My bikes become a bit tankslap-happy

[mike-s]

I've started to notice that my bike's become a bit headshaky/tankslappery of late.
early symptoms include when going downhill in my street (big fuckoff hill) at about 20ish km/h with only my right hand on the bars, i back off, and the bars get a bit headshaky.

Later symptoms include twitchiness when going over bumps, but tonight was the big one, i went out of the driveway at work, over a slight rise in the road outside work under reasonably hard acceleration. The front goes up about a half foot or less in the air and goes down again just as quickly.

The problem is as soon as the front goes on the ground again the bars start violently shaking from side to side in a tankslapper. i squeezed on the power and came out of it after 2-3 seconds of shatting my pants.

The thing is, wtf could have changed to have caused this to start happening more and more? The things that have changed over time are
1) new fork oil, but i measured it and its all ok, only other thing is it was happening before i changed it.
2) slightly worn tyre, doesnt look off, is an evenly worn shape, but it wouldnt surprise me if that was the problem
3) i was running on vapour tonight and was nearly on empty when it happened (but its wiggled on me, even with a reasonably full tank)
4) i hear a slightly holow kathunk going over bumps, etc.. im going to take the wheel guard off tomorrow to make sure that it's not a loose easher, but what's the chances that its partly caused by a rooted wheel bearing?

any other ideas? oh and while i remember, im pretty certain my headstem bearings are nice and solid, no forward backward or side to side notchiness that i can ascertain.

[Barrabob]

I have come to believe that its caused by not enough weight over the front wheel which could be a variety of things.

Is it a bit stiffer up front after the forkoil change??

you really need the front softer than the back or it doesnt want to compress at the right time and skips off the surface of roadand you get the dreaded wobble ask hemi.

try adding a little preload at the rear or lift it a mm or 2 to bring the weight bias foward a little just watch that lifting it doesnt take too much weight off the back if you go down that road.

Could be barking up the wrong tree of course thats just what i have found fiddling with my bike, if the front end is unloaded it triys to skip off the road surface and has itself a slapper so adjust geometry so its driving the front more into the bitumen

most of those setup guides recomend adding front preload but that flies in the face of my recomendations.

would be looking at softening the front a bit or stiffening the rear , Hows the back shock???

what sort of bike is it mike??

[mike-s]

The backs a bit stiff as ive upped the preload a notch from standard, so it acts very stiff when its just me, but nice soft & lazy when i've got my missus on the back (but the rear of the bike isnt too wallowy).

Mind you i did put 15wt oil in the forks.... so its very responsive, and sometimes it feels a little springy, that might be part of my problem then *ponders*

[photomike666]

I have come to believe that its caused by not enough weight over the front wheel which could be a variety of things.

Are you suggesting Mike has put on weight?

I find my 6 gets light at the front when I load the topbox, but usually only enough to vibrate the bars when I take both hands off.

The fork oil might have accentuated the problem, but if you had it before it's probably not the root cause.

As well as checking suspension, look at wheel bearings (front & back) and headstock bearings too. Your hollow thunk sounds like movement somewhere (I'm assuming the forks aren't bottoming out).

[mike-s]

the bikes had the thunk sound since day one, but its only now getting that little bit more noticeable (smaller bumps get it doing it now) im plannin on jackin the front up and havin a look sometime this weekend while i try and track down the source of a f*in oil leak as well.......

[Duane]

Just ride it mate, ask ron, he dropped a tooth and his bike tankslaps him when he's going to the milkbar to pick up a loaf of bread.

[Smitty]

I've started to notice that my bike's become a bit headshaky/tankslappery of late.
..snip...
4) i hear a slightly holow kathunk going over bumps, etc.. im going to take the wheel guard off tomorrow to make sure that it's not a loose easher, but what's the chances that its partly caused by a rooted wheel bearing?

any other ideas? oh and while i remember, im pretty certain my headstem bearings are nice and solid, no forward backward or side to side notchiness that i can ascertain.

Mike
mine started doing that late last year
and I thought wheel bearing
but
it was head stem bearing
which felt nice and snug not notchy but when looked
at, was actually shite
replaced them and the shakes went away
'til the tyre scalloped out a month or 2 later

2 months later i bought a 12

[FrogZ]

This is posted elsewhere but.
1. What are thre tyres like ? Tyre pressures ?
2. Head bearings OK
3. Undo all the bolts except the top triple on the forks (including brake caliper bolts) bounce front under brakes, retighten
(sometimes the fronts get twisted, expec. if you cross up wheelstands
4. Wheel balance

[Glen]

I was gonna say steering head bearings Mike but when I say it now it just sounds like an echo.

Something has clearly changed over time with minimal other changes from yourself so I'd reckon Smitty and whoever else has said bearings is pretty right.

Grab your bars lock your front brake on and bounce the bugger up and down as hard as you can, you'll likely hear a clunking noise or feel some movement.

[mike-s]

well it could be headstem bearings as i said, there is that thunky noise when i hit gutters, i initially thought it was something down in the wheel guard, but as its a distinct clunk, it *may* be the headstems :-\.

better go read up on htf to replace those feckin things to see if i can d.i.y, otherwise my bike shop's gonna be getting some $ offa me...


my todo list now consists of engine cover seals, maybe wheel bearing maybe headstem. I'd rather it be wheel bearings, actually, the thought of catastrophic failure makes me prefer the idea of headstem..... either way, cheers for the advice *goes off to hunt for the manual*

[Smitty]

well it could be headstem bearings as i said, there is that thunky noise when i hit gutters, i initially thought it was something down in the wheel guard, but as its a distinct clunk, it *may* be the headstems :-\.

Mike
check the w/bearings
but it would be unusual..my GeePeeX wheel bearings
were good at 70,000... the headstem were not

other things to check
have you got the antirattle plates behind the front brake pads?
make sure the f/guard has not cracked at the mounting points
(the geepeex are notorious for that)

hth

[mike-s]

Mike
check the w/bearings
but it would be unusual..my GeePeeX wheel bearings
were good at 70,000... the headstem were not

hmm, the fact im just pushing 90kkm leans towards it being the headstem bearings, will still check them both.

other things to check
have you got the antirattle plates behind the front brake pads?

yup, both of 'em.

make sure the f/guard has not cracked at the mounting points
(the geepeex are notorious for that)

One of the first things i did was fix a couple of big cracks in the guard, one on each side of the doubleback around the forks. There were fracture cracks on the front lip of the guard as well. I sanded back all the paint to the plastic and did what has since turned out to be an awesome fibreglassing job on it

cheers for the tips though. aside from the bearings theres a loose washer possibility, but its always done it, so i think theres something possibly up with the h-s or wheel bearings...