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Although it doesn't say you can do it in the service manual on a 1986 FLHT, I changed fork oil in mine today by injecting the new oil into the drain hole with a syringe I found. I first removed the core from the schrader valve to relieve the air pressure in the forks, then pulled the drain plugs, then pumped the forks a few times to get as much old oil out of the damper piston as I could.
The syringe only holds 5 oz and the spec is 7.75 oz with a "wet" fork. So I put in 5, then put the plugs in. I exercised the forks about 10 times, pulled the plugs and drained it again. I got quite a bit of red dyed fluid on the re-drain, so I did that one more time before it drained clear. Then put in 5 oz, plugged the hole with my finger while my wife pulled in 3 more oz of oil in the syringe, then put the 3 oz in. In the process of refilling the syringe and getting the plug in I lost about a 1/4 oz so it's pretty close.
The is the biggest syringe I could find:
The shop manual says to remove the fork caps to change oil in the forks. But with the core removed from the schrader valve there is no back pressure as you inject the new oil, so it worked fine here.
The forks had ATF in them and it wasn't real dirty when it drained. I've always used SAE 10 power steering fluid or hydrostatic drive oil in the forks on every bike I've owned in the last 35 years, so that's what I put in this one. With the new oil and 10 psi of air pressure in the front we took the bike out for a two-up test ride and the front end feels great and the anti-dive even works properly again.
I did something similar last week on my Electra Glide, only I used a vacuum pump to draw the new fluid in from the top. Way easier than taking the fairing off to get to the fork caps.
I went with 20wt DelRay fluid, and liked you noticed an immediate and positive improvement.
The shop manual said to use Harley Type E fork oil, which I think is SAE 10. Most ATF is SAE 15 and for whatever reason the anti-dive did not work on the bike since we bought it. The selenoid clicks when you apply brake but there was no anti-dive action. After changing fluid, flushing the forks and getting the new fluid in there that anti-dive suddenly started working. It's only on the left fork but it makes a pretty dramatic difference in front end dive when it's actually working vs when it's not.
The big Electra Glide will never be a racing bike, but with the new oil it feels much more positive and compliant in the corners and under braking. And much better ride on bumps in straight up riding. The owner's manual says to change fork oil every 10K miles and that's something I admittedly ignore and only do it once a year. We put on 22,000 miles last summer and never changed it. But the results of changing it is a reminder that changing it at 10K is probably a good idea. If you go far enough to get oil that looks like aluminum paint when you drain it your poor bushings, slider and damper have already bit the dust. So getting clean oil out when you drain it is a good thing :-)
Both sides are controlled by the air system via the valve body and crossover tube from one side to the other.
For the air suspension, yes. But the anti-dive valve is only on the left fork tube. It comes on under braking and restricts oil flow only in that fork tube so it doesn't compress as easily. I'm thinking the little piston was stuck before I changed oil. Getting new oil in there and working it with the ignition on so the selenoid tried to pull the anti-dive valve in when I applied front brake to work the forks, freed it up so it now it works.
Edit: I just re-read the FSM and you may be right on that. It appears the anti-dive valve shuts off air pressure to the reservoir (crash bar), trapping the air in the fork tubes. This causes the air to compress to higher pressure under braking so it becomes stiffer and doesn't compress as easily.
Mine had some oil in the crash bar when I took the schrader valve out. Whatever the situation was with it, it works now and I like it.
Last edited by Harley-Davidson; May 10, 2016 at 09:06 AM.
I had wrongly assumed that valve meters oil like it does on metric bike anti-dive forks. One thing the Harley system has going for it is that it is simple. And it works really well. Can't really complain about the handling and ride for a full dresser.
One thing the Harley system has going for it is that it is simple.
That it is.
And it works really well.
I wouldn't go quite that far, but it does work. Like you implied, there is a limit to how much handling you're ever going to get out of one of these beasts. After tuning up my forks and zipping a bit of air into the bars, I'm fairly pleased with the result.
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Changing Fork Oil
