Oh gosh, again the front suspension is making a knocking sound - I've replaced many of the wear parts already, so the sleuthing is marginally easier now, lol

What would cause a distinct "knocking" sound when you go over bumps, especially while turning? The knocking can also be easily replicated by simply rotating the wheel rapidly back and forth at any speed (i.e. in a parking lot.)

The following parts are new, were installed just a few months ago, although potentially not installed correctly:
Shock Absorbers
Upper Shock Mounts
Outer Tie Rod Ends
Stabilizer Bar Links

The rubber on the following parts have dry-rotted/failed and will be replaced at my next mechanics visit:
both engine mounts
transmission mount

The following are 2002-original rubber bits that may need replacement:
Stabilizer Bar Bushings
Control Arm Bushings (all 4)
lower shock mounts

 

add wheel bearings to it. Confused a little on lower shock mounts, though. There really isn't anything for lowers, since the bushing is pre-installed for the front shocks. So there's not really anything "replaceable" as a lower mount, unless the bushing in the new shocks are already bad. Control arm bushings can certainly do it though, too.

 

Could Control Arm Bushings make a knocking noise over bumps if they're worn? That's a likely candidate if so

Worn Wheel bearings sound very different, they're okay afaik

 

From what i can read here, its most likely the short link that connects the antirollbar to the lower suspension arm. In Sweden we call them, not without reason, -drumsticks. :-)

 

Can you feel it in the steering wheel? Then have fun!

The rear front subframe bushes will be your culprits... Entire front axle out, press out the bushes, press in some new bushes, reinstall again.

Been there, done it, got to do it sometime to my car...

 

I see engine mounts in your future - they knock when goosed, and can sound very much like suspension.

 

Do agree they sound different, more of a rattle than a "clunk" when they've gotten that bad, but the humming would start rather soon after that started. Only stating it if it hasn't been, but I know I had a rattle that disappeared once I fixed mine this week, so was just adding it to the "it could make a sound" list.

 

Can't feel it in the steering, actually handles great, it's just an annoying/disturbing noise.

The engine mounts aren't working much at all, engine props up under load a good 4"/10cm - but the noise is irrelevant to engine load, happens even while idling over bumps.

Einhead, do you mean the Stabilizer Bar Links? If so, those are new.

 

You can actually check the subframe bushes by simply pressing the brake pedal and have someone rock you back and forth. The subframe will move more, if they are worn making it go "clonk" or "knock" when you do this. Engine off of course.

 

And there's your answer - your engine should not budge. Description to a Tee.
I replaced almost all the front end bushes on an XJR and still this clonk persisted.... I approached the dip at the end of the road and clonk....(my then girlfriend) laughed...didn't see much of her after that....

Anyway a picture of the common problem that is the XJ308 engine mounts, 2 issues, they burst and loose the damping fluid, then stretch the bolts until one breaks. In the picture the top bolt had stretched and the bottom snapped, you can see were it's hammered the subframe.

Also, you don't need to fully pull the engine if the lower front subframe mounts are done, just supported while lowering the back of the sub. Cut the old ones out, tap the new ones in.

 

Couldn't I do this solo/myself by just using the parking brake? The rocking you are suggesting is forward/back, not side-to-side, right?

 

Nope. The parking brake works on the rear wheels. You want to lock the fronts though.

 

For anyone with the same issue, I've had the Stabilizer Bar Bushings, transmission mount and both engine mounts replaced and the clunk is finally gone! So the bar bushings are the most likely cause, but it could have been caused by the engine mounts too.

At this point the only original rubber in my suspension are the 8 Control Arm Bushings that the mechanic said appear totally fine and are not necessary to replace - everything else has been swapped for new in the last year.