1200 front end shimmy


Information and questions on GL1200 Goldwings (1984-1987)
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jeffwhilden
Posts: 1
Joined: Mon Aug 10, 2009 9:46 pm
Location: Craig, CO
Motorcycle: 1985 Aspencade

1200 front end shimmy

Postby jeffwhilden » Sun Jul 04, 2010 5:51 pm



Any ideas on why my 85 has a slight wiggle in the bars when i go down hill with the power off? Also if I take my hands off the bars at 20 or 30 mph the bars take off on a nasty head shake, almost lock to lock. Just trying to zip my jacket and get the **** scared out of me. Thanks Jeff



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WingAdmin
Site Admin
Posts: 17050
Joined: Fri Oct 03, 2008 4:16 pm
Location: Strongsville, OH
Motorcycle: 2000 GL1500 SE
1982 GL1100A Aspencade (sold)
1989 PC800 (wife's!)
1998 XV250 Virago (sold)
2007 Aspen Sentry Trailer

Re: 1200 front end shimmy

Postby WingAdmin » Mon Jul 05, 2010 12:38 pm

It's very common in Goldwings. Have a look at this thread.

jamesamccarty
Posts: 1
Joined: Mon Mar 15, 2010 5:08 pm
Location: Brandon, MS
Motorcycle: 1987 GL1200 Interstate

Re: 1200 front end shimmy

Postby jamesamccarty » Tue Nov 02, 2010 9:07 am

My '86 Aspencade did the same thing. My front tire had a few miles on it, so I decided to replace it. Trouble went away.

jsarette
Posts: 5
Joined: Mon Aug 31, 2015 8:56 pm
Location: Manchester, NH
Motorcycle: 1984 gl1200

Re: 1200 front end shimmy

Postby jsarette » Tue Oct 06, 2015 9:25 pm

I too had a shake when decelerating at slow speeds, if i just ligktly took my grip off the bars the handle bars would go into oscillation. Tried not to let it get to wild else it could tear something up. I replaced both front and rear tires, it was needed. It lessend the shake frequency but still it prevails.
The bike is new to me and I have been busy with her. Didn't check the steering head bearings, but did do the push and pull on the front tire with the bike elevated (tires off the ground), Didn't notice any motion, or displacement when pushing or pulling front to back or siide to side.

What to do...

Jim in NH 84 GL1200I

jsarette
Posts: 5
Joined: Mon Aug 31, 2015 8:56 pm
Location: Manchester, NH
Motorcycle: 1984 gl1200

Re: 1200 front end shimmy - causes - musings

Postby jsarette » Tue Oct 06, 2015 10:19 pm

I'll look at putting dynabeads into front and rear tires.

I think i am getting a picture here of what is happening, physics wise. and for those of you who have watched Twist of the Wrist video on youtube, there may be something to what folks say about rear swing arm (worn, or play in it, or it being misaligned), especially the part where you see the superbike doing a wheelie and then planting the tire back down with a little offsett. The tire is greatly flexing and will seek to straighten out or you could say the bike hunts for equilibrium.

I hear lots of things that helped folks fix their bikes, New tires, new steering head bearings, tightened steering head parts, etc. Has anyone mentioned anything about Front forts contributing to the fix?

1) If both tires are misaligned (in angle) (eg, both tires NOT being in line) this could contribute to oscillation or the hunting for equilibrium.
2) Observation: When we decelerate it is often most noticeable, In this case we are placing more pressure on the front wheel and it's suspension parts.
I suppose the forks not acting the same could contribute, ESPECIALLY if they don't work equally or in unison. Perhaps this is why Fork Brace upgrades work for some folks.
3) How does the oscillation start, well classic oscillation occurs when the system is under-damped. Fork braces help to dampen the oscillation that may be inherent in the design of the bikes, especially after they are broken with years of riding. ( Has any one owned one of these as NEW, and did they oscillate then?)

So, continuing.., the wheels act as gyroscopes, if you are in a turn and add power or take power away, the bike rights itself, wanting to continue and precessing when speed or wheel revolution rate is changed ( remember your Right-hand-rule from Physics?), so the bike stands up... tried it this AM.

