Hi all. I recently bought my first Jag, a Daimler XJ8 4.0 LWB from 1998 – and I love it. It has done 122.000 km and is in pristine condition. However the car has a vibration which seems to be getting worse.
The vibration is sort of a vibration with some shuddering included.. It starts at about 68 mph (110 kph) and continues to be present at all speeds above that (I have not exceeded 100 mph yet – but the vibration does not seem to worsen with increasing speed. The vibration notably worsen under acceleration, light or hard makes little difference. When lifting of the accelerator the vibration reduces again. So to be clear there is a vibration at over 68 mph which worsen when accelerating but not increasingly. I cannot pin point whether its from the front or rear. There is no more vibration in the steering wheel than in the rest of the car. I have had both my summer wheels (new Pirellis) and the winter set (new Bridgestones) balanced and tested on the car with absolutely no difference to the vibration.
I have the feeling that not only does it vibrate, it sort of shudders as well. This is not a consistent feeling, more like the car is doing “ovals” – this however only occurs under acceleration over 68 mph….
Doing +68 mph and selecting “4” on the J-gate does not change anything. However the problem seems to be present at above 2000 rpms doing less than 68 when manually selecting a lower gear (like 2nd or 3rd), but not nearly as bad.
The engine rews freely with absolutely no hesitation with the gearbox in Neutral. The gearbox also shifts silky smooth at any speed, performs kickdown without hesitation and the car really goes! After driving a long time in a queue it wants to rew quite high before shifting the first couple of miles, but then it settles back in to its normal shifting pattern. Lately it has been slow to shift up from 1st and 2nd under normal driving conditions (it that some sort of adaptive program?).
I have changed spark plugs, used an additive in the fuel, used some Würth Valve cleaning spray – with no change at all. The car does about 8 km/l which I think is acceptable and the old plugs were grey and seemed fine.
The only other symptoms I can describe is the fan making notable vibration when the car is idling and the fan starts, the vibration can be felt in the car, but not something most people would notice.
When driving very slow and “dabbing” the accelerator it makes a slight “clonk” noice somewhere, but only at very low speed and a very abrupt dap to the pedal lifting of immediately.
There is no noice from timing chains and no other weird noices.
No clonking anywhere when going over bumps
No vibration and drifting to any side under braking
No fault codes from the ODBII reader – although my Delphi tester can only access eODB on the car…

Any clues to what might be wrong?
Thanks

 

I'd suspect a slightly bent wheel. You say you have 2 sets of "wheels" and mention 2 sets of tires, but I can't tell if you're saying you mount these summer and winter "tires" to the same wheels. Sorry if I'm misunderstanding your statement. But if you're mounting these 2 different sets of tires to the same wheels, then the wheels are a common denominator. I wouldn't think two different sets of wheels with 2 different sets of tires would seem likely to net you the same wobble/vibration at the same speed as you describe. So if it's the same set of wheels, if I were you, I'd take my best guess at which corner it seems to be coming from, and swap my spare to that corner and take it up to 68mph to test it. Still wobbling? Keep moving it around to the other corners. If it's a wheel, you'll find it. Maybe you'll get lucky and nail it first try. If that strategy doesn't work, then at least you have eliminated the wheel/tire possibility.

I had a untrue rim on my 98 XJ8 for a while causing a vibration around 65 mph, and quite by accident after a flat, swapped my full-size spare in and the wobble disappeared. All of my wheels and tires had been balanced at the same time by the same shop a year or two before, and I suspect that the problem wheel got a "close enough" from them, but I'll never know. At the time, I worked just a short distance from home and rarely got the car up to those speeds, so it became a "back burner" issue that took me a while to get around to. So the flat became the silver lining in my case. At any rate, that full-size wheel is now my full-time spare and I marked it as "bent" on the inside so I'll always know.

Just my .02...

