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Fork Oil

68K views 51 replies 22 participants last post by  Kainam 
#1 ·
Fork oils are as follows:

Harley Type E is 5 wt
Harley Type B is 10 wt
Screaming Eagle is 15 wt
Screaming Eagle Heavy (racing) is 20 wt

By adding the spacers in the fork tubes, you increased preload, causing less dive.

Adding thicker oil slows compression damping, however, if it gets cold in your area, 20wt can be a little too heavy and start making a "knocking" noise in the front, on fast movement, or while going over bumps. As can 15wt....

Your results will vary.
 
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#2 ·
Mobil 1 Dexron ATF is equivalent to a 7.5w fork oil.

Shovelhead service manuals used to call for ATF in the forks.
 
#10 ·
I have been running off the shelf Lucas hydraulic fluid this year. Put it in because it's very inexpensive and has good seal conditioner and anti-foaming additives. Cost me about $18 for a gallon jug of the stuff and I can use it in my floor jacks too. My gut feeling was it would be too slow. But, I've been pleasantly surprised, on the slower end of the damping scale but it performs well. I've ridden in temps down to the mid 50's and no issues with knocking.
 
#22 ·
Cold winter weather = stuck in the house. Found my way back into this thread. Ran the Lucas hydraulic fluid all summer and liked the way the bike rode and handled. Fork is a little stiff when the temp drops below 50 but I never experienced any funny noises or poor performance. I got into the viscosity thing back when I was doing the project. I didn't save any of the data reviewed but basically concluded that the Lucas is around the high range of shock oil viscosity scale (10-12) and that shock fluid has it's own scale so they can charge you more by adding confusion. In the end it's light oil with seal conditioner and anti-foaming additives and even better it's cheap, less than $20 got me a gallon jug, have two bikes and two jacks so its probably close to a lifetime supply lol!
 
#12 ·
So in looking at the CLymer manual I have for my bike it recommends a Type E oil in the forks....

If I ran a heavier oil would that just stiffen the suspension more?

I know most stock bikes are set up generally for a 185lb rider, and i'm 260 without gear so i'm just trying to get a stiffer ride, some times when I hit bumps me alone will bottom out the rear suspension.
 
#13 ·
Fork oils are as follows:

Harley Type E is 5 wt
Harley Type B is 10 wt
Screaming Eagle is 15 wt
Screaming Eagle Heavy (racing) is 20 wt

By adding the spacers in the fork tubes, you increased preload, causing less dive.

Adding thicker oil slows compression damping, however, if it gets cold in your area, 20wt can be a little too heavy and start making a "knocking" noise in the front, on fast movement, or while going over bumps. As can 15wt....

Your results will vary.
....and trash the Clymers.
 
#16 ·
Keep in mind for touring bikes..... 2005, left fork leg is a Cartridge. Both cartridge after 2006.
 
#18 ·
I recently did a fork oil change and tried to find the viscosity of the different ATF designations. I got so confused, I just bought Type F and put it in. My forks ('07 E.Glide) are just a tad softer now than with the factory oil. Dives more on braking, but sucks up the chatter bumps better.
 
#19 ·
This is one of those items that to me is easier to just get the oil from HD and pay the few cents more than at your local Wally World or Auto Parts place and then at least you know it is the stuff you're supposed to be using.
 
#24 ·
Cool, I grew up here. It feels small-townish for a suburb of Cleveland and I ended up coming back after school and as a bonus I ended up just 7 miles from work. Great in the winter, kinda sucks in the summer cuz the bike is just getting warmed up...
 
#26 ·
Fork oils are as follows:

Harley Type E is 5 wt
Harley Type B is 10 wt
Screaming Eagle is 15 wt
Screaming Eagle Heavy (racing) is 20 wt

By adding the spacers in the fork tubes, you increased preload, causing less dive.

Adding thicker oil slows compression damping, however, if it gets cold in your area, 20wt can be a little too heavy and start making a "knocking" noise in the front, on fast movement, or while going over bumps. As can 15wt....

Your results will vary.
Dave, would you care to elaborate and, would this spacer trick apply to my '14 FLHX ?
 
#29 ·
You have a mixed system on your 14 FLHX.

Right side is traditional damper system, in which the spacer would work to increase preload, and thicker oil to increase damping.


BUT left side on your bike is a cartridge system that none of the above methods would work.
 
#27 ·
Dave has taken a bit of a hiatus from the Board.
Basically what you are doing is shortening\compressing the springs. Even more then just the weight\preload of the weight of the bike.
This will cause them to be a bit stiffer while still keeping the original ride height.
Unless of course you have gone to a lowering kit.
By being stiffer you will have decreased nose dive when braking.

Think that is about right. There are some good Wrenches that may correct\confirm\elaborate as needed.
 
#32 ·
Motorcycles can use two different dampening (or 1 side only) systems because the axle connects the two forks, effectively making them a single system. Plus there is only 1 wheel, turns have not effect. Harley is not the only one that does this.
 
#34 ·
Now I've gotten all twisted up in model differences. I THINK HD discontinued the different side dampening forks in 2005. 2006 up models are same both sides. I'll try and look it up later.

As for the WHY use two different systems, I guess one costs more, so they save money. Gotta remember, pennies saved on the assembly line = better bottom line on the quarterly P&L statements. And I think, the fork tube assemblies come pre-assembled from Showa factory in Japan.
 
#35 ·
Does Fork Oil replaced and she bottom out!

I took my 2012 flhtk in for its 25K service and the front end now bottoms out on minor bumps in the road. (Not happy) the bike feels loose to me. Took it back to service and the tech say she rides fine to him. They did adjust something in the head tub? not sure if I saying that right and gave it back to me. The service guy said he could change out the fork oil to screaming eagle fork oil if the ride is still not to my likening. Not sure which way to go.
 
#36 ·
They might have tried adjusting the fork neck bearings and set them to loose, that would cause a clunk in the front end.
The "fall away" test would confirm if the neck bearings are adjusted correctly.
 
#37 ·
Changed the fork oil over the winter, used the Screamin Eagle 15. Brake dive was cut way back, front feels much tighter. Haven't taken it on a long run yet. So far so good.
 
#43 ·
Nothing. HD's service interval for 2005-up is 50K.

Synthetic would just separate you from your money.

My 2005 has mixed internals. Cartridge one side, regular internals on the other.
 
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