But when you are riding straight and decelerating at low speeds, i think if one fork is stronger that the other, the wheel will cant or deflect L or R, then the the gyroscopic forces take over and try to correct for the "Counter-Steer" input given by the force on the forks, turning the wheel back the other direction. If not damped by us grabbing the handlebars again or super fork braces etc. the oscillation will continue to occur, which may cause, cracked welds, broken frame parts or worse a high side flip! So don't leave the those bars unattended!

I hear micro-beads are used to abate this, I would guess they are thrown back and forth in the tire to dampen the oscillation.
It has been found to work, so we are still not attacking the root cause, but something is better than nothing i guess.

Does this problem occur on other motorcycles, super-bikes, crotch-rockets, and why not?

I hope this gives others some fuel to go out and find the root cause in the design. I don't have the time to spend, on this one issue, but I know some folks do.

Cheers
Jim in NH 1984 GL1200

BTW I enjoyed a beautiful ( Hands-On) morning ride and a scenic return home in the Fall leaves starting to show some great colors. Lol,

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WingAdmin
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Posts: 17050
Joined: Fri Oct 03, 2008 4:16 pm
Location: Strongsville, OH
Motorcycle: 2000 GL1500 SE
1982 GL1100A Aspencade (sold)
1989 PC800 (wife's!)
1998 XV250 Virago (sold)
2007 Aspen Sentry Trailer

Re: 1200 front end shimmy

Postby WingAdmin » Wed Oct 07, 2015 8:46 am

This is a problem that has to be overcome by every motorcycle designer. There are many different ways to dampen oscillations, just as there are many different causes.

The steering system is designed such that the resonant frequency of the system is below that which would be triggered by rapid displacement by the tire on the road. However, there are SO many things that can change this - any looseness in the front forks, wheel, wheel bearings, front suspension geometry, fork compression, steering head, rear wheel bearings, rear swingarm, rear shock wear, load, center of gravity, etc...will raise that frequency into the area where it will occur.

On GL1100's, they originally came with a headlight hanging off the front. When the faired GL1100's came along, that headlight went away, which raised the resonant frequency significantly, so a heavy steel weight was placed on the steering head in place of the headlight.

Bar-end weights can help, as they have a large moment (distance from the pivot) and a small weight can therefore have a large effect towards lowering that resonant frequency.

The gold standard, used by racing bikes and many sport bikes, is a steering damper - an adjustable friction device that works like a "friction lock" for the steering system - it makes it more difficult to turn the handlebars. This is very important for these types of bikes that have extremely short trail, giving them quick steering, but making them very susceptible to speed wobble.

There is an aftermarket steering damper available for GL1800's...but it is very expensive.

Your best bet is to start by going over your bike from front to back and tightening everything to spec. When my GL1100 developed a high speed weave, I ended up finding the cause was incorrect installation of swingarm pivots by a previous owner, causing too much lateral free play on the swingarm. Once I installed and torqued them correctly, the weave went away.

Boatswain62
Posts: 4
Joined: Wed Aug 05, 2015 2:08 pm
Location: Olalla, WA
Motorcycle: 1986 Aspencade

Re: 1200 front end shimmy

Postby Boatswain62 » Sat Oct 17, 2015 5:39 pm

My 86 Aspencade had the wobble. Repaired seals, New tires, and beads. She rides smooth, smooth.
I did a lot of research on dynabeads and the like. (Not an advertisement) but go to

Www.checkeredflagtires.com

My research rested with them. Very good info. It is best by far to put them in at a tire change. They also send along an instruction sheet to your mechanics(easy on the oil etc).

These are superior quality,guaranteed and inexpensive to boot.
Ride safe
Boatswain62

LONEWOLFPS
Posts: 5
Joined: Mon Nov 23, 2015 3:48 pm
Location: Wurtsboro,Ny
Motorcycle: 1983 Honda GL1100i/1985 Honda GL1200 LTD/1987 Harley 883

Re: 1200 front end shimmy

Postby LONEWOLFPS » Fri Dec 11, 2015 6:48 pm

I remember this doing it on Hondas in the 70's...nothing new really....balancing tires as most do not...forks need to be set properly...tire pressure...So many things can contribute to it....Fork Braces? Well the 1100I has one and it will do it if all is not correct...I found mine to be that the steering was a bit too "FREE" adjusted to proper torque and it went away...




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