What would make the forks rattle at about 3000 rpm and when striking sharp bumps?

Harley put new fork oil in them, and I did again when I replaced the damper rings. The brake calipers are not makng noise. The steering bearings are neither too tight nor too loose and there is no play there.

Kinda sounds like the bound up springs vibrating against the fork tubes. Hitting the front brake has no effect on the sound, and the rattle is still there when coastng over a series of bumps at idle rpm.

Clues anyone?

 

Did you also check the fender mounts, I heard that sometimes the fender bolts can back out, can you here it at idle with the bike just parked. Those springs in the fork are compressed, I can't imagine they would be able to rattle inside the tube.

 

Fender bolts are very tight.

I notice that the rattle comes in if I am tight up against the RPM point, then go downhill or move my weight back as I do going downhill. Move my weight up front and the noise goes away.

There is also a secondary spring in the slider under the dampers. I have heard that the springs can make noise, and am sure that out there somewhere someone has addressed this problem correctly (of course I could spend a fortune and replace the front end). I understand that there was at least one case where the owner wrapped his springs with cloth. I would not take that route!

The previous owner weighed about 80 pounds more than me, so I am wondering if the springs may have set to a heavier rider over time.

 

BLR, jack up the front end so forks are fully extended and remove the long fork springs. There should be some resistance when you remove the fork caps. If no resistance you could have a broken spring or springs that are fatigued due to age. Make sure the springs are of the same length. Another option at this time would be to install a set of progressively wound springs. They are not that expensive and will give you better handling. Post back when you find the problem....................BG

 

I already have removed and checked the springs. There is NO resistance when pulling them out, yet they are very strong. They stick out of the forks three inches at least with the forks fully extended. It is a real battle to get the cap back on.

The top springs are not broken and are the same length. I think I must dissassemble the forks to get at the lower springs. That would be a dealership job for me, and very expensive.

I pushed the damper up from the bottom with a brass rod to replace the damper rings. Left fork damper came out no problem and had worn rings. Right fork damper was tight and kept getting stuck, so I fished it out with a long wooden dowel - rings ok. This took me all day because I have to work outside and it rains alot here in New Orleans (Yes I do cover it to keep water out of the forks.)

Spending more time or money to take the forks apart without some experienced person relating a successful fix to this problem could be a serious waste. If I must replace the questionable Showa metric (Japanese?) forks, then I do not want to waste any more time or money on them.

This morning when I rode in, I hit a bump pretty hard and the sliders hit the stops. So maybe non-linear springs would help? Remember the fork oil is fine. Am using Harley Type 'E', recommended by Showa.

Thanks for the suggestions !

 

BLR sorry I confused you a bit . The resistance I was refering to is when you took the caps off and the springs kind of jump out a bit, but you already said that happened and that its difficult putting the caps back on so I will assume the springs are both good from what you described. Since the forks are bottoming out it now sounds like the dampers themselves are not doing their job. When you first purchased the bike did you notice these problems you are having or only after you had the dampers out? Did you have oil inside the dampers when you reinstalled them or is there a possability you have air trapped in the dampers? These are just suggestions, maybe someone else has had this specific problem, anyone??.....................BG

 

Noise was there from day one when I bought the bike. I asked about it then and was told it was the brake caliper. Since the caliper was rattling at that time, I didn't realize the forks were also until I re-bult and fixed the caliper. The caliper noise (pad noise actually) dissapeared when the brake was applied, and I wasn't at or above 3,000 RPM when I first checked that. Fixing the caliper was easy, and a new one is not real expensive. New forks are a different story. When I started looking at the forks because of this clacking, I discoverd they were almost dry. My first step was to replace the fork oil. I did not pull the dampers until that did not work.

There cannot be air trapped in the damper for long because the top is open and there are several large holes in the bottom of the stem. Oil flow through the damper is what gives velocity damping. Of course this is an entirely crude and outmoded way of doing this job. Sportster forks have been improved since 91. Haven't they?? My many various metric bikes did not have this clacking problem, although I do remember a similar noise when I had my 67 Ironhead. I love my Sportster, but there seem to be a couple of design aspects that are really poor.

Here is another kicker. Once the forks start clacking, then the clacking comes more often and easier. Until I have stopped at a stop light, not hit any bumps in a while and stay out of the bad RPM range. This means that air is mixing with the oil and promoting the problem. The air settles out with reduced motion, with a rate related to the weight of the fork oil. There is air at the top of the forks, always about four inches uncompressed - to act as a final buffer. If you remove the air by filling the forks completely with oil and then if you hit the stops, your forks will rupture big time. Horrible mess then. So how do you keep air from polluting the oil? You can't!

What a strange design. Hopefully someone can show me a reasonable way to get rid of the clacking anyway.