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Need help with high(ish) speed wobble

Yellomantis

Yellomantis

Husqvarna
I wasn't sure where to post this, so I just stuck it here.

First, a little background. The bike has approx 5000 miles on it, and I did a few changes all at the same time, not thinking they would make a difference. Before I made all the changes, I have had the bike up to 88 mph with no problems at all, now, the front end starts this horrible death wobble at around 62 mph, and it progressively gets worse until it feels like the bike is going to huck me off to one side. When I bought the bike, the front tire was almost gone, and the rear tire was a new Kenda. All riding has been on pavement thus far.

Here's a list of what I did:

Acerbis Cyclops headlight
new Pirelli Scorpion Rally tires front and rear
new front tube
rim lock in the rear
42 tooth rear sprocket, trimmed chain and adjusted
adjusted the rear sag (as an attempt at fixing the wobble)

Neither of the wheels/tires were balanced, the original ones weren't, so I didn't see the need to balance the new ones...

The tires had 35psi (front) and 40psi (rear) when I got them back from the tire shop. I dropped the pressures to 25psi, then to 20psi, and finally I'm at 15 psi front and 20 psi rear. Each time I dropped the pressures, a small bit of the wobble went away. I took a screwdriver and rung out the spokes on both wheels and they all have the same tone. The wheels looked true when I spun them on the bike.

Now, the question at hand, has anyone encountered this on their bikes? I keep getting told to buy a steering dampener, but I believe that will just mask the problem at hand rather than fixing it and I don't want to throw a $400 part at the bike hoping to cure the problem which wasn't there before the changes...

PLEASE HELP! I want to get back on the bike!
 
I had a guy give me a tire, 21" Metzler, it was cast out of round, my previously balanced front rim went crazy, until I got rid of that damn tire. Try another tire, even a worn out one, see if it feels the same. I would also suggest balancing your front wheel/tire, it's made all the difference for me.

WheelBalanced.jpg
 
My 630 had a bad high speed wobble. Tried the lot: front and rear higher and lower settings etc. etc. etc. In the end I had the tyres balanced by an expert. He took a lot of trouble ... and THE WOBBLE´S GONE.
 
I'm sure you checked this, but sometimes we overlook the obvious. The rear wheel is set in place straight, right?
You didn't mention anything about the steering head, but the bearing has just a little preload?
If the tire was distorted/out of round enough to cause that much trouble, I would think you could tell when you spun it.
Keep looking you will find it. Some of the 630 owners chased a headshake for a long time but the 610s are much better in that respect.
 
What is the position of the fork tubes in the triples? You can get the same effect of increasing sag by dropping the fork tubes flush with the triples. You won't have as good of turn in, but you will be more stable in loose dirt/sand.
 
Xcuvator said:
I'm sure you checked this, but sometimes we overlook the obvious. The rear wheel is set in place straight, right?
You didn't mention anything about the steering head, but the bearing has just a little preload?
If the tire was distorted/out of round enough to cause that much trouble, I would think you could tell when you spun it.
Keep looking you will find it. Some of the 630 owners chased a headshake for a long time but the 610s are much better in that respect.
Click to expand...

When I did the new rear sprocket, I went down to a 42T. I removed one link on the chain and adjusted the rear wheel accordingly. Right now it is on the second to the last notch on the swing arm, even on both sides...

I didn't touch the steering head, how do I check for the bearing preload?
 
jon6.0 said:
What is the position of the fork tubes in the triples? You can get the same effect of increasing sag by dropping the fork tubes flush with the triples. You won't have as good of turn in, but you will be more stable in loose dirt/sand.
Click to expand...

The fork tubes are 2mm out of the upper triples. I'm going to set them flush today and see what happens. Would 2mm make a difference?
 
Yellomantis said:
When I did the new rear sprocket, I went down to a 42T. I removed one link on the chain and adjusted the rear wheel accordingly. Right now it is on the second to the last notch on the swing arm, even on both sides...

I didn't touch the steering head, how do I check for the bearing preload?
Click to expand...

With the front wheel off the ground there should be just a little turning resistance so that when you turn the bars from straight and let go, that the front end doesn't freefall and clunk on the steering stops. As a general rule, a bearing that is too tight will cause the bike to wander at low speed and a loose bearing can cause the bike to wobble or headshake at high speed.
To adjust it, loosen either the top of bottom slider pinch bolts and loosen the top nut on the top triple clamp then the slotted adjuster nut can be turned with a punch and hammer. It might take a couple trys, because when you retighten the top nut it will tighten your adjustment a little bit.
 
Xcuvator said:
With the front wheel off the ground there should be just a little turning resistance so that when you turn the bars from straight and let go, that the front end doesn't freefall and clunk on the steering stops. As a general rule, a bearing that is too tight will cause the bike to wander at low speed and a loose bearing can cause the bike to wobble or headshake at high speed.
To adjust it, loosen either the top of bottom slider pinch bolts and loosen the top nut on the top triple clamp then the slotted adjuster nut can be turned with a punch and hammer. It might take a couple trys, because when you retighten the top nut it will tighten your adjustment a little bit.
Click to expand...

I'll have to give that a try. Just got to figure out what a spider pinch bolt is now... LOL! It has almost no preload. I'm sure the bearings could use a good repack anyway. If I have time next weekend, I'll tear it down.

On the plus side, 95% of the headshake is gone! I added another 1/2" of sag to the rear (now at 4.5") and dropped the front fork tubes flush with the upper triples. Now if only shakes a little above 80mph. All I have to do to correct it is apply a little pressure to the bars and it goes away. Guess I'll be getting a steering stabilizer sooner than I thought...

THANKS FOR THE HELP GUYS!!!:applause:
 
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