Sudden severe tankslapper. Any ideas?

[gsJack]

I had a decel wobble on the Nighthawk 650 I traded in on my 97 GS when releasing the bars at about 40 mph  and replacing an unevenly worn front tire improved it considerably but it wasn't eliminated until I replaced the steering head bearings.  Felt a notch in the center position of the bars when the front wheel was lifted.

My 97 GS went it's 80k miles with no stability problems on the original rear shock but the 02 GS had a leaking rear shock at about 30k miles and on a ride of some distance from home the shock went completely and it was almost impossible to get it back home with no rear shock resistance left. 

So besides the condition of the front tire and the rear shock check those steering head bearings too on older bikes with low mileage, the grease hardens and the bearings get notched.

[user11235813]

@Jack,

Tires are definitely good. As for the steering head, it's as smooth as silk with no play. The shop I took it to for a second opinion thought it felt fine, I thought it felt a bit loose, meaning almost no friction when turning but they said if it was too loose there'd be play and there was not.

I'm kinda feeling that it's not the rear shock (although I will be getting an R6 eventually) the reason I say that is because I just tested it again and it takes just a pretty light tap, maybe only a few newton metres to induce the wobble, no problem cornering or riding it but being this twitch makes me a bit nervous. I'm going to see if it's possible to get a video of it actually happening.

[RichDesmond]

...I'm kinda feeling that it's not the rear shock (although I will be getting an R6 eventually) the reason I say that is because I just tested it again and it takes just a pretty light tap, maybe only a few newton metres to induce the wobble, no problem cornering or riding it but being this twitch makes me a bit nervous. I'm going to see if it's possible to get a video of it actually happening.

Not sure why you feel like it only needing a light tap to start the wobble means the shock's not the problem??

Many bike have the decel wobble, generally it takes no input at all to start it. Just take your hands off the bars at 40-50mph and there it is, increasing in amplitude until you grab the bars again.

[pliskin]

I had a slapper start one time on my GS. It happened out of the blue one day when I let go of the bars during a deceleration at about 50mph. I was not on the brakes at all, the motor was braking my speed and the front end was being compressed slightly when it started. I grabbed the bars before it got out of control. It scared me and now I'm careful not to let go of the bars when slowing down/decelerating.