I’d definitely get a proper suspension inspection before agreeing to that expensive quote. A clunk over speed bumps or uneven roads can come from quite a few different places, and it’s difficult to identify the exact cause just from the noise.
On a Navigator, I’d want the garage to check the sway bar links and bushings, control arms, ball joints, shock or strut mounts, and the shocks themselves. Loose mounting hardware can sometimes make a surprisingly loud clunk as well. If the vehicle has air suspension, I’d also have the air suspension system checked rather than assuming it’s simply a worn shock.
One thing that can help is paying attention to exactly when the noise happens. If it mainly happens when one wheel goes over a bump, that can point the diagnosis in a different direction than a noise that occurs when both front wheels hit a bump together. Turning the steering wheel, braking, or accelerating while listening for changes can also give the technician useful information.
I’d be a little cautious about a Workshop that gives you a large quote without explaining what they actually found. Ask them to show you the worn or damaged component and explain why it needs replacing. If a shock is leaking, a bushing is torn, or a ball joint has excessive play, that should be reasonably straightforward to demonstrate.
If the Navigator has air suspension, it is also worth checking whether the vehicle is sitting evenly when parked. A corner that gradually drops lower than the others can indicate an air leak or another suspension-system issue. The compressor, valve block, height sensors, air lines and air struts can all play a role, so replacing one expensive component without checking the rest may not solve the problem.
I’d get a second opinion from a Garage that regularly works on larger luxury SUVs before spending the money. A proper scan combined with a physical inspection should give you a much clearer idea of what is actually causing the clunk. If everything else checks out, then you can replace the failed component with confidence rather than changing parts based on guesswork.
