What the fork!?

[twangin4u]

My front forks are gonna get me killed. Everybody complained about the anti dive forks but my 84 handled pretty sweet compared to this bike. I could ride with confidence. If I get up to 80-90 mph it doesn't take much and the bike want to go into a suicide swerve. Even when I was trying different setting and different oils in my 84 it never acted anything like this. I almost don't even want to ride it cause it's gonna be bad if some bad luck intervenes. Anybody got any suggestions? Besides buying new forks. Lol

[aviationfred]

Have you had the forks apart since purchasing the bike?

  I have seen some amazing posts concerning forks on various online forums and on facebook. I have heard about different springs being found in forks. One fork overfilled with oil, the other almost dry. One fork with a spacer and the other with no spacer.

Sounds like a total rebuild is in order.

Fred

[oldktmdude]

   Is this the same bike you were having steering problems with before? If it is, it sounds like you have not tightened the steering head bearings to the
correct torque specification or the bearings have some damage.

[twangin4u]

Everything's torqued correctly now. I've gotten the wobble a lot better but still there at high speeds. At 95mph is starts. It's almost an aerodynamic thing. If I'm sitting up it will wobble but if I'm hug the bike and lay down it's not too bad. Still a little sketchy tho. I noticed when the bike had day for many years the master cylinder on clutch leaked and dropped down which dissolved some of the ferring by where it scoops air into the motor. I wondered if it was causing the air scoop unevenly and maybe cause the bike to wobble but I don't know

[FJmonkey]

Everything's torqued correctly now. I've gotten the wobble a lot better but still there at high speeds. At 95mph is starts. It's almost an aerodynamic thing. If I'm sitting up it will wobble but if I'm hug the bike and lay down it's not too bad. Still a little sketchy tho. I noticed when the bike had day for many years the master cylinder on clutch leaked and dropped down which dissolved some of the ferring by where it scoops air into the motor. I wondered if it was causing the air scoop unevenly and maybe cause the bike to wobble but I don't know

The air passing under the bike where the lower chin scoop is not likely to cause a speed wobble. The most common issue is a cupped/worn front tire. My last speed wobble was minor, I decided to wait till after a new front tire. No more wobble.

[chiz]

I have had perfectly good looking tire behave horribly at a certain speed on a car I cant see why a shifted belt on a bike tire might have the same effect.
Lez

[Capn Ron]

Others are covering this topic well.  The front end only has a few things that can cause it to speed wobble.  As far as a front tire is concerned, heed the Monkey.  In the two mid-speed wobble cases on my FJ, the initial oscillation was started by a bad front tire and exacerbated by the headset not being adjusted properly (too loose).  Others have mentioned fork issues and down at RPM a few months ago, we took apart two sets of forks and neither one of them were set up correctly from previous owners!   

As far as your thinking on aerodynamics having a part, think about this.  When you are hugging the tank, your weight is shifted forward putting more weight on the front end.  When you sit upright, you are also shifting your weight back and off the front end...AND you're head and chest are catching some of that 95 MPH wind further lightening the front end.  My speed wobble on the way up to the 2014 West Coast Rally changed dramatically (for the better), by off-loading my three Givi hard cases.  They all sit behind the rear axle, so their weight lightens the front end.  Replacing the (perfectly good looking) front tire the next day cured 90% of the wobble and snugging up the headset bearings eliminated the remaining 10%

I did catch a high-speed wobble going down highway 2 into Glendale, CA back in college.  I estimate I was going well over 100 (my speedo only went to 85) and I got the tank-slapper speed wobble.  It was so bad, my first course of action was to pick a place to crash and likely die.  Scary stuff!

[simi_ed]

OK, let me add another thought.  If you are still running the OEM fork springs (or Progressive springs) that are sacked this could cause the wobble you're describing.  If the forks are well into their 5-ish inches of travel the head angle is potentially very steep.  This can decrease the stability of the system, increaseing the possibility of wobble/oscillation.  As others here have mentioned, look into your forks!

[simi_ed]

OK, let me add another thought.  If you are still running the OEM fork springs (or Progressive springs) that are sacked this could cause the wobble you're describing.  If the forks are well into their 5-ish inches of travel the head angle is potentially very steep.  This can decrease the stability of the system, increaseing the possibility of wobble/oscillation.  As others here have mentioned, look into your forks!

Let me explain:  I had a Suziki GS1100E before my FJ.  i had changed out the rear shocks for a set of 3/4" longer units to speed up the steering response and gain some ground clearance.  This all worked well, but the bike became an unruly tank slapper above 80-90 mph.  I then proceeded to add a steering damper to calm down the speed wobble.  Moved the tankslapper up to 120 mph+, but he steering effort at all speeds was unbearable.  Good thing it was an adjustable damper, but I had to remember to crank the damper before cranking the throttle!
Meanwhile I never touched the front forks.  Springs were sacked, static spring sag was probably 40-60 mm (of ~120 mm total travel).  In retrospect this was a huge oversight on my part.  

[twangin4u]

Everything's torqued correctly now. I've gotten the wobble a lot better but still there at high speeds. At 95mph is starts. It's almost an aerodynamic thing. If I'm sitting up it will wobble but if I'm hug the bike and lay down it's not too bad. Still a little sketchy tho. I noticed when the bike had day for many years the master cylinder on clutch leaked and dropped down which dissolved some of the ferring by where it scoops air into the motor. I wondered if it was causing the air scoop unevenly and maybe cause the bike to wobble but I don't know

The air passing under the bike where the lower chin scoop is not likely to cause a speed wobble. The most common issue is a cupped/worn front tire. My last speed wobble was minor, I decided to wait till after a new front tire. No more wobble.

My first thought was the tires wear as well. So I swapped out for another tire. Same results. Actually a little worse maybe. I appreciate all the input. Everyone's Experience saves me some time and frustration of guessing and error. I'll be sure to share what I find solves it for me. Thanks

[FJmonkey]

My first thought was the tires wear as well. So I swapped out for another tire. Same results. Actually a little worse maybe. I appreciate all the input. Everyone's Experience saves me some time and frustration of guessing and error. I'll be sure to share what I find solves it for me. Thanks

Was the swap with a new tire? Or different tire?

[racerrad8]

FYI, I think I have a new Avon 3D XM at the shop. I ordered a 17 when I needed a 16.

I'll make you a great deal on it.

I'll look tomorrow.

Randy - RPM

[ribbert]

My first thought was the tires wear as well. So I swapped out for another tire. Same results. Actually a little worse maybe. I appreciate all the input. Everyone's Experience saves me some time and frustration of guessing and error. I'll be sure to share what I find solves it for me. Thanks

[/quote]

Do you have a top box fitted?

Noel