Next move will be ( drum roll )

Progressive rear mechanical side shock.
I have installed the front springs and run 20 wt. in the forks set at 7 " below the collapsed fork tube top. I have always used progressiv suspension and also have it front and rear on my 77 GL 1000 suicide shift road munster. I put it on the 1980 Interstate also.Had this one in the early 80's.

The reason for changing this on the 88 Bagger is a speed wobble in long sweepers. it seems like the stock shocks just don't have enough dampening to suit me. The bike po-gos in turns with small road humps . Also think from past experience the overall road feel and ride will improvwe greatly.

What say U

I got high speed wobble (slight) after going DD. It could be the front tire.

Mine did that because I had a broken belt in the tire.

Jerry

Mine has always done it 3 different tires , is not as bad with the Dunlop wintersport , but it is the shock dampening . Was worse before I changed the front springs and changed to higher weight oil. Only does it when there are ups and downs in the road bed. And I want a better shock system anyway.It can't hurt any to upgrade.

Check the bearings on the triple tree.

I have seen a lot of posts about the shock bushings causing the problem you are describing. Will the Progressives have new bushings? If so you get a better shock and eliminate that possibility to!