Knocking sound on bumps

[Skropi]

Hey guys. I have a little problem that needs your troubleshooting super-abilities please 

When I ride my beloved bike ,when I hit bumps on the road, and I mean slight, veeeeeery slight bumps, they dont need to be potholes, there is a knocking sound coming from the front and I cant, for the life of me, pin it down.
That sound also appears when I brake suddenly and forcefully. I tried it with the engine turned off just to check it out. I tried holding the plastics when riding on some bumps to no avail.
I checked for play in the head/steering bearings, by pushing the forks left and right, and I didnt notice any clicking/play, and the handlebars do turn smoothly...
I tightened everything that tightens around the forks but that didnt help either... Oh, the caliper appears to be tightened too, but it also happens when I am not braking, so I dont think it could be it.
By the way I changed the oil in the forks with a heavier one, well, my mechanic did anyway, but the problem was apparent even before.
Any idea what the heck could be the culprit?

[jeZZa]

Hav you made sure that your tank is secure? And does it have the rubber bit around the edge of it? Also check your rear shock and multi link, had a similar problem with mine and it turned out to be the bottem multilink bolt had come loose
Goodluck

[Skropi]

I have no idea if the tank has the rubber thingy, but I "think" it doesnt. I will check it out but I am sure the noise comes from the front and not from the tank (could be wrong though). Will check multilink too, but I do wonder if that would be responsible for the above reason 

ps. How does the multilink look like? 

[sledge]

Have a look underneath and make sure the little rubber cushion the center stand sits up against is still there.

[Skropi]

The rubber thing for the centerstand is in place. I did put some tape to stiffen it out though. Tank is secure and tight, but it has the rubber lining only on the front, it doesnt touch anywhere on the frame though. What I noticed just now is that the knock comes from the shocks most probably. One knock when they press in, and another when they return  Maybe its normal and I am just being anal about it?
I will run some tests after I feed my kid though, he is screaming that he is hungry 

[bmf]

Probably "stiction" being experienced where your fork bushes are binding and knock as they free up, happens when the teflon gets worn. what year do you have ? How many kms?

Sent from my SM-G900W8 using Tapatalk

[Skropi]

Its a 2004 gs500f with 22000kms. Any way to check if it is the fork bushes at fault? In case it is, is it important to solve at once and is it easy to do?

(what part is the "fork bushes"?  )

[Skropi]

Hmmmmm, well, I managed to replicate the knock without having the forks going up and down, or if they go, they go very very slightly. Just holding the front brake and rocking the bike back and forth replicates the "knock knock", which also happens without breaking, on bumps, as well.
I really cant figure this out guys. My last resort will be to take the bike to a mechanic and have him check it out...

[Shepa]

That should be the sound of floating disc (rotor) rivets clicking. Grab the disc with your hand and try to move it clockwise and anticlockwise, and you'll get that sound.
The more freeplay inside rivets, the louder the clicking.

Front brake disc consists of three parts, the mounting part (center, or "the heart" of the disc), and the outer (friction) part, joined together by ring type rivets (the third part), and it must have a certain amount of free play (not much, but still). Hence the expression "floating disc".

It is made that way to prevent overheating and warping of the disc due to heavy braking.


Sent from my toilet seat using HTC FartPhone

[Skropi]

Yep, I did check the disk and found out it is floating. But is it possible to make the knocking sound when not braking?

[Shepa]

Not likely.

Maybe the braking pads are moving slightly?



Sent from my toilet seat using HTC FartPhone

[Skropi]

I am riding it to a mechanic tomorrow morning to check it. If he doesnt find the cause then I will live with it 

[Shepa]

One thing comes to mind...
Check if the floating part of the caliper is moving freely (you'll have to remove the wheel to check that.)

If it's stuck, maybe one of the braking pads is dangling on the pin because it's not pressed to disc while the brake is dissengaged.

Sent from my toilet seat using HTC FartPhone

[peteGS]

Check the torque on the steering stem nut, could be loose which will allow the steering stem to move slightly up/down.

Worst thing there is it will wear your stearing head bearings awfully fast.

My steering head bearings are shot at the moment and I have the same issue exactly but a bit worse... I can feel the knock as it happens, not just hear it (my bearings are 34 years old though!).

[The Buddha]

I have had these things clobber each other/themselves in many of the bikes.
Brake pads, front axle spacer & headlight to ignition lock.

Cool.
Buddha.

[Snake2715]

Not the black rubber that goes along the edge of the tank, but under the front side of the tank is a hook built into the tank. It a glued on. If it is not correctly seated or.of the glue is not holding the tank will knock at the hook and it will sound like the shocks. I would check that again. If you specifically checked that already excuse the redundant post on my phone and may have missed it.

[peteGS]

Any news on a diagnosis yet? Should have a bet on which suggestion is right... 

[Skropi]

No news yet, but I "think" that the k nock comes from the headlight area  I have no idea what exactly to check there though. There is a different knock under braking, it is a double knock to be exact, but that is 99% the floating rotor disk, so no worries there...

[peteGS]

Good luck! Keep us up to date...

[The Buddha]

"Floating rotor" likely wont knock, its not floating out in the middle of nowhere free to hit anything.
Its just a rotor that can move if you - well push it side to side.

Headlight bucket can hit the lock cylinder. Likely harmless, the thing is grommet mounted. You hard mount it that will blow headlight bulbs.

Cool.
Buddha.