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Hi all,
I'm starting to get stumped with this one so thought I'd pick the collective brains.

My car (Spit. Mk IV, AVO front shocks on uprated springs, Spax rear shocks with standard spring, Polybush'ed in most places, alloy steering rack mounts) has started to develop a nasty vibration at motorway speeds.

Initially it was around 70-75 but seems to be working it's way down so that it's now detectable from 60, becoming excessive around 70.

The vibration makes the whole car shake/judder at around 5-10Hz.

So far I've:
- Had the front wheels re-balanced (as it seemed to be coming from the front).
- Replaced the prop shaft UJ (after much farce) and fitted it with pot at the front/UJ at the rear (was in the other, wrong way around).
- Tweaked the front shock rates up/down with little noticeable difference.

I've tried to 'bounce' each corner of the car to test the shocks but that didn't get me very far - even sitting on the wing and jumping off doesn't promote much suspension deflection but what there is seems to be stopped quickly.

Any thoughts where to look next/another test to try?!?

Thanks,

Mark