I've noticed lately that while driving, I seem to be getting a more then normal floating from the rear end. I notice it more when crossing a long bridge where there are surface sections and as you cross these section you can hear the clicking of the tire as they ride over the seams. I know most of you have hear this. Sort of like before there were newer tracks for a train. (Most are seamless now, being welded together) Clickidy clack, clickidy clack. Back to the story..........
The floating (up and down motion of the rear end) never gets to the point where I have to slow down, but it seems more pronounced then it has been.

Any idea's?

 

My money is on defective shocks or tires. Rotate the tires, back to front, and see if that changes the symptoms.
Pray it's the tires as otherwise you are in for getting your bank account Hoovered up.
There is a condition with tires called "trammeling" whereas the tire tread disagrees with the road surface and a vibration sets in that gets the suspension to doing weird things.

 

how many miles on the car?

 

It's the tires.

 

ross-----

It just turned 69K........

Cheers

 

Tarhealcracker and Zazzy------------

If you will, please explain how in the heck can tires cause a floating (up and down) of the rear end. Bad shocks maybe. But unless the tire's are square, I can see no reason why they could cause suck an action.........

Cheers

 

I used to drive over a metal bridge daily. Some tire treads will follow the metal patterns and it'll feel like it's floating as you drive over the metal. I changed tires and brands, 3 times, and each tread pattern feels different. Older tires will follow the metal pattern more and some treads, even if brand new, will follow it so much that it'll freak you out (and you won't want to drive over metal bridges).

 

I know the feeling when on a metal bridge, but that is a left to right pulling effect and does not cause the rear end to float up and down.
This feeling is as if you were driving a car without air ride with just the standard springs and shocks and the shocks were bad. I think the CATS system is designed to keep this in check and allow for a smooth--non-bouncy ride. I did a hard reset and think I have corrected the fault, but will have to go over that long bridge again to verify.
Thanks for your input.

Cheers

 

Relative to the tires causing your problem, it may be that tires are a long shot but a simple rotation is a cheep and quick way to eliminate them as a possibility. Just trying to be helpful old boy.


It used to be that "out of round" tires were common, not so much any more. Never the less , out of round tires do get out from time to time now a days. I recall that tire dealers used to sell ultra cheep tires that sometimes required shaving, at extra cost, to provide an acceptable ride. An out of round tire can cause all kinds of odd behavior.


Back in the day, a past CEO of Jag discontinued Donlop as an OEM supplier pending their learning to build a round tire. His actual words.

 

My car came with a set of Carrera tires. These have to be the hardest rubber used.
They float, jump on expansion strips, hydroplane on morning dew, and react strongly to irregular pavement. I plan on replacing even though they great thread remaining.

 

I would have thought it more likely a dampers problem than tyres.

I don't know how easy access is to the top of the rear air struts, but if you can temporarily disconnect the CATS connector at the top (both sides) then the dampers in the struts will default to the hard setting.Then, if you don't mind driving with a standing alarm message, you could then try driving across the bridge and see if there's any difference ... maybe.

 

Tarhealcracker------

Didn't mean to be harsh Pal, but tires causing my floating problem just doesn't seem to be the answer---or didn't. I'll do the rotate and see what happens.

Back in the day when money was REAL tight, I too used the shaving method on the used tires I had to buy--also the tread cutting machine for more tread. Don't know how safe either was, but it worked at the time. I had a 35 FORD and later a 39 Plymouth coupe, so speed really wasn't a factor. How simple those days of car ownership was.................

Thanks for your help.

Cheers

 

Chuck,
Be sure to let us know how this shakes out. Some of us really get invested in certain threads. For me its ride and handling issues.

 

TARHEALCRACKER and others.
Well I found the cause of my "Floating".

Yesterday, I was at the local Boot Store to pick up some boots I had new heels put on (yes I'm from TEXAS originally and I wear boots--always have, except in the service they were somewhat different ;-)) ).

When I came out of the store I noticed the rear end of the car was sitting lower then it normally does, not by much, but lower. I have always been able to lay my hand on top of the tires with my fingers flat across the tires back there, but when I checked, I had to bind my hand down some to reach across the tread.--not normal!

Both sides were the same. In other words the air rides were only particaly (sp?) full of air. I quickly checked the front and they were as designed and had the car--in front-- where it should be. The rear air-rides were just not full, although looking at the car, one would have thought it was fine, but my old eagle eye saw something different.

Today when I cranked her up, I felt the rear end rise slightly, so got out to do my "hand check" (you can use the method if you like, it isn't patented) and it was back where it should be. I didn't do a thing to the car, because it's been raining on and off and I was waiting for things to dry out. The only thing I did that was different is when I left the boot store, I missed what looked like the exit and drove off a small road shoulder and the small drop could have made the correction for me.

I always thought the air system (front and back) were connected as one and the four air-rides were filled as one. Am I wrong in this assumption, or are the two systems (front to back) separate? Having to replace one of the air-rides because of a failure, I know that the air system will default to a bad unit and keep trying to fill that one while the other three are full. I know also that there is just one pump, so why the air-rides didn't fill completely has me at a loss----not uncommon for me----.

Anyway, I took a slight detour tonight and drove over that long new bridge I mentioned in my first post and the Jag was rock solid as it always was. Not a hint of a float up or down. Like a sled.

Any answers to my bewilderment would be appreciated.

Cheers.

 

Weird. That the back suspension was low sounds like the Air Suspension Module 'took a vacation' for a while. Looking at the wiring diagram the ASM also controls the CATS setting of the dampers, which is a bit odd as the dampers have to be energised to be in the soft state; if the ASM were dead I would expect the dampers to go to the de-energised (hard) state.

Did you disconnect the battery at any time shortly before it came back to normal ? That could have reset the ASM if it was 'hung-up' in some way.

Can you read your DTCs (fault codes) ? There may be something there that might give an insight.

 

Cat----
No DTC codes.

I would have thought that because of the situation, there would have been at least some DTC codes, but nothing.
The only time I disconnected the btry was right after I noticed the floating--now 11 days ago. When it returned to normal was about 9 days ago.
So maybe just another Jaguar mystery that may never be solved, so, the Air Suspension Module taking a vacation sounds good to me. If you come up with another possibility, let me know. Off hand, do you know where the ASM is located?

Cheers

 

The ASM is behind the rear seat back. The whole seat needs to be removed to access it.

 

The Book says:
"The air suspension module (ASM) is accessed from the right-hand side of the vehicle, behind the back of the rear seat. The ASM can be recognized by the 4 individually colored connectors (gold, grey, yellow and pink) and the 'WABCO' logo on the front of the module. ASM calibration is required when either a replacement module is fitted, or if any height sensors have been removed/refitted or replaced."

 

Well I repalced the TriStar Carrera;s today with Pirelli's and just driving home from Discount Tire the floating and loose feel is gone. So at least in my vehicle the tires were the culprit.
The 100.00 chinese high performance tires were an easy target. The wet traction was terrible. Even with good tread remaining. The guys at discount were scratching their heads after removal. Said they were the worst constructed tire they have seen. But the worn out A arm bushings, sway bar links, and front and rear tie rod ends the car had when purchased may have contributed to the visible wear pattern.