Why do my forks knock over bumps?

[Guest]

So when I hit descent bumps my forks knock. Why is this? I rebuild them to spec with new progressive springs. Any Ideas!?! Thanks.

[Steve]

Did you set your "sag" properly?

How much of what weight oil did you put in?

Did you check the condition of the bushings while the forks were apart?
(They might have a bit of wear on them, letting them move around.)

.

[SVSooke]

My first thought was loose steering head bearings.

[Steve]

Also a good possibility.

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[thkbaron]

I will check all those things. I may not have gotten all the air out when I rebuilt them too. That's a possibility. I'll check them out this winter after riding season. I should probably replace the stem bearings anyways.

[Steve]

There is no need to "get all the air out", as in applying a vacuum to the forks. You simply don't need to add any additional air when using proper springs. However, you DO need to make sure they are preloaded enough to limit your "sag" to 20-25% of available travel. In the case of most GS forks, that will be about 1 inch of sag.

If the noise happens to be loose steering bearings, your "riding season" might be shorter than you think. Besides being a source of noise, loose steering bearings can do some really strange things to the handling of a bike. Hope you don't crash.

.

[chuck hahn]

Sure its the forks and not something else rattling and your thinking you hear the forks?? Take some tape and put it across the back of the gauges and anything else that may be subject to rattling and take it for a ride on a good bumpy street and see what it sounds like then.

Because we are moving and wind plays a role in things, we often hear something and its not from where we "think" we are hearing it from.

[mrbill5491]

I read somewhere, progressive front springs can knock due to the "progressivness of the spring" Though I would heed some of the other advice here and look at some other things as well, steering head bearings, wheel bearings (had a bad on one my bike once that would knock when I hit a bump), the internal slider bushings in the front. Also check the brake mounts and make sure one of them hasn't come loose. Just FYI, alot of us on this forum use straight rate fork springs from Sonicsprings.com. Check them out.

[thkbaron]

Well I'll revive this one. Been a while but I just re did my forks. I lengthened the spacer on top of the spring a bit and the problem has mainly gone away.....if I hit some really nasty bumps it will still knock but it's better than it was.

[gs45082]

I had a momentary panic when I noticed a severe clunk when coming to a hard stop. Turned out it was my speedo rocking in the mount, rubbers were AWOL.

Well I'll revive this one. Been a while but I just re did my forks. I lengthened the spacer on top of the spring a bit and the problem has mainly gone away.....if I hit some really nasty bumps it will still knock but it's better than it was.

[JamesWhut?]

If its coming while you're under braking, you are probably bottoming out the forks hard, and then the sound is either just the spring and slider "crashing" or as mentioned something else in the front end or somewhere moving and making the noise.

[thkbaron]

So I rebuild my forks today. New 15 w fork oil and I found out the put the progressive springs upside down and may have had the incorrect amount of oil in so ill let you know when I get to drive it again.

[gsrick]

Just saw this thread and had to go back and look at the posting dates. You sure take your time fixing things. lol

[thkbaron]

It was an annoyance not a necessity. The seals finally started leaking so I took the opportunity to do the rest and investigate a bit.

[GSXR7ED]

Interesting thread. Good pointers too, as I have yet to rebuild my forks. (Doh!)

Yes, Rick -- some of us take a long time to complete tasks. Lol


Ed