Peculiar issue - bouncy Jimny

My Jimny exhibits a rather peculiar issue. It bounces slightly on perfectly smooth road surfaces.
At first I thought it was my imagination, but I confirmed it by some tests.

The bouncing is most noticeable at relatively slow speeds of around 30 km/h. The entire vehicle bounces repeatedly and rythmically like constantly going over very minor speed bumps, one wheel (not one axle) at the time. This is even when coasting (gearbox in neutral).
Another way to describe the phenommenon would be like if the tyres were slightly eliptical or if they had small edges (like if being an octagon instead of a cricle).

I had removed the rear panhard rod from the vehicle about a thousand kilometers ago, but I returned it properly and tightened the bolts with a torque wrench to the correct torque. Apart from that, no other suspension component of the car has ever been touched since it had left the factory.

The vehicle is 8 years old with 95 000 km on the odometer, and it has not left asphalt for the first 90 000 kms. No collision ever. So I do not expect worn bushes or bent metal.
I regularly check my tyre pressures and I have good quality Goodyear Wrangler AT/SA+ tyres. I personally rotate my wheels and clean the hubs when doing that, all with a torque wrench of course.


Any ideas?

If you have not done so already it may be worth checking each tyre for deformities. Jack the wheel clear of the ground and spin each, check the tyre is round and no lateral movement of the tread pattern. I have seen a tyre that had lateral movement, causing a shake on the steering. It looked ok and was balanced, but needed to be replaced.
Also check your dampers are ok. Remove the bottom bolt on each and make sure the gas pressure extends and they can be compressed. I have just replaced the rears on mine, even though I believed them to be good, one had no damping function at all.
Also check the Universal joints on the prop shaft for any play and the engine / gearbox mounts are good.

- Just thinking of things that rotate or control vibration.

Mike

Most suspension manufacturers would suggest replacement after 50k, that is to maintain peak performance. My car had 75k (miles) and was very tired, much better when replaced....

sniper

Sounds like dampers to me, You can do a simple bounce test on each corner. Park the car up, put the hand brake on - one corner at a time, push the corner of the body down as hard as you can and quickly release. The corner you've pushed should bounce 1-1.5 times and then return to centre. If it just keeps on bouncing and swaying the dampers aren't damping the spring.

Very Crude test - but effective. I agree with all the above methods and comments too. Dis-connecting the lower damper mount and compressing fully and releasing will be a more accurate test. If the Damper stays compressed, dast ist kaput!!

50k miles is standard life out of any OE dampers.

Suspension bushings and ball joints could well be worn as well, but this won't contribute to the bouncing. You'll eventually just get vagueness in the steering, pulling to the left/right at high speeds and knocking if they're really bad... A quick visual with a torch will suffice. Any cracking/perishing replace them.

Yes I'd say dampers too.

I know it's a different animal, but Ive got those horrid old Armstrong lever arm shocks on a sportscar - once they get worn or low on oil, the car feels almost as if its 'floating' and vague - and I guess bouncy too, as you have described