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-98 VFR800, knocking feeling during braking/bumps


bazke

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Hi everyone!

 

I recently switched to a VFR and I'm loving every minute of it. One day I was a bit too eager to get going and... forgot the disc lock. The "inside" part of the disc got a bit bent so I replaced the disc. I did however have to ride the bike with a bent disc for a bit, maybe 30 miles or so. 

 

Now with the new disc in place I can feel a knock in the handlebars when I either brake decently hard or go over a bump. Going over a bump only gets one knock but braking makes a rhythmic knocking.

 

Initial reading suggested steering head bearings so I lifted the front up and turned left and right slowly without feeling anything different. I also jiggled everything I could but there it doesn't seem anything is loose. Could it be that I screwed up the brake pads by riding with a messed up disc? Right side (old disc) has even pad wear while the right side, the one I replaced, has one pad a lot more worn than the other. I have new ones on the way anyway but I'm not sure this is the issue.

 

Do you know of any other possibility, or some other test I can do?

 

In short:

  • Started with disc lock in
  • Replaced rotor
  • Knocking sound while braking (rhythmic) and over bumps (single knock)
  • No odd feeling while turning handle

 

Any thoughts or ideas would be much appreciated as I'm stumped and not even sure if it's safe riding :(

 

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I went out and bounced the front with brakes applied and the knocking comes when the suspension is on the way back up. After a while the knocking went away and turned in to more of a squeaking sound.

 

edit: It's only there when bouncing using the front brake. Holding rear brake and bouncing the front is nice and smooth.

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Most probably it's coming from the secondary master cylinder (normal).

There can also be a bit of back and forth play on the floating disks. 

Another option could be worn sliders on the front forks. 

How long since forks were rebuilt?

to check this you really need to remove the front wheel and hold the top of the fork lowers and push the bottom of them back and forth. 

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8 hours ago, VFROZ said:

Most probably it's coming from the secondary master cylinder (normal).

There can also be a bit of back and forth play on the floating disks. 

Another option could be worn sliders on the front forks. 

How long since forks were rebuilt?

to check this you really need to remove the front wheel and hold the top of the fork lowers and push the bottom of them back and forth. 

Thank you for the reply!

 

I'm not sure when (or even if) the forks were rebuilt. If I wait until winter to do it do you think I will cause more damage? And when pushing the forks what am I looking for? I guess maybe any kind of free movement that isn't "smooth"?

 

I yanked the discs a bit and with only hand strength there doesn't seem to be any play there. Maybe the SMC could also use a rebuild this winter, it has probably never been touched.

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You wont do any more damage.

The disk rotor movement is a clockwise anticlockwise play that can be moved by hand, some get a bit of play there as they get older but that is ok too.

The secondary master cylinder movement is normal and will still be there even if you rebuild it.

The fork sliders (or bushes) wear out with use, and the bottom of the fork lower will move back and forth, this needs to be fixed as it affects steering.

Hold the top of the fork lower, and try and move the bottom back and forth, if you can the sliders need replacing. It is best tested with front wheel removed.

 

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Update! Took the front wheel off to inspect as suggested by you VFROZ. No play or anything from the forks, phew! But getting the weight off the triple tree allowed the handlebars to move more freely and it was clear that it is the steering head bearings causing the knocks. Even though turning left/right was fine (even with the wheel off) I could yank the bars and the knocking comes knocking.

 

Also explains why bumps caused a knock, compressing the shocks let the assembly have some vertical play that shouldn't be there. Since the road isn't perfectly even, heavy front braking also allowed the tree the same movement causing knocks.

 

New tapered bearings are on their way, wish me luck!

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It's always good to find you only need a cheap fix. 

While your wheel is off, check the wheel bearings. 

New bearings and seals from a bearing shop are only around $20. 

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