I have a problem with cowl shake on my 2003 XKR convertible. It has 20,000 miles on it and it was like this when new. I also drove another XKR convertible and it had the same shake in the steering wheel when driving over bumps at speed. I have the original 20" Pirelli P Zero tires that i had balanced and checked for out of round. The tires are still good, but I am going to change them because of age. I don't think that will help. I also have a 2002 XJR with 100,000 miles on it and it drives solid as a rock. It is just a pleasure to drive. At 100,000 it is still perfect in my thinking. I would like to start driving my XKR more but would like to improve the problem. Is there a fix for this design flaw? I guess I could buy a Jaguar F-Type R, but I am hoping for a cheaper solution. My XKR is as showroom new, never been in the rain.

Thanks for any help, Ernie

 

Hi Ernie,
I recently bought a 2003 XK8 convertible with 30,000 mile.
It came with 17" wheels, that were inflated to 34psi all around. This produced the same thing you speak of. The fix was to lower pressure to 28 back, 26 front, as specified under the console lid for maximum comfort. I can't imagine you can do much with air pressure on 20" in wheels, but try lowering pressure one pound at a time.
I'm the owner of a 2011 335i also. This is interesting because the 335i has a smoother better dampened ride over choppy rippled pavement. On the other hand the Jag which I assumed would be smoother in all conditions is better over bigger bumps. The Jags lack of dampening would bother me if it didn't corner so beautifully for a big car. To summarize thought 335i would corner better than XK8, (it doesn't) and thought Jag would be a better ride, (it isn't).
I'm aware of differences in XK8 and XKR suspensions.
Finally, I would get 18" wheels and keep tire pressure's relatively low. 80% of problem solved.
gary

 

I had a persistent cowl shake when I bought the car. Went through the ENTIRE front suspension, cowl to shock tower bars, etc. etc. I finally turned out to be engine mounts. Both were degraded and broken. The only thing holding the engine down was gravity.

 

Sorry for the slow reply, been on the road. Thanks for the replies. I love the looks of my 20 inch wheel option. They are the BBS with the screws around the rim. They are the nicest rims that I have ever seen and I can't part with them. I looked at the motor mounts and all looks like new as it should as the car has always been in my garage and has few miles. However, Gary, I can make a test on the wheels by taking the 18 inch wheel off the XJR with brand new tires and put them on the XKR. They are not so low profile. I can vary the pressure and see what I get. I was hoping for some ideas with bolt on suspension parts and all would be well. I'm sad.

 

Depending on your brake setup Ernie that may be a problem.

 

Heh erniejenson,
i think the reality of these cars is that the suspension is very tight, hence the great cornering ability in the city for a biggish older car. The cowl shake on rippled pavement is unavoidable with that strut spring combo. Mine as I mentioned is at 50000km (31000miles), and all the rubber suspension parts I've touched are pristine. Don't know how that's possible on a 14 year old car. I saw mentioned in some reviews from 2003 that cowl shake was present when new as well.
When I'm on relatively smooth pavement, (anything better than nasty), or the highway, the car feels like I'm riding a magic carpet. I literally think I'm breezing along 2inches off the ground. Priceless. 3000km and 34 days into Jag adventure my wife and I are absolutely in love with it.
For what it's worth I really don't mind the look of the 17" oem's that were put on by the previous owner. I'm sure he was also a little older like me.
Finally I bet you notice a big difference if you try this 18's and keep the pressure on the low end. And just keep going lower until you like the ride cornering balance. Don't be limited by suggested pressures, keep experimenting. For instance, couldn't believe the difference between 28-26 and 27-25 where I am currently. Now if I went for a highway drive I would definitely bump them up a bit. Phew.. I could go on all night.

 

One final thing Ernie, as a point of reference since I've changed my pressures I no longer have any cowl shake on bridge expansion joints, just a satisfying thunk, loud but smoooth. This was the point I knew I had it right.

 

I think l have read all the posts but may have missed it, but it needs to be noted in the comparison between the two cars mentioned ( XKR & XJR) only one of these is a convertible.
That's comparing apples to oranges as far as rigidity is concerned. Certainly not just wheel size difference nor is it a design flaw.

 

Also, perhaps have the wheels checked to see whether there is any warp in them. From my on experience, these aluminium wheels can warp slightly with use, and it is something that can easily corrected by a specialist wheel refurbishment company

 

Tried putting the XJR 18" on the XKR instead of the 20"s. Won't fit. I reduced the pressure to 27 psi. from 34 psi. That made a big difference. The 20" wheels are really big and heavy. That is a lot of unsprung weight. I thing the issue is not enough beef in the suspension to handle the weight. My friend, new ZO6 has a lot more beef in the front end. I just wonder if it is body flex on suspension weakness. I am not too happy with the low pressure but it sure makes driving more pleasurable. Thanks for the advice. I guess I will just have to cut my pressure until I get something that I can live with.

 

I've never seen a convertible without some cowl shake.

 

My SLK convertible has no cowl shake. It's actually feels more solid with the top down.

The XK8 was a surprise to me with the amount of cowl shake it has. I have done most everything I could think of to tighten it up to no avail. Just not enough chassis stiffening from the factory in this car. As mentioned before, on smooth surfaces or the highway, the ride is fantastic. In my neighborhood, the streets are an absolute disaster and it is not pleasant driving the XK8 here. You can see the windshield frame shake.

With the top up, the cowl shake is almost nonexistent which tells me the problem is how stiff the chassis is or isn't.

 

It's hard to believe a soft top of any type would contribute anything to the stiffness of a chassis.
Have you checked the condition of the various crossbraces built into the car?

 

New bushings if needed, 17" wheels, comfort psi (28r, 26f),
cowl shake 98% gone. It's clear to me that with the long overhangs, very stiff springs, very old chassis design and being a convertible with in many cases aging rubber bits that there has to be cowl shake. IMHO this car has a very good ride with brilliant handling with 17" wheels and 28,26 psi. Bigger wheels may look a little better but not worth the twitchy harsh ride over rippled pavement for people expecting a luxury ride as week as sweet cornering, IMHO.
Gary
2003 XK8 'vert
2011 335xi sedan

 

Correction; " as well as sweet cornering"