Bonneville America Forums Forums Technical Forums General Tech violent shimmy

Okay, here’s what happened. On the way to the Nor’ east this year I let go of my bars for a couple of seconds to do something, I forget what it was, but anyway the front wheel started to shimmy back and forth and it kept getting worse until it was so violent that I had to grab the bars. When I did that it stopped and there was no feeling or indication that anything was amiss she handled perfect.. Strange I thought. I attributed it to the Viper windshield I had installed for the trip. I figured the wind was whipping around it causing the wheel to go back and forth. I didn’t think anything of it and I forgot about it until….Last week. I was riding this time no windshield, and I let go of the bars to tighten my helmet strap and it happened again, shaking back and forth faster and faster until I had to grab the bars to avoid a crash. Once again holding onto the bars gave no indication that any thing was amiss she handled perfectly. This happens at between 50&60 mph. If I let go of the bars at a slower speed say around 35 mph she tracks straight. Now, I can’t seem to stop doing this thinking maybe it won’t happen now, but it does. I’m not really looking for an answer to this problem. I know that it could be caused by a whole host of things and I will have to sort through them to find the answer. What I want to know is… Has anyone else had this problem? Maybe some of you do have it and don’t know it because you have not let go of the bars at 60 mph. Of course if someone does know what causes this and can spare me a lot of checking I would be most grateful. I know the obvious fix is DON’T LET GO OF THE BARS!

Front tires cupped? Rear axle aligned properly?

Mine did that at a lower speed - cupped tires was the cause.

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I know the obvious fix is DON’T LET GO OF THE BARS!

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Right, but that is indicative of a problem. I suggest that you get it sorted out ASAP before something bad happens.
Some other possibilities: Headset bearings loose or damaged, front axle bearings, wheel out of true.
I don't know if a bad chain would transmit vibration to the front like that, but check it anyway.
I expect wheel balance or bad tires would be noticeable all the time, but check them too.

I also get the shimmy at 40mph but only when decellerating. Not real bad, but enough to be an annoyance. New tires, belt drive, total balance and alignment, check front wheel bearings, rear wheel bearings, front steering head bearings nothing was off and nothing cured it.
I think it may be the strange bushings used for the swingarms. They are a pubimeter larger than the axle hole and there is a very small amount of slop there. Every bike I have seen has been the same too. Jojje, the turbo Bonnie drag racing Swede, had the exact same problem and put tiny little shims in the swingarm bushings and it cured it. This winter I'll pull my swing arm axle and do the same. he wrapped once around with some sheet metal (sounds like a job for empty beer can to me) and put it all back together.
I keep my hands on the grips at the time too.

Yer gonna get a PM!
He needs You to empty the can for him!!

I thought you said beer??

Good one Matt!

Mine has the dreaded head shake at 45-50 . Bike only has 2k miles. Dealer is not any help. Denies it exists. it's not a tank slapper, but it is obnoxious.

Mine did that on the way to the Nor'easter and I figered it was my load wasn't balanced. I don't know what speed it was though, so I tried it on the way home and it didn't do it. I try it now every so often and it hasn't done it since. I don't have the answer for ya just the fact that mine has done it and now it don't. Keep us posted on what you check and what cures it when you find it.

I've got the same issue on my Speedmaster. Hands off the bars decelerating and the bars will shake like mad getting worse and worse. This has been happening since the bike was new so I don't think it has anything to do with cupping tires. My Honda VFR also exhibits a little bit of head shake decelerating with the hands off but it doesn't get worse like on the speedmaster.

-Hugh

Re-reading a bike mag (Rider Sep 06 Tech Q&A), there was a tech question regarding the use of radials to replace bias spec tires. The response was that it would probably be ok. They also said factory spec was a better bet. They mention an upside with radials is longevity and more precise handling. Possible downside is oscillation under decel.

My 03 speedy has always had the decel no hands headshake too. Mine however occured between say 50 down to 40mph then would clear up on its on. I tried many things as well even a new tire. No difference. However when I removed the front rim a while back and striped and polished it. then reinstalled the tire and balanced it meself , it seems to have disappeared. Go figure.

Same with my America from new. Tried everything, pressure, balance new tyre then noticed a wobble in only one side of the rim. Eventually got Triumph to replace with a new wheel and been fine ever since.

Mine is doing it too. I'm hoping to bring it to the new dealer here in NH and see what they can do for it. It started on the way home from the Northeast. Must be something in the water out there in NY.

If using the adhesive lead weights, could an unequal number on each side cause wobbling?

Unbalance side to side will cause as much trouble as unbalance top to bottom, just in a different direction. So, yes, it can cause a wobble.
Anyone old enough to remember the old steel wheeled clamp-on sidewalk skates? Turn the skate upside down and give the wheels a spin, and nearly all would shake side to side so badly at to look out of focus, make a loud buzzing noise and stop turning right away because of this.

Anybody ever come up with a solution or real cause for this?
Dinqua did you ever try the shim deal?

I wonder what % of these are using bags or light bars or both. Sounds like wind is dragging on something, we cant have that many cupped tires or out of balance wheels can we?