When driving on a rough road with the roof on (convertible) I am experiencing a very noticeable knocking sound coming from the right side rear end. It sounds almost like a rattle but with a clear knocking type noise. Can someone on the forum please help me diagnose the root cause of this knocking? Does anyone else experience this in their XKR? One mechanic has suggested it is the rear end U joints and that both need replacement but I am not confident this is the problem. The knocking sound is clearly coming from one side. The shocks and springs are tight. I originally thought this sound came from the roof but recently I heard it with the roof down. It is just more prominent a sound with the roof on. Please help if you can.

 

Same thing happened to my wife's 2006 XK8 Victory Edition convertible during the summer of 2014 at just over 83,000 miles. It took quite awhile to figure out that the internal valve inside the right rear shock had broken off and was rattling around in there (this is a relatively common issue and it is almost always the right rear shock). The shock continued to perform normally, but the constant rattling noise drove my wife crazy whenever the convertible top was up (which was most of the time). Wayne (cjd777) and I replaced both rear shocks with new Bilstein 24-067270 shocks in October 2014 (I sourced them from fcpeuro.com). Problem solved....

 

With the best will in the world, you are never going to get an answer to that question from a forum. All you will get is a laundry list of anything at all that could make a noise, which really won't help you. You need to get it up on a ramp and investigate, or have someone do it for you and actually demonstrate the problem before you commit to any repairs.

 

Yes, I agree with bladerunner, however, here is a laundry list of things to check:

I would look into the suspension bushes. Could be anti-roll bar bushes, lower shock bush, anti-roll bar links. On the front there are more bushes that could produce a similar noise. Are you certain the noise is coming from the rear?

The u-joints would cause:

• Squeaks when starting to move forwards or backwards
• clunk when shifting from drive to reverse
• Vibrations felt throughout the car when moving at speed (this could be any number of other things and is not pathognomonic of a u-joint)

Sure, it's possible you have a loose brake caliper, but brake feel would also be affected. Perhaps the brake dust shield is loose; those do tend to rattle, but not clunk. Bad springs wouldn't cause a clunk unless they have shattered (highly unlikely), they sag when they are old, the car looks as if it has been lowered. I think the roof is a red-herring.

We cannot discard the possibility that you have something loose in your trunk that is banging around. Perhaps a small tool. Also, loose bolts for the control arms or wheel knuckle could cause a clunk.

 

Agreed. Thanks for your feedback. My hope with this post is that someone will have experienced the exact same symptoms as what I have tried to describe. The knocking noise is quite distinct so I think that if another owner had it they would recognize this type of sound right away. Perhaps one respondent has. Changing the shocks is not a crazy fix and is cost effective. But thank you very much for your input. I really appreciate it,

 

Thank you Jon89. I hoped that with my description someone out there on Jag Forums would immediately recognize this sound. It is really quite distinctive and if you had it previously you would know what I mean. Perhaps you have nailed it for me. Changing shocks is not a major undertaking and worth a try. My vehicle has 60,000 miles on it and it is probably time to replace them anyway. What I have a problem with is "expert mechanics" who just try stuff at owner expense without thoroughly investigating. U Joints is not a trivial repair. Thank you again for your insight Jon89.

 

Thanks jiandanielxk8. I really appreciate your comments. Its definitely not anything loose in the trunk. I'm obsessed with finding this rattle/knocking noise and have searched, pulled and shaken everything I can get my hands on to figure it out. It is for sure right rear end and I've had it on a hoist twice to see what is happening. There is something internal going on somewhere. The mechanic showed me the play in both the rear wheels (grab the wheel top and bottom and pull back and forth and you can definitely fee a little play in both of them) and determined it was the U Joints. I've had another mechanic tell me that this play in the read wheels is normal. The car is in mint condition and not a lot of miles on it (60k). The broken valve inside the right rear shock seems like a real good possibility. It's almost time for the car's annual winter hibernation so I'll investigate this again in the Spring. Thanks again for all your suggested items.

 

Lower shock bushing. They all fail and promote a knocking noise.