HarleyTechTalk

My 1974 XLCH has a HD mag wheel twin disc front end. The bike cane with an extra pair of fork tubes. Whats the distance from tree to top seal stock? I have about 6"... [attach=0]  The GB500 fork boots I got appear they'll be a bit short

Gonna be tough, as your Dual Disk is Not Stock...and I assume either a Morris or Lester Wheel... but, I will measure a Stock 1975... [same front end]
Gimme a bit... it is actually snowing right Now!!!!

 There's a 19" Morris on front and a 16" Lester on the rear. Last owner claims the front forks/twin discs are off a late 70's Low Rider, but I see pics of late 70's Ironheads with the same setup. I anxiously await your findings.....

Dual Disk was a Stock Sportster thing 1978 and 1979... IDK about 1980..
about the same, give or take a year for the SuperGlide..
The measurement you desire is from 5.5 to 6 inches...depending on spring sag... on my stock examples..
I doubt that the Trees on a 1974 are from a SuperGlide... unless someone changed the Neck stem... which is what Willie G did when he adapted the XL front end to the Glide...the XL did Not get a 1" stem until? '79 or maybe '80
I'm too lazy to check this closer..

A quick skim of the parts manual reveals Sportsters and FX's use the same fork tubes, depending on year and model.

54-72 XL, 71-72 FX
HD 35mm
22-3/4"
HD 45953-71

73-74 XL, 73-77 FX-FXE
Kayaba 35mm
23-1/2"
HD 45977-73

75-83 XLH-XLCH-XLCR, 83 XLX, XLS, 76-83 FX-FXEF
Showa 35mm
23-1/4"
HD 45407-75

79-82 XLS, 77-83 FXS-FXB-FXSB-FXR-FXRS
Showa 35mm
25-1/4"
HD 45644-77

Springs are different based on model, as are fork lowers (sliders) based on brakes.

-JW

Quote from: JW113 on April 22, 2020, 11:08:37 AM
A quick skim of the parts manual reveals Sportsters and FX's use the same fork tubes, depending on year and model.

54-72 XL, 71-72 FX
HD 35mm
22-3/4"
HD 45953-71

73-74 XL, 73-77 FX-FXE
Kayaba 35mm
23-1/2"
HD 45977-73

75-83 XLH-XLCH-XLCR, 83 XLX, XLS, 76-83 FX-FXEF
Showa 35mm
23-1/4"
HD 45407-75

79-82 XLS, 77-83 FXS-FXB-FXSB-FXR-FXRS
Showa 35mm
25-1/4"
HD 45644-77

Springs are different based on model, as are fork lowers (sliders) based on brakes.

-JW

The reason the years denote different forks, is, in fact due to the different front brake...as well as length.. good on ya for the list. Add the brake used to the list and it is awesome... again, I'm lazy, and I hate doin this "Potty mouth" on my phone!!

Just to make clear, this is ONLY the fork tubes. Not the complete fork assemblies. But the question was about length of the tube, so hope this addresses the question.

-JW

Quote from: JW113 on April 22, 2020, 01:32:30 PM
Just to make clear, this is ONLY the fork tubes. Not the complete fork assemblies. But the question was about length of the tube, so hope this addresses the question.

-JW

Yea Gotcha... Hawg Rider has this info in a different format... In a Different place... well done also.
If you don't mind, one day I may combine your [great] info, with his!!!as a Downloadable... "tutorial"

This gets fugly

add these to the list
45955-71 low ground clearance 71-72 XLH

45953-68 high GC 68-70 XLH XLCH
45955-68 low GC 68 - 70  XLH

Although none of these were disc brake forks including the 45953-71 high GC 71-72 previously mentioned.

Also the Kayaba fork is the first aluminum lower and was the first year (mostly) single disc banana caliper and was not available in 2 lengths.
So excluding the Kayaba fork there are only 2 fork lengths for the disc brake forks (Showa).

The pie caliper began the era of the Showa forks, dual discs were Showa as well.



These might be short forks (Low GC) if they are fully extended, but I think they may be long forks with saggy springs (un-shimmed).
I have both long and short tube forks, My short ones measure 5" from the bottom of the tree to the rubber boot (fully extended) and those are measuring 6".....
Long tubes would measure near to 7" that way fully extended, and since those are over 5" I'd say they are long - 45644-77
I usually shim for 3/4 to 1" sag (with the rider) from fully extended.

They are Showa and from what I see here, the 25 1/4" variant.
So; I should measure the other tubes that were included in the deal.
I'm certain if the ones on my XLCH were 1.75" shorter, all would be fine.
Should look at replacement springs, though.
Super helpful resources here. 
Not gonna chop/bob or stroke this bike, just to refine what I have will be enough $$$

Any springs will "work" I use PVC pipe (to shim at the top) cut to length with a washer to keep the spring from eating at the plastic.
A longer spring is softer, and I prefer to not use progressive wound springs.
Because the travel is not long enough to give up the travel needed to overcome the soft part of a progressive spring.
Lengthening the fork tube does not change the travel.

Over on the XL forum I found a pic that may be a Kayaba 74 pie caliper leg with no axle cap?
I discovered that the XL parts book skips any 74 model without a banana caliper?
I always thought that when the supply of Kayaba forks was exhausted they switched to Showa/pie in 74.
But maybe not?
WTF?

But but but... in 1974 I have yet to see a Bannana... 1973 Yup... all of 'em I have seen... Kayaba's with a Cloverleaf/Pie slice? More than a few.. Slippery slope... Later, I will measure my 1974 PieSlice/Cloverleaf forks... I do Not have an early Banana  front on the Farm... except of Course Big Twin Baggers...

Had a bigger-than-me friend sit on the XLCH today, and the front sank nearly 2".
It did look more "level" but the stock springs are definitely sacked. Perhaps a "lowering kit" designed for my Showa forks would be an answer? Definitely need new springs.....and I have a pair of gaiters to install

I put gators on my forks because the bugs on my forks (from hauling ass) would make the seals leak.

The sag you are seeing is likely partly due to progressively wound springs and that they have not been shimmed correctly.

To fine tune your forks any spring will likely need shimming, as you saw the riders weight changes the amount of sag.

RaceTech sells non-progressively wound springs for your forks, these are my favorite.
They have springs for an early XL or a FXE, Call them and they will help you chose a spring that is right for you.


Don't go crazy with stiff spring rates for the street.
A famous racer said "any suspension will work, if you don't let it"!

Quote from: Burnout on April 24, 2020, 09:42:23 AM
Don't go crazy with stiff spring rates for the street.

Stiff suspension is thought by many to be a "performance improvement". Just the opposite is true. On a motorcycle, stiff suspension means the bike will jump over bumps and road imperfections, rather than soaking them up. When the tires lose contact with the pavement, especially in a turn, that is not an improvement.

-JW

I had RaceTech springs in the front of my '01 XL. They worked excellent.
I'll contact them and see what we can do...

I was talking with a walking HD encyclopedia this weekend, and he told me I was looking in the wrong parts book for info on the Kayaba forks.

Apparently they were used on Big Twins up to 77!
It was also recommended to avoid them because they are easy to ruin as the top of the leg is very thin around the seal and breaks easily.