SNS (Spinning nuts syndrome)

[PaulGover]

The front of my car was squeaking, so I took the front wheels off to see if the bearings were shot; they weren't, another story.
But putting them back on, one of the wheel nuts started to grip, but then spun round, at much less than 125 Nm torque.

The problem is that I'd used a 12-point hex socket that fitted my old car's nuts. That's a 3/4" socket. Wrong, wrong, wrong.
As documented elsewhere on this forum, they're 19mm metric threads not 3/4" imperial. The imperial socket is 0.5mm too large, and with the 12-point design, it barely grasps the tips of the stainless steel nut embellisher. Apply a little too much torque and the embellisher deforms and starts to spin on the nut inside.

The cure is to get a proper wheel nut socket such as this one from Halfords.

[BrianG]

An important warning, thanks Paul. I must admit that on rare occasions I have used a 12-point socket from my workshop imperial set, but usually I get the bog standard wrench out from the car emergency tool kit, so 6-point without problems.

[PaulGover]

Brian, I don't know if they changed the emergency tool kit wrench between your car and mine, but I don't think mine has sufficient leverage; it's about 15"/40cm long. Or maybe I'm getting a bit feeble in my old age... For comparison, the wrench in my 1991 XJS's kit has an extension to increase it's length to about 2ft/60cm.

I had to get the breaker bar out for the exercise mentioned at the start of the thread - the tyres were changed a couple of months back, and the air gun must have been turned up to 11! Done up correctly they're still 125 NM, 90 lb-ft, which is pretty tight. Torque settings seem to have increased in general XJS-X350.