Pulsing noise matched by flicker in speedo needle

Hi all. I have a "wob wob wob" noise over the rear axle.

It increases as I go faster, and is still there if I stick the van in neutral.

My amateur diagnosis was a wheel bearing, and that's the opinion of Toyota - who agreed to take a quick look at the van on passing.

Only question in the back of my mind is that the frequency of the pulsing noise is matched by the speedo needle, which flickers at exactly the same rate (so it bounces up and down at slow speeds and then flickers faster and faster to the point where you barely see it move).

Seeing as the speedo sensor is attached to the gear box, this makes me wonder if the noise is actually more of a transmission issue than a wheel bearing.

Has anyone else experienced this? Any thoughts?

Thanks.

Hello.

While you write it’s seemingly related to speedo ‘flicker’, I think you need to identify whether this is related to various rotation speeds such as:

1 - wheel rotation (more likely to be bearing there), or

2 - Prop shaft rotation (poss gearbox, prop shaft or diff input).

But there are possibly others.

There are various online calculators so you can work out how fast various bits are turning at a given road speeds. A couple of examples are:

https://tiresize.com/
and
https://www.blocklayer.com/rpm-gear.aspx
, which is very good.

You might also find it useful to set a gopro to record the sound so you can match it with a metronome phone app.

Problems with wheel bearings is usually evident in play / wobble.

Good luck and

HTH