Help, Goldwing handling - frontend goes into tank slapper/speed wobble..

[Chris Ash]

Any advice/suggestions on the cause of the following would be much appreciated:

Rode my GL1200 Aspencade the other day at a steady 40 mph, took my hands off the handlebars to stretch and the bars started to wobble, quickly turning into a violent tank slapper/speed wobble, was able to regain control quickly but quite concerning. Is this heard of before with the GL1200?

A bit of background - its an 87 Aspencade, no mods that would affect handling as far as I'm aware. Ive owned this bike since June this year, done over 1,000 miles but never noticed this wobble before until the other day. Bike has been well maintained by previous owner (15 years same owner) I believe and is in good shape for the age, generally.

Tyre on the front is decent, relatively new by appearances and not unevenly worn. I lifted the front end and the bars move around smoothly and freely, bearings don't feel crunchy, stiff or worn out. Front forks are not too bad, a little spongy but still have rebound and resistance increases with the use of the compressor. Same can't be said for the back end. The rear shocks feel like they have gone, barely any rebound and rear tyre looks like its close to needing replacement. Could the rear end affect the front to the point it would cause handlebars to wobble violently?

thanks in advance for any feedback..