Check the REFerence Section for additional Suspension information:
Suspension Tools

* . . . 2014 XL1200T Front Fork Testing w/ Spring Rate Charts

* . . . 1994 XLH Front Forks Disassembled - Measurements w/Pictures

* . . . 1200S Fork Rebuild & Hyperpro Spring Fitment

* . . . 1200S Suspension: Settings

* . . . Future Subject

* . . . Future Subject

The front forks on most Sportster models consists of two tubes - A slider tube that is mounted in the triple-trees and a lower leg tube into which the slider tube compresses. Each slider/leg assembly has an internal compression spring and damper tube. The spring supports the weight of the rider & bike, collapsing or expanding to cushion the ride over bumps and cavities in the road surface. The damper tube is submerged in oil and uses the passage of oil between internal chambers to help control the speed with which the slider/leg assembly compresses together & expands apart as it cushions the ride. Because the damper tube is attached to the lower leg, the length of the damper tube determines the amount of 'travel' the slider tube has within the lower leg.

In addition to the internal physical spring, there is an 'air spring' effect caused by the amount of air above the oil level in the fork assembly.

Functionally, there must be enough fork oil to fully submerge (engulf) the damper tube during its entire operational movement. The MoCo specified oil amount still leaves an air pocket above the level of the oil in the fork.

The air captured between the top of the oil level and the fork caps (which are sealed) creates an 'air spring' by which the compression of the air during fork compression helps the physical spring prevent total collapse of the fork, while also assisting the spring in expanding the fork after a compression event. The size of the air pocket, measured by determining the exact distance the top of the oil is from the top of the slider tube, can be varied (by adding or reducing oil) to produce a stronger or weaker 'air spring' effect (but the adjusted oil level must still allow the damper tube to be fully submerged during its entire operational movement).

Here's an example of the parts for that design (1994 Sportster XLH): ¹⁾

Here's a comparison between a couple damper tube sets. Notice they are of different lengths and that the holes at the bottom are different sizes. The actual length & size of holes varies by the model in which it is intended to be used.

The length of the tube partly detemines the overall slide movement range. The size of the holes at the bottom of the tube determines the rate of exchange of the oil between internal chambers when the fork is compressed. This helps control how quickly the forks compress.

The set of damper tubes on the left includes the 'top out' springs which help cushion the end of travel when the forks expand. All models use the same top out springs (as stock).

Racetech has a fairly detailed explanation of Damper Rod Forks, along with their promotion of cartridge emulators, at this site: https://racetech.com/page/title/Emulators-How%20They%20Work

TIPS

The 39mm Fork Caps (which are 6-pointed) need a 1-3/8“(1.375”) 6-point socket or Cap Wrench. A usable equivalent is a 35mm(1.378“) size. It's a good idea to wrap masking tape, electrical tape or duct tape (depending on the thickness of the tape) around the chrome cap to protect if from marks. ²⁾

Use a 6-point socket, rather than a 12-point version, to lessen the chance of rounding the points on the cap. This is also why an adjustable wrench should be avoided.

Loosen (not remove) the Damper Bolts (6mm Allen Key) while the forks are still on the bike so the spring tension can help hold the Damper Tube (internal) from rotating while loosening the bolt.

For reassembly, prepare the fork cap by aligning it with the slider tube (no springs installed) and mark the exact point (on both the cap and the slider) where the threads begin to engage - This is extremely helpful in getting the cap back on while compressing the spring.

Use a 1-1/2” PVC coupling for the fork seal driver (coupling center spline removed).

45790-80 - Stock JIS-head Drain Screw with Washer (Requires 1 for each fork)

• (Starting in 2008, some models do not have fork oil drain screws)
• (Use a JIS screwdriver for JIS screws. JIS screws look like Philips screws with a dot in the center of the head, but the JIS version is a wider blade with different spline angles. Using a Philips screwdriver on a JIS screw will often round out the screw head. However, using a JIS screwdriver on a Philips-head screw may work just fine, since the driver splines fit snugly on the upper, heavier part of the screw head.)

45815-03 - Chrome Fork Slider Drain Screw Kit ³⁾
Screw size is M4 (0.7mm) × 6mm - Includes a pair of chrome allen head drain screws and washers - Uses 2.5mm allen key.
(Try a 3mm allen key first, the chroming takes up some space in the hex slot)

You can also upgrade to socket head (Allen head) bolts to help prevent stripping out heads.
These are stainless steel bought from a hardware store. Size M4 (0.7mm) × 8mm.

