Installing A Dirty Tail Kit

Article and Photos By: Chris Callen

Originally Published In The April 2020 Issue Of Cycle Source Magazine


In the year nineteen hundred and eighty four, the Harley-Davidson motor company would revolutionize the custom culture surrounding its product with the first FXST, Softail. This bike would combined the classic look of the hardtail frames with no visible shocks and still provide some shock absorption from hidden, under frame suspension components. That bike coupled with the Evolution motor drove the popularity wave that grew the company and saved them from obscurity.

Over three decades the poor old Softail has gotten somewhat of a bad wrap, at least those early models. They are seen as heavy and clunky in the back end and get a “middle chair” from both the new and old custom builders who rarely choose them as a platform to base a build on. For us at Cycle Source, we couldn’t imagine a more perfect platform to build a fun bike from, no wait…. These bikes can be bought for 2500 – 3500 dollars, have bulletproof Evo engines that are easy as hell to make more power from. With a wide range of parts to choose from and maybe with some modifications you could end up with a pretty trick bike on the salary of a low budget rocker! What we intend to do with this 1991 FXSTC is to take parts of it back in the day, update some of the others and make a bitchin Low Rider bike that Twisted Tea will be giving away this year.

We are going to start with installing Dirty Bird Concept’s “Dirty Tail” FLH Swingarm conversion. This will take away that trademark Softail rear swingarm and give us more of an old bike look with exposed shocks.

Here you can see we mocked up one of Dirty Bird’s Big Rear Fenders without swapping the swingarm. It’s OK, but the softail swingarm has to go.

The first step is to strip away all the stuff that’s in the way. The wheels, belt, belt guard, brake, splash guard etc.

Really the only thing you need to remove to drop the swingarm are the hidden shocks and the pivot shaft. Two bolts, one on each side of the swingarm. With that out of the way we can prep the new part.

OK, so here is where I have to fess up. Dirty Bird’s kit is for a 2001 up. Those bikes are a little more pricey still so we are going to try and retro fit his kit to this 1991. Sideshow Cycles gladly explained the how to before the part came in so we are pretty confident.

To start we press in the new bearings, but unlike the way you would for their normal application, we press them in from the inside of the swingarm. This will give us the correct spacing on the outside where the spacer between the swingarm and the frame has to go.

In this picture you can see that once we installed the pivot shaft with the new swingarm, there was an extra .21 space on the one side. Apparently the 2001 and up Softail is slightly narrower at this point.

No big deal, we stopped at Ace Hardware and picked up a hardened spacer and off to see Mr. Fish. Our lathe is broken so Ed offered to cut the spacer for us.

Here you can see the pivot bolt, the pivot shaft and the spacer cut to our length. Now, we didn’t feel it was necessary to have equal spacers on both side since the pivot shaft doesn’t need to be centered and the bolts have plenty of thread on each side to support the shaft.

Here we have our new spacer in place and the pivot bolts tightened. With a good fit, we can now move on to installing the shocks.

Dirty Bird provides these great top shock mounts in their kit as well. This is a well thought out part and all the components are solid.

To accommodate the mounting hardware for the new top shock mounts we have to drill out the front holes in the frame horns to 1/2 Inch.

With a little blue tape applied to keep us from scratching up the new chrome, we install the top shock mounts. It looks like too much at first, but this is to compensate for how far in the Softail frame horns dip in.

Before we move on to mounting the shocks, we should mention that Dirty Bird also supplies this great bracket for adapting the stock, or in our case PM brake. Since the Softail has an upward angled frame rail that holds the brake stay, the addition of this bracket means you don’t have to pitch the brake caliper you have already. Kudos on behalf of the budget minded!

With the shocks mounted here you can see that those top mounts will line them up perfectly to the lower mount locations.

We swapped the fender, strictly due to the fact that this one from Klock Werks is slightly narrower and slips in without any further alteration to the frame horns. I’m kinda rough with paint so this makes Mark more comfortable.

With the wheel on you can see how bitchin the rear of this bike is going to look now. That is an 18 inch rim to give it a little more meat under all that fender. We will be matching that rear wheel up with a 21 inch wheel up front that has a 3.5 inch rim width to carry that fat theme a little. But that’s a story for next month when we will be swapping the front end to be an old style nacelle with a set of FLH legs. This is able to be done with a nice little kit from JP Cycles that converts a Fat Boy or Heritage style front end to the Nacelle. The only thing we have to do is convert our wide glide to a Heritage style. That’s where we’ll pick up next month. Until then, you can get more info on the Dirtytail Kit from Dirty Bird Concepts at https:// fl-style-swing-arm-2001-to-2017/

3 thoughts on “Installing A Dirty Tail Kit

  1. Whaat? Two comments? This should be the most fun topic ever! I am a harley fan, and would jump on a deal for an old softail project if one came along, the original concept was all about cosmetics… The damn thing shouldn’t even exist, but the new crowd was demanding features like more gears and bigger engines, stuff that didn’t make sense for bikes that already had monstrous pistons and crazy torque. So, here we are looking at regular swingarm retro/ conversion kits – this rules!

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