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Harley Speed Wobble, Tank Slap, also known as the Death Wobble

Hoople said:
Sounds like rear wheel steering caused by rear wheel alignment or engine/transmission rubber mounts being worn & too soft. Perfect rear wheel alignment along with correct axle shims so NO wheel offset exists between front and rear. That is a Must. Perfect rear wheel alignment in relationship to the front wheel is a Must (florescent light tube trick). Add a True-Trac 3 point stabilizer and I would bet you can say good-by to that wobble happening again.

These are the "big hitters" I would absolutely check. There are also a bunch of other secondary reasons how/why that can happen.
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I'm thinking that looseness in the swing arm could contribute to the progression of the wobble. On my last bike, a 1991 Goldwing (sorry I have to mention a rice burner!) there was a square chunk of metal weight attached between the forks to prevent wobble. The only time I had a wobble with that bike was when I clipped a plastic traffic marker (one of those red drum type things) that some jerk put in the middle of a highway curve not seen in the darkness. All I did was pull back as hard as I could to stop the handle bars from doing their dance. For a Harley to wobble, I can only think of looseness in the steering head, the wheel bearings, or the swing arm to cause it....unless, of course, you clip something with the handle bars.
 
CropdusterDoug said:
I'm thinking that looseness in the swing arm could contribute to the progression of the wobble.
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Without a doubt looseness in the swing arm would not be good. I think the worse setup is really on a Dyna such as mine. When I look at what actually holds the entire bike together (two isolation rubber mounts) I can see why there would be major problems when a few parts get old, soft and neglected.

Lots of forces are involved. Some are within your control and some that are not within your control. I think the best approach for safety is to optimize or push in your favor, the ones within your control.
 
This is a condition I've seen many timing on my race bikes, but only once on any of my Harleys.

In a race situation, most times, this occurs when the suspension is "over worked". Meaning you have components working out of sync.

A true tank slapper does not occur all the often in racing. But when it does its because of an out of sync condition. Component failure, rider error or race surface condition all contribute to this. And I've had all of the previously mentioned conditions cause a slapper. Some I've saved, some I haven't. And the get-off is usually a high side, unfortunately.

The one time it happened on my Harley, was on the Road King. And it was my fault. I was in group of folks on a poker run and I broke my own first rule. Don't get near anyone you have never ridden with before.

I was behind a guy on a newer harley with not much riding experience. My bike did not have a windshield, only me and about 20 pounds of stuff split between both saddle bags. We were in a long left hand corner doing 60 mph with a slight bank to the inside of the corner, it was not off-camber.

The guy in front of me did the newbie mistake of going into the corner hotter then he could handle and was on and off the brakes and throttle in the corner. I had planned on passing him in the upcoming straight away and got with in 3 bike lengths of him.

This guy got spooked and stood the bike up and slowed quickly. I had no choice but to let off, jog to the left, get on the throttle and go around him.

In the process, I got the rear and front suspensions working out of sync. The rear was light because of being off throttle, then the front got light because of the acceleration. Light means smaller contact patch and less traction.

All of this, plus the road conditions, cause the slapper to start at the rear and move forward. The rear shook and then that vibration moved forward. It started to get bad as I exited the corner. I relaxed my grip, added some power and it corrected itself. All of this happen in less then 100 feet. And it was rider error on my part.

I run my air pressures, in my suspension, about 5 psi under max, no matter what the load (when they are on the road). This helps stiffen up the suspension and works well. Unfortunatey, harley's have a very numb feel from the suspension. Little or no feedback until it's ready to do something unexpected. Stiffening the suspension helps a little with feel, but not much.

Rider awareness and constant evaluation of what your bike is doing will help you keep it right side up.
 
I had a 2008 Ultra that i had that happen to on 2 seperate occasions. Both to the left and at different speeds but a fairly hard lean. Now this is where my experience as an MSF Instructor came in to save me. Straighten the bike punch the rear bike to stabilize the bike then put it right back into the corner. Never give up on any bike and Practice. You'll be surprised how natural it comes when you need it. I have since traded the bike for a 2010 (love the color couldn't pass it up) but i can tell you that I feel a night and day differencw in the rear end feel. Lot more stable, and a lot more control. No for the soap box. Safety courses are not just for beginners everyone i every helped learned something new they didn't know.
 
SledDog that is probably the best evaluation of the wobble that I have read to date. The situation and stratagy that you used to correct the problem is something we all need to think about. Know your surroundings and the riders you are with, and don't override your conditions or abilities.
Sprint57 you are right on target with the MSF courses. I take one every couple of years to get rid of the bad habits I seem to revert to.
 
I took the course just a few weeks ago and dang I didnt know how to ride! That wobble has occurred with my older 86 flht a few times before i realized tire pressure was low. Now I am going through all the areas you all have said to check. Wish I could find a stabilizer for it but noone lists my yr. Thank you for the advice may save my newbie butt.
 
Really sorry to hear about your loss.

I've only just come across your post so hope this isn't too late.

I bought a low mileage 2003 Anniversary FLHTCUI in 2006.

After a couple of years use it started to develop a problem with a rear wheel wobble.

Several times I was riding along the motorway or A road doing around 60 - 70mph when the rear wheel 'kicked' out. On a couple of occasions this happened whilst cornering. Each time I thought I had a rear wheel puncture and pulled over asap - but each time there was nothing.

After some research on American Harley sites I became convinced it was the deterioration of the rubber mount at the rear end that was causing the problem. Apparently as the rubber (used on the tourers) deteriorates with age it allows lateral movement when under stress.

Additionally, although I'm no technician, I learned that the optimum number of securing points for the rear end unit is five. This apparently prevents any form of lateral movement of the rear wheel. If I'm correct in my understanding my bike only had three anchor points. I believe Harley have now added a fourth.

I imported a device called a TrueTrack and had it fitted.

The first time I rode the Ultra after fitting the difference was staggering. The bike felt so much safer and responsive.

That same day that I picked up my bike from the technician I was involved in an RTA. I was travelling at around 45 mph when a van pulled out of a side road to my left. I was only 15 or so feet away so had little time to react. I managed to swerve the bike enough to save me ploughing into the side of the van, but clipped the front bumper. The bike went one way and i went the other.

I ended up in hospital with a couple of broken limbs but really believe that the TrueTrack saved my life. Without it I'm confident I wouldn't have been able to avoid going straight into the side of the van.

Hope this helps.
 
I have experienced it on a softail deluxe, not sure if were talking about samething. At high speed my frontend wobbled. I took it to dealer and they adjusted head-bolt, it took care of it. I know a few guy's who had loose headbolts with brand new bikes, I quess their was a poor quality control at that plant. One guy it even wore his bearing race for the headbolt out, when they adjusted it improperly. sorry for ur loss. Goodluck
 
This has been an ongoing problem with the Kawasaki Nomad of which I've had 2. The problem is a headset bearing that hasn't been properly torqued from the Factory. When set at the Factory recomended torque there is a front end wobble that occurs if the rider lets go of the bars or during fast acceleration then coming off the throtle too quickly. The other problem being discussed I call a high speed wallow which can and will occur in high speed sweeper turns from many different problems not the least of which are low preassure tires,and missalignment and a few others previously mentioned. I personally believe many riders run their tire preassure's too low for the sake of a softer ride. Many do not realize that tires are part of their suspension package and tire preassure is the main component of tire suspension. There is a formula for determining the proper inflation pressure for your ride. I have always found mine to be 2 to 4 lbs greater than factory recomended settings which I see as only guides to get you close as they can not anticipate everyone's riding weight or style. Just my 2cw:hii
 
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