Front end shimmy, need advice

Hey guys,
Have a front end wobble, most notable when I loosen my grip on handlebars. Not an issue while driving normally. New tires mounted a few months ago, condition was present before and after tire mounting.
Front forks removed while bringing bike back to life, wondering if that has contributed to condition.
Bike has about 10k miles.
Any thoughts are appreciated.
Thanks!

 

OK, I'll give you partial advice, but there are more experienced experts who will chime in -- This is based on my experience:

First, "letting go" is dnagerous.

Second, (and I saw this from someone else, but don't remember who) -- but, your triple is (likely) not perfectly aligned to the bottom fork holder -- what I did (again some one else's idea) -- when I rebuilt my front end including new bearnings -- was to use a plate of glass which I placed over the front of the triple and the lower fork retainer to ensure their alignment "on the same plane" while carefully, slowly tightening the fork-bolts and the triple bolts...

However, I am also going to guess that not only may the alignment be off, but if you have a "kink" or "flat" spot in your turn bearings at or near center, that the steering may continuously "hunt" for that spot once your "loosen" your grip. So, a bearing change may or may not (also) be required.

Hope this helps

 

At 10K miles it "shouldn't" be swingarm bushings or steering head bearings or even wheel bearings, so the top of the list is - -

Incorrect front wheel balance, or the tire bead didn't seat "true".
Spin it, and see if the tire hops or moves laterally - did you watch them balance it??

Did you tighten the steering head enough??

 

Just a reference -- not to refute -- my bike had 10.5k miles on it (1981) when I started rebuild, and the head bearings had noticeable "flat spot".

 

thanks for the replies fellas!
i assure you i don't let go of my handlebars ever...i merely loosened my grip to confirm the tremors i felt while riding.
having the tire re-balanced is definitely a step i'll take if need be but because the condition was present before and after the new tire was mounted, i'm putting that option lower on the list. i should also offer the tremor is barely noticeable while riding and doesn't seem to change intensity with speed.
reading your replies confirmed a suspicion i had about re-mounting the tubes and how to insure they're "square" with the wheel. i think i'll loosen everything and tighten the wheels FIRST hoping they'll find alignment and THEN tighten the triple connections. i'm pretty sure i did that backwards when re-mounting the new tire and wheel.
checking the tire/wheel trueness as well as putting the bearings on the list are excellent ideas.
thanks so much for your help guys!

 

I think you're going to find it's the steering head bearing.

Put it on the center stand and throw a fat chick on back so the front wheel comes up. Gently swing the bars back and forth around straight ahead. If you feel a slight catch it's the bearing.

If you don't feel a catch go in front of the bike, grab the wheel and move it forward/backward and up/down. You shouldn't feel any play. If you do you need to investigate more to see if it's wheel bearings or forks, but if not it'll be the steering bearing.

 

I had to change one of the forks seals last fall, the one I couldn't replace when doing the process a couple years back but it wasn't leaking so I bypassed it. Anyway, after that I was starting to notice that when I loosened my grip that the front end started to wobble the longer I kept a relaxed grip. Not 100% sure here, but i'm guessing that either the fork I just put the new seal in and refilled with oil is either A.) Not quite aligned with the other fork, which is less likely, or B.) I filled this fork with a little more oil than the other, so this shock may be a tad more stiff etc. Since I put the bike away and am out of the state until May I won't know for sure, but just my 10 cents.

 

well, i couldn't find any fat chicks (they must stay in on sundays) so i simply jacked up the frame and elevated the front tire and forks. i tried hard to feel any catch or bump when moving handlebars side to side but couldn't find any. also tried moving the front wheel up, down, back, and forth but no play.
i'm going to loosen all fasteners on the front fork tubes and wheel axle. then i'm going to tighten the wheel axle first and then move my way up the tubes. i'm thinking this may align the tubes with the wheel and eliminate the wobble. will post findings.....

 

well, ain't really inclined to take a test ride today as it's pretty cold but i have loosened and re-tightened the front tube and wheel bolts. not confident that's the fix as i found the wheel to not be true...meaning when i hold a straight edge against side of the wheel and rotate it, there is definitely a pronounced out-of plane variance noted. what i mean is that the wheel distorts to 1 side and back in when it rotates. it's not dramatic but enough to easily notice when using the method described.
no signs of impact or such, could've been cast this way. not sure if another try at wheel balancing will help or not but maybe.
hmmmm.....

 

interesting post about the fork fluid possibly having an effect on front end stability. would've never thought about that, thanks for posting!

 

I'm no pro, but the rim is cast, then machined. You found a bent rim, congradulations. A wall trophy for the Man-Cave !! They are cheep on E-Bay.

 

Did you check the run out against both the tyre and rim, or just the trye?

 

If your fork seals are shot and the fork is just bouncing all over the place it will very much affect front end stability as well as braking.

If your rear shocks are worn out or your swingarm bushings are loose it can make the front end wobble. As can the aforementioned steering head bearings.

However, if you have a bent RIM (not just a tire mounted unevenly) then you need to replace it. Allowable "runout" is 2mm vertical, 2mm lateral. If it wobbles more than by 2mm, find another wheel.

 

i checked runout against rim, not tire. it MAY be within the 2mm allowable, i'll check it tomorrow with proper instruments. i'll check tire as well. fork seals appear fine but of course, the tubes could be dry. rear springs are pretty stiff but i will check swingarm tomorrow as well.
i'm assuming to check play in rear end is similar to checking front.....elevate wheel, check side to side play and such, right?

 

Level the bike on its Center Stand.
Have someone hold-down the Rear Seat so you can check the Steering Head.
Move the Steering Head from lock -to- lock observing how smoothly the Bars transition from side-to-side.

The motion should be as smooth as silk and without the least resistance.
Any drag, stutter, bind ::: (no matter how slight) ::: indicates that the Bearings need to be replaced.

Any hitch in the smoothness will cause the front-end to wobble.
The wobble is caused by the inability of the Steering Head to allow the bike to effortlessly track-along making imperceptible corrections to the gyro-forces at work creating stability.

 

I would go to the steering stem bearings first, personally.

Dave F