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Abbreviations:

• Std = 883 Standard Model & 1200 Standard Model
  
• Dlx = 883 Deluxe Model
  
• Hug = 883 Hugger Model
  
• Ctm = 883 Custom Model & 1200 Custom Model
  

Upper Slider Tube, Damper Tube & Spring (same on both sides)

Slider Lower Legs (Except 1200S)

Spring Notes/Rates:
45372-92 - 21.5” - 47coils - Rate reported as 40#/in ²¹⁾ 45376-97 - 20.5“_DR - These are dual-rate springs while most of the other fork springs are single-rate

See also Setting up the 1200S Suspension

Slider Lower Legs

• 1200S sliders don't have drain plugs. So, here is one way of doing so. ³⁰⁾
• Basically, once you have the forks out of the bike, remove the large top nut (loosen it slightly while you have the forks clamped in the lower triple tree, (as shown here Part 4 Dismantle the Forks ) while holding the slider. There is no spring pressure on this nut, so it's easy. ³¹⁾
• The slider will drop away, but don't let it drop more than a couple of inches or you'll have oil pouring out and not know how much has come out. ³²⁾
• Carefully tip the fork upside-down and pour the oil into a clear measuring container (a wide funnel will help you to not lose any). ³³⁾
• Bring the fork upright and pull the slider to the very top again, pump the fork a few times to empty the damper tube, then turn it upside-down again and pour more oil into your measuring container. Repeat this a couple more times to get as much of the old oil out as possible. ³⁴⁾
• Check how much oil came out of the fork, make a note of it, then pour the old oil into a waste container. ³⁵⁾
• Measure the same quantity of fresh oil into the measuring container, then, with the slider still close to the top of its stroke, carefully pour the oil into it. You're pouring the oil between the coils of the spring, so you need to go slowly and keep the fork vertical to avoid losing any. If you can get your hands on a funnel and fit a narrow flexible hose to the end of it, it may make things easier. ³⁶⁾
• When all the fresh oil is in, thread the slider onto the top nut again; clamp the fork into the bottom triple tree only to hold it steady while you fully tighten the top nut; then push the fork all the way to the top again and clamp it in place. ³⁷⁾
• Repeat on the other fork. ³⁸⁾

• Be careful, with the Low bikes, taking out the shock caps. There is about 2 1/2 ” of spring preload so the cap wants to come out in a hurry. I am about 200 lbs and fairly strong and it was about all I could do to reinstall the caps with a 1 3/8 socket on a 6“ extension on a ratchet. ³⁹⁾

(Same parts used on both left & right sides)

(Measurements for this section contributed by XLForum member, including this thread: https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-suspension-frame-forks-handlebars-fuel-tank-oil-tank-fenders/191729-hd-part-numbers?t=2045589)

These forks use a combination of Left-side Cartridge & Right-side Damper Tube

Here's a thread by 'Tomcatt' of the XLForum regarding changing to aftermarket springs & changing the oil viscosity/level in these mixed-tech forks:
https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-suspension-frame-forks-handlebars-fuel-tank-oil-tank-fenders/196520-2016-one-cartridge-forks?t=2073068

Inverted Forks use an upper slide tube that is the larger, outer tube while the lower, inner slider tube is used to attach the wheel. This is upside-down from the traditional damper tube design.

Reference Additional Information on the 2004+ models in these XLForum Threads:
https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-suspension-frame-forks-handlebars-fuel-tank-oil-tank-fenders/113966-ricor-mods-on-nightster/page2#post2432666
https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-suspension-frame-forks-handlebars-fuel-tank-oil-tank-fenders/170361-installing-works-performance-fork-springs-in-a-2014-xl1200-c?t=1827354
https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-suspension-frame-forks-handlebars-fuel-tank-oil-tank-fenders/113966-ricor-mods-on-nightster?t=1085901
https://www.xlforum.net/forum/sportster-motorcycle-forum/sportster-motorcycle-suspension-frame-forks-handlebars-fuel-tank-oil-tank-fenders/183137-wrong-damper-tubes?t=1971682

The Fork Service Kit is a collection of the parts recommended to be replaced for refresh maintenance. It includes all the parts that function between the Upper Slide Tube and the Lower Slide Tube plus new damper/cartridge mounting screws & Fork Cap Seals (O-ring). Each kit will refresh ONE FORK TUBE.

For the models that use the same Fork Service Kit, one might expect the upper & lower slide tubes to be functionally compatible across all years (that's an assumption - there might be something that IS incompatible - but unknown).