fj75 intermittent vibration (1 Viewer)

[FJ75 Bigbird]

Hi I'm new to this but some thoughts would be greatly appreciated, My old 1985 FJ75 3F troopy has a weird thing going on and it's been going on for a very long time, because it goes away for months and months and then inexplicably it's back. a serious vibration can be felt from low speeds and becomes violent at about 60-70KPH but not in the steering it's through the whole chassis.
Running 5 year old BF Goodrich 31/50/15 MT, 2" lift new shocks and leaf springs
I've driven all the way from southern Tassie to Sydney and back again and not have it happen even towing a large load on the way back. it happens for a day or two then goes away for months.... then out of nowhere it's back.
got me stuffed any ideas?

 

[coldtaco]

those kind of problems suck :-( if you haven't already done this maybe next time it happens give the drive train a good once over, check anything and everything you can. how are the leaf spring bushings?

 

[FJ75 Bigbird]

Hey Thanks for the reply Coldtaco, all the bushes and suspension components are only 5 years old. just so weird that the vibration completely vanishes for so many months at a time.

 

[roscoFJ73]

Sounds like a death wobble from a bad castor angle. Sometimes my FJ73 would get a wobble weeks apart. To diagnose it, the suspension shop made the castor a lot worse, then brought it back to a point where it never reappeared.
Mine was always worse towing a trailer. But sometimes just coasting downhill would bring it out.