XJ XJ6 / XJR6 ( X300 ) 1995-1997

Unstable at high speed

 
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Old 06-11-2017, 08:49 AM
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Default Unstable at high speed

The car feels Ok at around 60mph. Nice and stable more or less, but when I once in a while push it upwards to 100mph it feels just dangerous.

Normally at these speeds you just slightly correct and adjust the steering wheel but with the jag nothing really happens until you've corrected too much and it pulls away and scares you. I was afraid I had too much play in the steering racket so I bought this nylon kit but I realised it was too tight to fit these spacers in there.

I know one of the upper ball joints is due for a change though. Could this be the culprit? Should I also change the upper bearings/bushings as well?
 
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Old 06-11-2017, 09:36 AM
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A worn ball joint could be the cause, yes. But *any* significantly worn steering or suspension parts could be equally guilty.

How many miles on the car? Besides a particularly worn ball joint you might have the 'stack-up' effect of worn parts in general.

Or....incorrect alignment settings, caster in particular, can create a loose or vague feeling to the steering.

Cheers
DD
 
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Old 06-11-2017, 05:17 PM
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There is a nylon shim that can be made up and goes between the rack steering mount bracket and the rack horizontal cylinder body . I have seen them before for someone made a batch . If you look down through the engine bay you may see this gap easily , Lady P has it , this may be the source of your wondering . A power steering fluid flush " may " tighten up the rack if not a good idea to get rid of the operating grinding noise .
 
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Old 06-12-2017, 06:04 AM
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It strikes me that the only logical place to start is with a careful check of your tyres. Are they all of the same tread pattern, degree of wear, pressures, and in sound condition. How old are they?
It sounds as if something has caught your attention about the steering, which is obviously worth bottoming out sooner rather than later.
Thereafter a comprehensive checkover of all bushes and joints, front and rear, replacing as necessary, and finally a four wheel alignment check. The alignment can make these cars quite squirrely, but it isnt worth checking it if you then have to dismantle some of the suspension.
As you will know, they should sit nicely at speed, so there must be something adrift. Im not sure this is telling you anything you dont already know, so i will shut up!
 
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Old 06-12-2017, 07:29 AM
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The car has 87000 miles. I already have the nylon shims and there was not enough play in the racket to have it fitted.
I have 4 brand new bridgestone tyres.
I did an alignment but the garage said it wasn't necessary to adjust anything. The readings tell me nothing though. In norwegian but you might be able to understand the figures if you know how to read these things.

Countyjag is probably on to something regarding bushes etc. Change them all, I guess. But my god what a costly project
Front readings above. Rear below the line.
Venstre= left .
H°yre= right
 
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Old 06-12-2017, 07:33 AM
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I also changed the rear subframe bushes to the powerflex poly bushes..
 
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Old 06-12-2017, 01:34 PM
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I might be losing it in translation, but what were your toe in readings?
The rear right camber looks a bit off. The adjustment is achieved by putting shims between the flange on the diff and the driveshaft. According to my local dealer, they never sold any shims, factory settings remaining true. I couldn't understand why my car was so far out, then it dawned on me; someone had been working on the driveshafts, and when they reassembled it. The shims were swapped. Swapping them back had the camber bang on.
These cars are sensitive to rear alignment as well as front, and the rear toe is adjustable.
 
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Old 06-12-2017, 02:44 PM
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Toe in readings in red on the left side. Upper left for the front and lower red side for the rear.
 
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Old 06-13-2017, 01:37 AM
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I'm still not clear about the toe in readings. I would have expected to see 4, one for each wheel, as each wheel is separately adjustable for toe. At face value, the figures appear to suggest that the front and rear are "toed" in opposite directions, which doesn't sound ideal.
 
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Old 06-13-2017, 01:41 AM
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I'm still not clear about the toe in readings. I would have expected to see 4, one for each wheel, as each wheel is separately adjustable for toe. At face value, the figures appear to suggest that the front is under toe-d and the rear is over toe-d. Doesn't sound ideal, and strange that they would leave it like that as both are easily adjusted with a spanner. Are you sure they centred the steering before taking the front measurement.
I am sorry if this sounds like I am casting aspersions on whoever checked your alignment , but the results seem odd.
 
