Anything like Chassis Ears but for finding vibrations?

[rcx106]

My Vitara 4x4 is vibey, it's been lifted, prop shaft is well over specified angles so no wonder, but also got a wonkey wheel, and I suspect that some of the custom flanges I had made may not be true.

I'm in the process of fitting a double cardan prop shaft which should sort the prop shaft angle (standard prop shaft, rule of thumb is good for 7 degrees, double cardan good for 14 degrees). I'm going to have the custom gearbox-propshaft flange tested for run out, and replace the wonkey wheel.

I've discovered "Chassis Ears" for finding noises, I'm wondering if there's anything like that for finding vibrations as well? If I have all the above done and still have vibes I'll be stuck for what else to try!

Thanks!

[russell_ram]

rcx106 said:

I've discovered "Chassis Ears" for finding noises, I'm wondering if there's anything like that for finding vibrations as well? If I have all the above done and still have vibes I'll be stuck for what else to try!

But your Chassis 'Ears' are already measuring vibration.

The signal from a croc clip mounted accelerometer is amplified so you can listen to it via some headphones. Noise/vibration are pretty much the same thing (simplistically) and at the frequencies generated by a grumbling bearing or a braodband knock from a worn joint it works enables you to home in on the problem area by listening for the loadest location.

Your issue is that the vibration you are complaining about now is low frequency - wheel first rotational order at say 30Hz, prop 1st and second order rotational force and vibration at under 100Hz. Those are too low for you to 'listen' to via the headphones.

You could try looking at the signal amplitudes from a chassis ear on a scope - the low frequency content usually dominates the overall amplitude particularly if you're only looking at a specific problem speed.

To do it properly you need a much more sophisticated data acquisition and analysis system ('NVH gear') which doesnt really exist at a 'casual' user level.

Edited by russell_ram on Wednesday 26th August 14:10

[rcx106]

Thanks Russell. This weekend I'm making a start on fitting the double cardan prop shaft, it could be that cures everything. It won't be a small job though, got to remove the transfer box, swap out the main shaft for one that's been modified to take a flange (stock one takes slip on prop shaft, new prop shaft is flange type taken from Hilux Surf), then measure up prop shaft length, and send the new prop for shortening.

After that I'll deal with the wheel.