them later. Inside of the rubber mounts you can see the outboard spacers. Just inside of that you can see the shiny surface of the inner spacer. The swingarm bearings (not shown) go on the inner spacer and are then pressed into the swingarm. That's all the parts there are to the rear swingarm. It's pretty simple.

[Chief]

Another shot of the parts.

[Chief]

This is where the swingarm bearings will be installed.

[Chief]

Here's where the pivot shaft sticks through to the left side of the transmission.

[Chief]

Here's the shaft installed.

[Chief]

Inner spacer (no bearing) installed on pivot shaft.

[Chief]

Here's the outer spacer slipped on.

[Chief]

And the rubber mount with optional Sta-Bo bushing (more on that one later too).

[Chief]

Ok, that's all good, but why is there so much talk about 'rear steer' or 'rear wobble' and all the other problems.

Here's the problem. This is how the swingarm pivot mounts into the rear of the frame. The rear of the engine, the swingarm and everything else is held into the frame with the big rubber mounts. That's it. There is no other mechanical connection between any of the drive train components at the rear of the motorcycle.

Looks kind of flimsy huh?

[Twolanerider]

Chuck's powder coated frame is home .

[Chief]

Here's a close-up of the left side.

So what's the problem and what's the solution?

The problem is very simple. When a sideways load is placed on the rear wheel, this force pushes the swingarm to the side and there is nothing but these big hunks of rubber to keep everything located properly. The rubber mounts flex and let the swingarm move side to side, causing rear steer.

The problem with the rubber mount rear end is the rubber mount itself. The big rubber donuts flex under load and allow the swingarm to move sideways when a sideways force is applied to the rear tire, like when you are in that sweeper at 80 mph.

How do you fix it? Simple. Come up with a way to keep the swingarm from moving side to side.

[Chief]

Here are some more shots of the rear pivot shaft in the frame notches.

[Chief]

Since the problem of rear steer is caused by lateral movement of the rear of the motor, I belive the simplest way to correct it is to prevent it at the source, the pivot shaft. This is why I chose the Sta-Bo bushings over all of the other stabilizer brackets out there.

Most people hear 'bushing' and think about bushings like those found in car suspension systems. These bushings are not designed to work that way at all. The Sta-Bo bushings are designed to stiffen the rubber mounts laterally and prevent the flex in those parts. The Sta-Bo bushings are the only product out there fixes the problem where it starts.

The Sta-Bo bushings work by providing a bearing surface to absorb the lateral forces produced by cornering loads and prevent the swingarm from moving sideways. The bushings simply fit inside the void of the rubber mount and rest against the metal plate in the bottom of the mount. The outer edge of the Sta-Bos rest against the inside of the swingarm pivot mounts. This effectively removes any sideways movement of the swingarm and the pivot shaft. Through all of this, the transmission isn't the problem, but is just going along for the ride.

Vibration. All of these devices that provide a more rigid connection between the swingarm and the frame increase the possibility of extra vibration. This is to be expected. By installing one of these devices, you're eliminating a mode of isolation by eliminating the movement of the rubber mount.

In the end, I feel the trade-off is worthwhile.

[Chief]

Chuck's powder coated frame is home .

Who spilled the beans?

[twojay]

Since the problem of rear steer is caused by lateral movement of the rear of the motor, I belive the simplest way to correct it is to prevent it at the source, the pivot shaft. This is why I chose to get the Sta-Bo bushings.

Most people hear 'bushing' and think about bushings like those found in car suspension systems. These bushings are not designed to work that way at all. The Sta-Bo bushings are designed to stiffen the rubber mounts laterally and prevent the flex in those parts. It is a very simple fix.

The Sta-Bo bushings work by providing a bearing surface to absorb the lateral forces produced by cornering loads and prevent the transmission from moving sideways. The bushings simply fit inside the void of the rubber mount and rest against the metal plate in the bottom of the mount. The outer edge of the Sta-Bos rest against the inside of the swingarm pivot mounts. This totally removes any sideplay. No sideplay means the transmission can't move sideways and the rear wheel stays inline with the front.

Vibration. All of these devices that provide a metal-to-metal connection between the transmission and the frame increase the possibility of extra vibration. This is to be expected. By installing one of these devices, you're eliminating a mode of isolation by eliminating the movement of the rubber mount.

In the end, I feel the trade-off is worthwhile.

Hey Chief, Glad to hear that you are happy with the new powder coating. Looks awesome to me. I have the sta-bo bushings and the tru track on my bike. I noticed the increase in vibration that you referred to here after installing the bushings and have considered removing them. With the tru track do you think that the sta bo bushings are needed? tia, jj.