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Old 06-13-2017, 11:27 AM
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Did they check castor? For stability that is the most important reading, rather than camber or toe.

I have a 1966 S Type and initially I set the castor to 0 degrees, as is spec. Past 80 km/h the car was very unstable and difficult to keep in the lane. I dropped it to 3 degrees, which is the most I could physically do, and the car is now stable and drives nicely at 130 km/h ( the fastest I have gone).
 
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Old 06-13-2017, 12:00 PM
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I agree with Jagboi about castor, BUT i do not believe there is any castor adjustment available on the X300. Happy to be corrected if I have misunderstood this.
 
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Old 06-13-2017, 04:48 PM
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'Tis the camber that's not adjustable

Cheers
DD
 
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Old 06-13-2017, 05:53 PM
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Adding shims to the driveshaft where it attaches to the diff is the prescribed method of adjusting camber at the rear .
 
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Old 06-14-2017, 01:11 AM
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Some interesting inputs here.. And i dont really have any answers. They did say that shims would be the alternative for the rear but it would be too time consuming, so they basically didn't want to do it. It might be better to leave this a specialist garage.
 
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Old 06-14-2017, 03:50 AM
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My 3.2 Daimler 6 used to tram line all over the place 4 years ago when I first got it. It improved with new decent tyres, then rebuilt front shocks, then all bushes. It doesn't get much use since I bought my XJR, but it has been my daily driver for the past month since I crashed the XJR, and I have come to appreciate the virtues of the slightly softer sprung Daimler with rebuilt front suspension.

While the 3.2 doesn't have the low-down grunt of the XJR, it winds up quite nicely and is quite settled and smooth around 90-100 mph. It is actually more relaxed at this speed than my XJR on our less-than-perfect NZ roads , which has made me wonder how a Daimler would go with XJR shocks but retaining it's standard softer springs... and a gearbox with 6 or 8 ratios which gives it better low-speed acceleration would be an improvement but a costly and difficult mod
 
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Old 06-14-2017, 10:45 AM
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Another thought, what size wheels do you have on it? The cars are known to be unhappy on bigger than standard wheels.
 
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Old 06-15-2017, 10:18 AM
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Standard size on the wheels.. I'm taking some time now to consider if I should try to attack this issue on my own or let someone else sort out all the bushes.. I've had the car since September and already spent a small fortune
 
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Old 06-15-2017, 12:33 PM
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That sounds like a good idea. The only way to do it your own way involves a lot of time and a shop that will offer free alignments. Some tire shops sell this, and I have taken advantage of it when moving shims around.

If you don't you'll never know if you did a good job with shim placement...
 
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Old 06-16-2017, 04:59 AM
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I have been following this thread with interest, and on the one hand can see that you have been offered much well intentioned and good advice, but on the receiving end it might all be a bit confusing and depressing!
Before throwing in the towel and handing the car off to someone else to "fix' i wonder whether it might be worth another attempt to more accurately diagnose the problem.
You say that everything is fine up to 60mph, which I would take to mean no knocks, rattles, vibrations or waywardness in the steering. You have not mentioned any knocking or rattling over bumps. At face value, this is good, and starts to point the finger away from the dreaded topic of bushes!
You mention that an upper ball joint is worn. I would replace it without delay, as it is cheap and fairly straightforward to do. If it isnt causing a problem up to 60, I doubt that it is the culprit, but it needs fixed, and is a distraction.
You mention that by 100mph, the problem is fully apparent. Do you have any recollection of how it was at 70? 80? 90?. I am not advocating that you drive it at these speeds again, as it all sounds rather dangerous, but if the problem came on progressively, I would start to think of the variable assistance aspect of the steering rack. In short, the amount of assistance is intended to vary with speed, the faster you go, the less assistance you get. If there was something sticking in your steering, you might be able to turn the wheel through it with power assistance, but not without. So when you reach a high enough speed for the power assistance to diminish sufficiently, the steering becomes sticky to turn. If you can jack the car up with both front wheels off the ground, you could try moving the steering from lock to lock with the engine off, to establish whether there is full range of movement and it is smooth.
Another thought might be to put the car in for whatever for of government inspection you have. I sometimes put a car in for an MoT test here, as it is a cheap way to get the brakes, ball joints and bushes etc checked over by an expert
 

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