Hello all,

First of all a big thank you to everyone contributing to this site. Since I bought my 1999 Jaguar XKR coupé in March 2014 it has been the most valuable source of information!

Like many of you before me, I have a persistant knocking sound coming from the rear of the car. It is a dull knocking sound that manifests only when you drive uneven roads or through potholes. My car has CATS. This is what I have done so far:

• Replaced upper and lower rear shock bushes
• Replaced all sway bar bushes
• Replaced A-frame bushes
• Replaced monostrut bushes
• Fixed the rattle in the rear brakes
• Checked all heat shielding underneath the car
• Checked the exhaust silencers and rubber mountings
• Greased and lubed every part of the trunk lid
• Checked if the third break light is fixed
• Took out everything from the trunk. Then lied in there my selves with the trunk lid closed and have my buddy drive me around over a rocky road. Result: no noise inside the trunk, only from underneath. Oh and some very surprised looks from people when you try get our of there again....:-)
• Put a cloth between the gas door lid
• Checked if the centre caps are fixed

All to no avail unfortunately.... I read somewhere on the forum that the 1999 cars' original shocks may suffer from a sort of noise/internal problem. Anyone know whether this would sound like a dull knocking (indeed kinda like when you tap the gas door by hand)?

Basically I'm trying to see what other options are still there before replacing those quite expensive rear shocks. Maybe U-joints, Pivot bearings?

When we replaced the shock bushings there was nothing which indicated the shocks were worn. We haven't been able to recreate the knocking in any way except when driving it on bumpy roads. No bouncing/pushing/pulling the car or any part of the suspension will result in any sound at all, not when the car is standing on its own wheels nor when it is on a hoist.

The car is aligned, wheels are balanced and she handles and drives like a dream. If I could just get rid of that nasty rear end knocking noise....:-)

Your response and expertise is highly appreciated.

Kind regards from a cold and windy Holland!

Marc

 

I have this also. My shop did not see anything. He said it could be something inside the shock is broke. I have not tried to fix it yet as it is not that bothersome.

 

Brgjag is probably right - I had the same knock on both my XK8 and XJ8. It was cured by replacing the rear shocks. (Easy and cheap on my cars because they were standard non electronic units).

Just to check - the sound is like a short length of wood moving about on a bare boot floor. It happens at lowish speeds and poor roads.

It's caused by the shocks failing internally and 'bending' as they work.

 

Dear Tim, Jim,

Thanks for the replies. The sound description is accurate. It happens on poor roads indeed but even small imperfections trigger it. I hear it also at reasonable speeds.

Do the shocks 'bend' only when the car moves on poor roads? I mean is the reason why I can't reproduce the knocking by bouncing the rear of the car up and down myself when it is standing still because that does not put enough 'stress' on the shock?

Br,
Marc

 

mine makes the noise on simple bumps.

 

You'd have to be a big bloke to replicate the noise I suspect. The shocks are not vertically mounted so they try to kink in the middle rather than shorten under compression (if you see what I mean!). This leads to slackness - and the knock.
The obvious thing is to replace the shocks but the electronic ones are VERY expensive. I'm not sure what would happen if you fitted ordinary shocks and left the electronics disconnected. Anyone know?

 

My car had a bad left rear Shock that made that noise. Both (CATS) Shocks were replaced under the New Car Warranty in effect at the time.

 

You can replace with XK8 shocks, but have to do all four and unplug the module to avoid error code.

 

Check the inner brake pad. The spring on the back, which mounts it in the piston, falls off and they then rattle on rough roads. Particularly at low speed.

 

Smoggy's post has reminded me ......... on my XK8 I had a problem with a 'clunk' on throttle take-up. I thought it was the diff but it turned out to be the problem Smoggy's referring to - loose handbrake shoe. It's worth a look (but changing the dampers fixed the thunk from the boot!)

 

I agree hand brake shoes can rattle but I was refering to the disc brake inner pad.

 

Gents,

Thanks to all! Really helpful explanations. The handbrake shoe was fixed earlier but the inner brake pad spring could still be an option (although the noise is more like thunk/clunk/knock than rattle).

Regarding the shocks.... might take me a little longer to replace them considering the impact it has budget wise :-)

To Paul: The New Car Warranty, is that a US warranty program or world wide Jaguar? Certainly worthwhile to give the dealer a call so thanks for the suggestion!

Best regards,
Marc

 

Have you checked the exhaust
system?

Gus
www.jagrepair.com

 

I bought my car in 2003 w/15k miles. It came with the (transfered) new car warranty as well as a Jaguar Select Extended Warranty. The Rear Differential (Whine) and both rear Shocks (1 clunked) were completely covered under the New Car Warranty. I don't know whether Europe warranties were the same. Both Warranties are long since expired.

 

Hi Gus,

Yes we did check the exhaust system and replaced the rubber mounts of the silencers. Whatever we tried by pushing/pulling all parts of it, no noise whatsoever.

Thanks,
Marc

 

It will be the shocks Marc.

Mine does exactly the same thing.

At full noise and under load they are quiet.

Tootling along at low speed , they are noisy.

Just budgeting now for replacement of all four of my CAT type.

The OE ones cost a packet.

I am going down the path of having my local Bilstein rep rebuild mine.

I think the OE were about $1600 Aus/ pair.

The rebuild cost is $ 550 / pair

Look up Bilstein in your country or refer to a good suspension place

Pete

 

Any way to get a recording so we can hear what you are hearing?

 

I read somewhere in here that the rear shocks have some valve that shears off on the inside of the shock and somehow can 'rattle' and make noise.


that might be why the problem is solved for the ones that replaced the shocks.


just an idea.

 

Gents,

Tried to make some sound recordings today as I thought that to be an excellent idea of Gus. Unfortunately both the audio and video recording features of my iPhone do not result in an audible reproduction of the low frequency rhythmic piece of log rumbling about in the back...;-). You hear the supercharger and a lot of other stuff but not the low mhz knocking, even at full volume.

@Peter: I had the front shocks replaced last year, cost me around 500 Euro. So yeah that's not making me laugh. Might be worthwhile to see if rebuilding is an option indeed.

What puzzles me a bit is how the shocks still feel like they work perfectly yet make all this noise anyway. I had them tested on a specific test bench at a local specialist and the guys said they were fine. To me it sounds at least like something is wrong inside....

Thanks again guys for all you input and ideas!
Marc