HarleyMotorcyclePartsFat Bob (FXDF) Rear Shocks: Tyre Clearance Comes First
Those fat 16-inch tyres leave less room than they seem to. Check the gap and the exhaust side before you buy or fit.
A fat tyre under a fender looks like a tough, simple arrangement. In practice it is the first thing on an FXDF to run short of room. When a new shock changes length, the 16-inch rubber moves closer to or further from the fender, and a shorter unit at full compression can leave very little gap. Most buyers look at ride quality alone. On this bike, measure clearance and read the exhaust side before anything else.
Tools
- Steel rule
- Masking tape
- Rags to protect the exhaust
- SAE tools
- Torque wrench
- Jack or lift that bears on the frame
- Workshop manual
A clearance figure to work from
Get the bike upright and unloaded on flat ground. With a steel rule, measure the smallest gap between the top of the tyre and the fender above it, and record that. Then look along the sides, as a wide tyre may come nearer at its shoulders than on the crown.
Now take the same gap again with a helper sitting on it. The difference is a rough picture of how much movement has been used just by sitting down.
Because each shock sits ahead of the axle, the wheel generally travels further than the shock shaft does. So a stated shock travel figure understates the distance the tyre moves. Allow for this if you are thinking about a different length, and ask the shock maker whether it has been checked on the FXDF.
Thinking about the 2-1-2 side
The exhaust layout on this model is the practical obstruction. Walk around it and try a socket on the fasteners with the bike cold, ideally before it goes on the stand. You will soon see whether an extension or a box spanner is needed.
Never start this job on a warm bike. Protect any chrome or black finish near the lower mount with a thick rag. A socket slipping off under force will mark it instantly.
If a pipe truly blocks a fastener, the manual covers the correct removal order. Do not bend or prise anything out of your way.
Keep a note of any bracket or clamp you do loosen, with a photo of how it sat. Exhaust hardware that goes back slightly crooked can rattle or touch the new shock, and that is a sound people wrongly pin on the suspension.
Supporting that weight
Take the load on the frame, not on the pipes. A jack pad under the rear of the exhaust is one of the classic ways to dent one. Lift until the fat rear wheel just unloads, and then stop.
Fit a board or a block under the tyre, so the swingarm has something to rest on and does not bear on its mounts. Secure the frame to the lift. A wide tyre on a narrow block needs centring properly.
Removal, starting with the easier flank
Do the open side first to learn the fastener sizes and stack with nothing in your way. Tape a small tag on the old shock saying which side it came from and which end is up.
Slacken the top fixing, then the bottom. Save the washers in order, and keep the other shock tight, since that is your swingarm's only location during this step.
Slide the old unit free. It may need a slight twist, particularly when its bushing has aged and gripped the stud.
Mount check
Examine what the shock left behind. Bushings harden and split; studs develop a worn band where the eye has been working. Either fault can pass a clunk along to your new parts and should be dealt with before refitting.
Confirm the stud sits solid in the frame. A wipe with a solvent-damp rag will often reveal a small crack or fretting mark that grime had been hiding.
Putting it together
Bring the replacement up to the mounts and use the block below the tyre to tune height. The eye should slide on square. Refit the hardware in the same sequence and tighten by hand.
Use a torque wrench for the final tightening. The specification is listed in the manual for your year; look it up rather than guessing. Take your time on the exhaust side, where a wrench at an awkward angle can give a false feel.
Then deal with the second side in exactly the same way, and match any preload settings.
Verifying the gap
Back on the ground, retake your rule measurements, with and without a helper aboard. Compare them with your notes. If the new number has shrunk a lot, get expert advice before you ride.
Next, look at the tyre with the bike at rest on its stand, then ride a short route with some honest bumps. Afterwards, check the fender's underside for any fresh scuff or rubber mark. That mark is the tyre telling you the real number.
Finally, recheck each fastener, and check that nothing on the exhaust side has been knocked or scratched.
Mistakes that cost money
- Choosing a length without measuring tyre-to-fender clearance.
- Assuming wheel travel equals shock travel.
- Jacking under the exhaust.
- Starting the job with hot pipes.
- Ignoring a rub mark inside the fender after the first ride.
When to stop
A fresh rub mark on the fender underside means the tyre has reached metal. Do not keep riding it. Under load that contact can stop the wheel or damage the tyre.
Parts for this job
Check fitment for your own model and year before ordering — add your bike and we will flag what fits.
Other Harley how-to guides
This guide covers procedure and judgement. Torque figures, fluid capacities, gaps and tension settings are specific to your model and year and must come from the factory service manual for your motorcycle — we deliberately do not print numbers we cannot stand behind for your bike. Independent aftermarket retailer, not affiliated with Harley-Davidson, Inc.