Help with leaking fork seals
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Tourer
Joined: Aug 2014
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From: Frederick, Maryland
Help with leaking fork seals
So I have a 12 FLHTCU. Put a 21" fat spoke front wheel on and lowered the front with the Harley lowering spring kit. Since lowering the bike about 1 year ago, I have had to replace the fork seals 2 times and replaced the lowers once. First started off with a new set of seals and checked with the local dealership to make sure we were putting the seals in the right way and the correct amount of fluid, they confirmed we were doing it right on both sides. After they started leaking again, asked the dealership for some help and they said to check and make sure the inside of the lowers don't have any burs and to try smoothing them with a dremal tool. Did this and put new seals in and they again started to leak. I decided to just go ahead and get new lowers. I got a set of factory take offs and went thru the whole deal of putting it all back together again. So now, up to this point I am at 3 sets of seals and a new set of lowers. Took the bike out the other day and noticed oil all over the front fender, front of the tank and front head again. Talked to a buddy at a local bike shop and he told me that when you lower these bikes and start replacing the seals, they don't hold up very long. Has anyone else heard or had this happen to them? Any ideas on what to do?
Last edited by josh2002-ws6; May 30, 2016 at 10:01 PM.
Seasoned HDF Member
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From: SW Ohio
The "correct" amount of oil is measured from the top of the fork tube and not a liquid volume measurement. I may not be telling you anything you don't already know but I would put less than the factory service manual recommends for standard height (non lowered) suspension. Oil level is the first place I'd look. Keep in mind that when the measurement number in MM is lower, the fork oil volume is HIGHER. IE a fork with a measurement of 125mm (from the top) will have more oil in it than one with a 140mm measurement (from the top).
That said, I'd only use HD OEM fork seals. James Gasket fork seals have gone down in quality and leak. Changing fork seals on a touring bike isn't that big a job but it is frustrating to do it twice because of a poor oil seal.
That said, I'd only use HD OEM fork seals. James Gasket fork seals have gone down in quality and leak. Changing fork seals on a touring bike isn't that big a job but it is frustrating to do it twice because of a poor oil seal.
Grand HDF Member
Joined: Dec 2007
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From: Bay Area
Have you checked the upper tubes for burrs? Maybe theres a sharp edge when you install the seal over the tubes and its getting nicked? You should go over them with like 600 grit emery cloth. You may possibly have a bent or distorted upper tube???
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Tourer
Joined: Aug 2014
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From: Frederick, Maryland
The amount of fork oil is the first thing we looked at. I know you only fill it to the top of the tube. When I said that, I meant that because it is lowered the volume should go down but after speaking with multiple different Harley shops and other aftermarket shops, the volume doesn't change with the kit I used from Harley. I also only get the seals from Harley.
We checked the tube uppers also to make sure they didn't have any burs. Ran a cotton cloth over them and didn't catch on anything. Also nothing that can be seen. Did that on both lowers and nothing.
We checked the tube uppers also to make sure they didn't have any burs. Ran a cotton cloth over them and didn't catch on anything. Also nothing that can be seen. Did that on both lowers and nothing.
Grand HDF Member
Joined: Dec 2007
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From: Bay Area
Its easy to dislodge the wiper spring inside the seal if not installed correctly, just an idea. Maybe try rolling the upper tube on a piece of glass (glass is perfectly flat). I know you did say you have them installed in the right direction, but as an FYI way to check it is to spray wd 40 or fork oil on the tube and slide the seal over it. One direction will scrape the oil off (correct direction), the other will skim over it and pass oil (wrong direction).
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Tourer
Joined: Aug 2014
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From: Frederick, Maryland
That I don't know. I bought it used and didn't think to ask the guy. Why do you ask?
The only reason I added that was because I had heard that if you don't lower the front end, you can have a wobble in the front with the taller wheel.
The only reason I added that was because I had heard that if you don't lower the front end, you can have a wobble in the front with the taller wheel.
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Fork leaks come from several different things, you might be chasing a bit of a red herring at this point.
Yes, burrs and such damage the seal lip and cause it to leak. So too will a rock ding, a rust pit, the edge of a scrape. These can all damage the seal lip, and not snag a cloth rag. Btw, a silk scarf will find more things than a cotton cloth will.
Damage to the fork tube itself can result in the fork tube leaking oil, under the seal, without any seal damage. A polished rust pit is divot, and will hold oil. A smoothed scratch is an oil passage on the metal tube under the fork seal.
Crud and dirt build-up can also cause an otherwise perfectly good seal to leak, because it's being held off the metal fork tube. This is a very common problem with metric bikes and their exposed fork tubes. Less a problem with Harleys and their cow bells.
Yes, burrs and such damage the seal lip and cause it to leak. So too will a rock ding, a rust pit, the edge of a scrape. These can all damage the seal lip, and not snag a cloth rag. Btw, a silk scarf will find more things than a cotton cloth will.
Damage to the fork tube itself can result in the fork tube leaking oil, under the seal, without any seal damage. A polished rust pit is divot, and will hold oil. A smoothed scratch is an oil passage on the metal tube under the fork seal.
Crud and dirt build-up can also cause an otherwise perfectly good seal to leak, because it's being held off the metal fork tube. This is a very common problem with metric bikes and their exposed fork tubes. Less a problem with Harleys and their cow bells.
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Tourer
Joined: Aug 2014
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From: Frederick, Maryland
I agree with you and went to the dealership today and ordered a new set of fork tubes. When we installed the lowering springs, the right side spring shot out and hit my buddy in the face. I'm thinking maybe the spring bounced back and knicked the tube. The new tunes will be in middle of next week. I'll know soon enough. Thank you to everyone and I hope I can report back that it's been fixed.