Dear Jaguar Enthusiasts,
I started experiencing a hard knock on the front left of my 2003 XJR after my mechanics replaced the front shocks, the motor mounts and replaced bushings and ball joints of the front suspension.
The knocking sound when going over an uneven road surface with recessed manholes etc. is very loud and hard, and appears to come from a heavy component. It sounds as if the motor mount has collapsed or the shock is hitting something even though we replaced everything.
What could this be?
Any suggestions would be greatly appreciated.
Thanks
SP

 

I think there's a subframe mount too? sounds about the only thing not on your list.

 

If they replaced the rear subframe mounts the only ones available (Uro think) are too small and are loose in the housing. When going over bumps or turning the subframe moves around and bangs on the frame. I have been through this and my fix was to use loctite 638 to secure the bushings.

if it is not this then something may need tightening, perhaps the other subframe or engine mounts

 

My XJR has same symptoms....happened a few days ago when a prospective buyer was test driving the car. The outer plastic/rubber-like shell of the top donut in the URO shock mount virtually exploded and the inner material very quickly ground itself to bits. Less than 1500 miles on this part. (Nice timing....no sale). I've ordered a new set of inserts from forum member "phobman". I'm also going after Rock Auto who sold me this URO trash and contacting NHTSA to nail them for a safety issue.

 

Come winter, almost always top shock mounts. On F35063, I used a big hammer and put in neoprene rubber inserts; as soon as it got cold, they hammered going over any rough surface, later switched Mehle and Uro replacements, dead quiet. On this latest unit, replaced the originals with Uros: quiet for two years, then had to replace again. An aside: same hammering in the back; pretty sure it was shock mounts and isolators. Nope, the donuts holding the exhaust pipe in place had also hardened with age -- soaked with silicon spray, dead quiet for the last five months.

Roger, URO trash! Couldn't find Mehles; if the car (or me) lasts, have phobman on speed dial.

 

I got myself very cheap rubber parts online, modified them a bit and solved the issue on the cheap:
https://www.jaguarforums.com/forum/x...2169af-266115/

 

Dear Jaguar Enthusiasts,

Thanks for your valuable feedback. I forgot to mention that the front subframe bushings [MNA2370AA*, CCC6832*, MNC2370AB]] were replaced as well.

We'll take another look at the left front shock bushing, which compressed under load.

Best, SP

 

MNC2370AB is the bush I was referring to. Check that this bush is not moving in the subframe mount. Take a pry bar and try to move it

 

To recheck motor mounts - they leak their damping fluid, leaving a witness on the chassis leg, they also stretch their bolts giving enough room to create a loud knock over speed bumps etc, that's how they meet their demise. If they've failed, revving the engine lifts the right side of the engine up off the mount you can see this with the bonnet open.

 

If not the shock mount, it’s likely the Upper control arm bushing and or ball joint.

 

Dear Jaguar Enthusiasts,

We additionally replaced the left front lower rear control arm with the ball joint and the sway bar end links. Yesterday the hard knock seemed gone. Today it is back again. How is this possible? A temperature effect?
I am considering replacing the front left upper shock mount MNC2169BE, which seems different from the front right upper shock mount.

My mechanic observed the shock mount bushings under load (see attached pictures and videos) and found that the left side seems softer, which may explain the hard knock/clunk on the left. I has a yellow color and moves quite a bit in the video. The orange one is the one on the passenger side and it appears to move less. Both shock mounts were sold as new.

Right side

Left side


Any feedback would be appreciated.

Best, SP

 

A new upper shock and spring mount plate for the driver side solved the hard knock.

Thanks, SP