Hello all.
So I noticed a weird behavior on my xj6.
This happens when the road is heavily wet and going uphill on a freeway.
From time to time you feel like a kick in the back like if there were a traction problem, lose of traction for a fraction of second. This driving at constant speed uphill on a freeway like 65/70 mph

The same thing happens if the street is heavily wet and I drive on a bridge when I cross the metal joints on the road. Feels like a kick, lose traction for fraction of seconds and gain traction again.

this does not happen in any other situation.

Could this because the rear differential is not limited slip ?
thanks

 

Very few X300 are fitted with limited differential, I heard, and if what you described happened on a straight road rather than cornering, it is unlikely to have anything to do with the differential. Do you have traction control instead, and if so, was it on or off at the time of driving? Whatever, the first thing to check is your tires if all such incidents keep happening when road is wet. How old are your tires and how much tread is left? Some tires are good on dry surface but scary when wet, or are good when relatively new but will lose gripping power once the premium layer is gone.

 

Look fwd of the ABS module and you will see a vertical cylinder with throttle cables coming out of the top as this is the traction control actuator .

 

hmm are you sure there is a traction control ?
I read that on the xj6 US version traction control was a option and usually
not available on standard xj6 unless you payed for this option. When the behavior I described happens I have no light showing up on the dash. How can I verify if I have traction control ? if the street is wet in a curve and I push the throttle down all the way, like on a freeway shoulder, the car start oversteering nicely so I guess no traction control at all?

 

hi and thank you. I have brand new tires (600 miles on them). I have no traction control switch on my dash... I guess I have no traction control at all probably ?

 

Yeh, traction control is as rare as limited differential on the X300. But what you described is obviously a surface traction issue, like you said it happened when crossing the metal joints on the bridge. Both my XJR6 and X350 have traction control, and with the X350 the experience with skiing and correction is exceptionally noticeable. I can feel the car ski for a fraction of a second but quickly regaining traction, and every time it happens the dash warning light flashes to tell you traction control just kicked in. The back-to-grip feeling is not like a kick though, but the slip is almost like you yourself slipping. I heard new tires need running in, but 600 miles would be enough to have done that. Whatever, I would be very careful with those tires on wet surface, particularly if you don't have traction control and unsure of the health of your ABS. X300 is a very heavy car, so losing grip on the highway when wet can be very scary.

 

Mine is a SWB Sovereign and has traction control because she's special , just ask her .

 

the ABS is working I Tested it... anyway it is not something happening normally but I was just surprised to notice it...

 

Traction control is a extra option that uses the wheel speed sensors of the ABS to throttle back the engine during rear wheel spin and put a light on your dash while it is correcting . Look for the actuator fwd of the ABS module . The wires under the cylinder have a history of poor insulation that disintegrates exposesing the center conductor , can be repaired . I think this mode of failure causes the actuator to not respond as the upper position sensor is the followup feedback the give you a fail light if not moving to the commanded position .

 

Tyres vary hugely in the wet.
My xjr has 18” Bridgestone RE-003s and they grip forever - even in the wet they never slip, unless I turn off Traction, and deliberately drop the clutch.
On the other had my old Ford has some Falkens which should be good, but seem to be made of plastic and spin with the slightest provocation in the wet, and that only has 240 bhp compared to over 300 on the XJR

 

Wish I had a XJR too, you're lucky...
my XJ6 has only 245HP
my tires are new but they are the cheapest as possible: Doral.

 

Cheapest possible may explain it.
I never go cheap on tires, esp an 1800kg car that can exceed 120mph

 

well most tires are very similar even if different brands. I agree Michelin are much better. But they cost more than twice.
Doral are cheap but after all not bad. Also in California you may not want to exceed 70/75 mph unless you want to be jailed. they are the standard tiers rated for correct speed for this car. I did not install under rated tires, just the cheapest according to proper specifications. I also have the same brand Doral on my xj6 III. On that one I did not notice this behavior, probably because I drive slower with that car, and anyway the engine is much less powerful.

 

There is a rating on the side of the tire that give the traction grade A-C with C being the worst with Michelins being the A rating . This has nothing to do with the snow tread or water displacement pattern but the quality / cost of the rubber compound . Age will degrade the rating .

With the date stamp and tread left on the Michelin's installed on mine she did 20 K in 10 years . It was broke down behind the curve in a garage .

There is a load rating as well .

Had some C's on a rental car in France that wouldn't go up a mountain to go skiing is how I found out

 

I had a good lesson the other day. While cruising on a flyover, I heard unusual tire noise and felt vibration from the rear right, and as soon as I was off the flyover and stopped I found the rear tire entirely flat. Took the car to a tire shop and when the wheel was taken off the car it showed that the tire was shattered into pieces - the tire wall was entirely gone and tire surface where it met the ground had a nail (I took a picture but couldn't find it from my files). I recall it was a very short trip (maybe 15 km highway non-stop traffic) so it was sort of weird that the tire failed so quickly to the stage of no repair. The shop attendant said my Jaguar is a very heavy car, and should use tires with stronger tire wall to stay in shape, especially when there is a puncture - modern tires can last a while with a minor puncture.

I have a dozen of tire punctures over nearly 40 years of motoring (mostly caused by nails - very common in Hong Kong as we have many road works as well as residential and office building fitting out work), and hence I made it a habit to have a visual check on my tires before rolling off. That was the first that the tire was entirely destroyed within a very short time. Maybe the nail went in at an odd angle that killed the tire, but I was very disappointed as the tire was very new, was OEM and a branded tire on a sports car.

That tire, Dunlop Sport Maxx (Made in Japan in 2017), only had 1,000 km before being removed from a new Subaru STI and installed on my XJR, and I have about 7,000 km on those tires when the puncture happened.

The XJR is nearly 1900 kg (the NA version weighs 1,800) so imagine how much safety you count on the tires, stopping in time, running on wet road and bad weather, and enabling you reach the point of rescue if and when you have a puncture. I am thinking of switching to run-flat tires in the next change for the peace of mind.