Slow speed shimmy/change of direction

[Super_v500]

Right, I've been looking but can't find anything...

I get a very small wobble on my 89 when commuting, when filtering/lane splitting, it feels as if the bike isn't planted, it sometimes takes a bigger push to get it to drop in to move the bike to the left, or sometimes it wants to fall in.... Feels like the tyres are in a bowl.

So far I've checked: handlebar straightness, wheel bearings, swing arm bearings, wheel alignment and fitted new head bearings, tyres are in good condition bt45s with no signs of cupping or squaring.

Happens on the flattest and smoothest of Tarmac...

Baffled....

[nurse]

Have experienced something similar when rolling slow up to traffic lights.  Have matched front and rear tyres in the last week so will let you know if I find any difference.  Also have put on 3.5" front wheel so will also let you know if this changes anything.

I did wonder if it was the changes in road surface wear, tyre grooves etc may contribute?

[andyb]

Air pressure wasn't mentioned, but I'm assuming you checked that as well.

Has this been ongoing since putting these tires on, or is it a more recent thing?

[Super_v500]

Air pressures have been checked, tyres have been on since I purchased it, was having no problems until about 150 miles ago.

[FJmonkey]

Grasping at straws here but tires can have internal failures. More often a bad tire from the factory but that problem is normally felt right a way, not miles later. Still possible though. Try a higher pressure in the tires as a test on a test ride, not for your commute. A few pounds at a time. The higher pressure will remove the influence a tire has to track. If it is the tire, the problem will be less pronounced. It also reduces the contact patch and traction, hence for test rides only, not in traffic. Test the front first then with normal tire pressure in the front try the rear. The test is easy, cost nearly nothing and it will at least remove the tires as a variable in your hunt for root cause. 

[Super_v500]

Could it be that the top yokes are out of line?  I'm currently in the process of stripping the back end off the bike to have a looksie if it's anything back there.

[Pat Conlon]

Check the torque on the stem nut.

[racerman_27410]

I'm going to cast my vote for a tire issue..... the only time i've ever felt anything like described  was when i had  bad tire.

like maybe a cord broke internally.

You said the tires have been on the bike since you got it...what brand tires and how many miles/years has that been?



KOokaloo!

[markmartin]

Check the torque on the stem nut.

I agree.  I had a KDX 250 back in the day, and it handled ruts in the trails terribly (wouldn't let me out of them) until a friend with more mechanical experience adjusted (loosened) the stem nut.  It handled fine after that.  I know this is a slightly different circumstance but for what it's worth, (free)  I'd try it.

[RichBaker]

Could be the steering head bearings are too tight.... If you adjust them so they're perfect, then torque the top nut (the one on top of the upper triple) to its 110 #/ft(IIRC), the bearings end up WAY too tight. I ended up leaving them a little loose, then after torquing the top nut, they were about perfect.

[FJmonkey]

Could be the steering head bearings are too tight.... If you adjust them so they're perfect, then torque the top nut (the one on top of the upper triple) to its 110 #/ft(IIRC), the bearings end up WAY too tight. I ended up leaving them a little loose, then after torquing the top nut, they were about perfect.

So leaving your steering stem nut(s) loose is better than too tight???

[RichBaker]

too tight and the bike wanders, you overcorrect because it's slow to react to steering input, etc.....

If you read my post, you'll see that the "fall test" is perfect after torquing the upper nut. Comes down to tolerances in the threads, basically. Set the bearing preload so it is correct without the upper triple and nut torqued, they get too tight when the rest is bolted on...IIRC, the upper nut torque spec is 110 lbs/ft.   

[FJmonkey]

too tight and the bike wanders, you overcorrect because it's slow to react to steering input, etc.....

If you read my post, you'll see that the "fall test" is perfect after torquing the upper nut. Comes down to tolerances in the threads, basically. Set the bearing preload so it is correct without the upper triple and nut torqued, they get too tight when the rest is bolted on...IIRC, the upper nut torque spec is 110 lbs/ft.   

Ok, seems like the torque spec is too tight, reduces the bike's natural effect to adapt to changes in conditions. So back off just a tad and the natural adjustment is returned to what should be normal. Right?

[RichBaker]

Yep, back off the adjusting nuts and torque the top nut to spec....  I set my adj. nuts so they barely contact the bearing race, then put the triple on and torque the upper nut to spec. She passes the "fall test" and handles great. I could be wrong about the torque I'm stating, I don't have my manual handy...  I do recall it being fairly high, though.

[Harvy]

Yep, back off the adjusting nuts and torque the top nut to spec....  I set my adj. nuts so they barely contact the bearing race, then put the triple on and torque the upper nut to spec. She passes the "fall test" and handles great. I could be wrong about the torque I'm stating, I don't have my manual handy...  I do recall it being fairly high, though.

Rich, my take on this is that the initial torquing of the adjuster nut is to seat the top and bottom bearings. From memory, the Clymers than says to back the nut off and then take it down so that you get a good bounce in both directions.
As to the top nut - I could not for the life of me figure out why you would want such a high torque figure. The top triple is held in position by its clamp on the top of the forks - I personally just nip the top acorn nut down so that it is just passed seated - like a 1/4 of a turn...... never had a problem with it coming loose and don't have any steering problems either.

Harvy