Any idea what the torque should be for this nut:


I don’t see anything in the book, but I’m guessing it’s a Brit vs American terminology issue.

 

It's not torqued. You tighten the nut just enough, just beyond hand tight, to take up all float in the bearings, then back it off slightly to allow .002 to .005" end float. Then put the nut retainer and cotter pin on.

 

Well that sounds scary. So the cotter pin is the only thing securing the nut? And the nut is the only thing holding the hub and disc in place? I guess the caliper helps too, but still…my MR2 axle nut took something like 140 ft-lb. Hand tight doesn’t inspire confidence.

 

No worries. Your XJS has the old school hub arrangement used on umpteen millions of cars...until sealed hub/bearing assemblies came into vogue.

Cheers
DD

 

Millions of cars are and were built that way. It's never been an issue.
The worst thing you can do with the XJS front wheel bearings is overtighten them and then run them that way. As the hubs warm up clearances are reduced.
The sealed bearings you are used to are built as a unit, with clearances determined by manufacturing tolerances and the preload. The XJS bearings are independent of each other, and are adjusted in a different manner.

 

Thanks for the explanation and reassurance, Jal and Doug. This forum is a help yet again, no surprise there.

 

If you have not done this before, then this is what works for me:

1. do up the nut until there is definitely NO end float - not stupid tight, but definitely no float
2. you will then find you can turn the hub but definitely feel it is resisting, with a slight binding feel
3. turn the nut back about 10 minutes on the clock (ie 30 degrees or so)
4. then try turning the hub and if still a bit of resistance, undo five minutes more
5. if loose do it up a touch
6. you will get the hub to the position where you can feel it is turning nicely but not loose (loose meaning you can grasp the disc and move the hub in and out a touch) and not at all binding. That's where you want to be. Sounds a bit worrying, but when you do it in practice you will find the right point is quite easy to locate.

Modern cars have sealed bearing packs as Doug mentioned, and these packs have a spacer between the inner and outer bearing as part of their assembly. This makes it impossible to overtighten the inner and outer bearing together on the stub axle, as the spacer resists the torque load and ensures the two bearings are not able to bind. What you are doing in the above routine is setting the correct "clamp" effect between the inner and the outer bearing.