 

Hi and thanks
Its wo sets of tires and rims. They have both been balanced by the same shop.
I'm fairly certain that the problem originates from either the engine or gearbox because of the way the vibration worsen immediately upon accelerating.
Today I was out looking for a convertible and tried an Audi S4 4.2. This car had a similar although not as obvious shuddering at around the same speed. Later I googled it and found out it has the exact same ZF gearbox as the Jag. It seems that this shudder CAN be caused by the torque converter not locking up, causing it to sort of letting go and re-engage in a "pulsating" way. Now i'm not sure that this is the problem as all the posts I can find related to this issue describe cars where this shudder only happens at a certain rpm and then goes away - mine starts shuddering at 68 and keeps doing it as long as dare rew/speed on the motorway..

Also the last week or so the gearbox has started to rew higher before shifting (like it was in sport mode). Its weird because even if I let it rev up tp say 3000 rpm in 1st and keep the rpm there, it still does not shift - I need to go to almost 4000 before it shifts - and then from the next standstill its back to normal. Its like it engage sport mode on its own will from time to time.

 

Okay. Gotta start somewhere, thought I'd take a poke. I'm sure other kind souls'll chime in.

 

I think you should first check the fluid level in the transmission to be sure that it is OK. That can cause shifting symptoms like your low speed shifts. I doubt low fluid would case the high speed vibration issues, but if the transmission is getting hot, you never know....

One possibility re the vibration is the torque converter lock up clutch. It engages at @ 100 kph in 5th and also in 4th at @ 80 kph. In mine it caused a vibration as you describe. There is a post on a range rover forum that describes the symptoms pretty well. If you google range rover 5hp-24, you may find it (I think the author goes by the name of "Range Rover Phil" & is in the UK). Otherwise I can try to see if I can find the link.

What happens when you accelerate to 120+ and then when you have the vibration put the car in neutral & let it coast? That should help eliminate the torque converter clutch.

Also, I can't remember if it is possible to keep torque converter lock up from happening by keeping the shifter in 3rd, but that is also worth a try

 

I would also suspect a tire/ wheel issue. Sometimes the tread can start to separate from the tire carcass and cause strange results. This was more common with old steel belted
radial tires. Engine/drive train issues are usually more RPM/Load related not something
at a particular vehicle speed. I would take it to a tire shop and ask them to road test it for you.

 

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Having them simply "balanced" is not good enough for our cars, they are very sensitive to any issues with wheels and tires.

You can "balance" a football, but it won't ride smooth.

Get a Hunter Road Force Balance job done by a reputable shop with an experienced technician doing the work. Make sure they do all the things the Hunter machine will do like breaking the beads, checking the runout on the wheels, and tires, rotating the tires on the wheels to minimize the road force and properly placing the wheel weights exactly where the machine tells them to.

This simple, relatively cheap procedure has fixed or identified lots of issues with members cars in the past after they spent a lot of money chasing ghosts because they had ruled out wheel and tire issues because "I had my tires balanced and that was not the problem."

Do this first, then look for other problems.

I suspect you have one or more bent wheels or bad tires. Regular balancing will usually not reveal these conditions.

I give this same answer to a lot of threads about vibration issues and it usually turns out that the issue is wheel/tire related. But you have to have the job done by a good shop with the correct equipment by a very experienced tech who is willing to do ALL THE WORK and do it within specification.

You should get a printed read out of the work done and how much road force each tire had and how much weight had to be added to "balance" the tires.

If you get any less then you got a run of the mill "balance" job meant for Grandpa's Crown Vic, not your Jag.

Vector

 

Vibration over 68 mph can be caused by two things.
1. bad rear tire or wheel as stated above
2. bent drive shaft

 

Or maybe the jurid coupling, driveshaft center bearing mount, transmission mount, half shaft universals. Lots of places to look, most of which require getting it on a lift.

 

While wheel balance and bent wheel are the common problems with vibration F1wannaB keeps describing transmission issues also. Certainly, 1st gear not up shifting past 3000 rpms is a problem. Maybe two problems but we know for sure there is a transmission/transmission control issue.