Calling on the collective wisdom here, as a novice mechanic almost at my wits end.

For the past four years I’ve had an intermittent heavy knock from somewhere under the vehicle. I’ve been underneath - often! - wobbling, prying and yanking bits, to no avail. The exhaust has been rehung, the perished front steering box ball joint replaced as possible causes have been identified. It’s had a new clutch and the flywheel seemed fine. Regularly serviced. And two different LR specialists plus two local garages have driven it and poked at it while it has been in for other work and servicing, but haven’t found the problem. But it is getting worse - as in, more frequent.

It’s quite a heavy sounding knock; it happens at any speed - fast or slow - over lumps and bumps and other minor undulations in the road and sometimes when cornering at slow speed (e.g. pulling out at the end of our road); it happens when I’m on the accelerator (steady or accelerating) - but it’s definitely NOT the occasional clonk from the back end when taking up drive (it does that too sometimes); it’s not obviously connected to clutch / gear changes; I can’t make it knock by jumping up and down in/on it stationary (which makes me think it’s not suspension); I haven’t been able to find play in any bushes; and I don’t think it happens when the vehicle is rolling along in neutral.

Which makes me think it might be axle / diff / shaft / gearbox related. At a guess, it’s coming from the front end - feels like maybe to the left of my feet when I’m driving along.

Any thoughts? It is definitely getting more frequent and I really need it not to fail on a long journey. It’s really taking the edge off enjoying a Land Rover that I dearly love.

Failing bush in a shock absorber, bent shock, broken or soft gearbox/ engine mount, centre tunnel just touching gearbox, the list goes on, get underneath and start looking , anything shiny ( rubbing) that shouldn’t be?

.

Are you 'friendly' with an MOT garage ?
They have 'wobble' tables (play detectors) on the ramps, that can help identify if it is suspension/steering related.

If you can remove the front propshaft you can drive the car around and then repeat with just the rear propshaft off to check the UJ's

Don't know anything about the Fender but after changing every ball joint on my L322 it turned out to be an ARB bush.

A frame ball joint.

Al2O3 said:

A frame ball joint.

Click to expand...

^^^^this.

Al2O3 said:

A frame ball joint.

Click to expand...

Thanks.

How do I check this? Just a case of inspecting it and putting some force around it with a big screwdriver?

To be honest, I’d dismissed this as a possibility. Partly because it doesn’t knock when I rock and bounce it when stationary, and partly because it sounds like the noise is further forwards. But will take another look.

miktdish said:

Are you 'friendly' with an MOT garage ?
They have 'wobble' tables (play detectors) on the ramps, that can help identify if it is suspension/steering related.

If you can remove the front propshaft you can drive the car around and then repeat with just the rear propshaft off to check the UJ's

Click to expand...

Thanks. I’ll see if my local MOT place will wobble it for me.

freelance said:

Failing bush in a shock absorber, bent shock, broken or soft gearbox/ engine mount, centre tunnel just touching gearbox, the list goes on, get underneath and start looking , anything shiny ( rubbing) that shouldn’t be?

Click to expand...

I’ve had a really good look for shiny bits but will look again. I hadn’t explored the gearbox/tunnel possibility so will take a better look at that. Thanks so much for the suggestions!

Gruber said:

Thanks.

How do I check this? Just a case of inspecting it and putting some force around it with a big screwdriver?

To be honest, I’d dismissed this as a possibility. Partly because it doesn’t knock when I rock and bounce it when stationary, and partly because it sounds like the noise is further forwards. But will take another look.

Click to expand...

Not easy. I would jack it up and support it on the chassis rails, so the rear axle is hanging. Take the wheels off. Put a trolley jack under the diff, inline with the axle. Jack it up a bit to take the weight off the shockers and detach either the top or bottom shocker bolts and release the shockers.

I'd then see if I could rock the axle and A frame side to side on the trolley jack.
I'd be looking at the condition of the A frame ball joint and the two bushes at the end of the link bar (number 3 on this diagram)
The bushes are obviously further forward than the joint, one of them may be the cause of your noise as could be the joint transmitting the clunk through the link bars.
If you've ruled everything else out it's certainly a possibility at that age. The not doing it while rolling along in neutral is making me go hmmmm?

@Gruber just thinking. Obviously, the A frame ball joint is designed to move, but with a lot of effort you might be able to see 'unatural' movement. It'll be worth checking your trailing arm and radius arm bushes too. I know you said you've been bouncing it from inside and out, but it's difficult to replicate a rolling, bouncing Defender because they're so much heavier than a standard car. Freelance's shocker bush is also a good shout, though the not happening when freewheeling puts a hmmm? on that. Power on/off, even very lightly, is going to affect bushes and joints.