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Jacking the JB74 and the Mystery of the Handbook

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08 Jul 2022 13:37 #244004 by Doctorchris
I've been rotating my tyres for the 3rd time and noticed a bit of contradictory advice in the JB74 handbook.
Page 7-3 advises positioning the garage jack, to raise the rear of the car, under the differential. I have found this arrangement satisfactory on several occasions.
However page 7-4 advises that you never apply a garage jack under the rear differential.
Which piece of advice is correct?

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08 Jul 2022 13:50 #244005 by Gadget
I believe it means don't jack on the diff pumpkin itself, jack on the bracing plates to the side of the pumpkin.

To be honest I only ever jack using the dimple bits on the radius arms, which is what it says to use for the supplied jack, not sure why they say to use different points when using a trolley/garage jack?

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08 Jul 2022 14:50 #244006 by Doctorchris
Although the illustration in the handbook shows the bracing plate on the front axle to be the jacking point, for the rear axle it clearly shows the pumpkin (as you amusingly call it) as the advised jacking point.
I would use the ends of the radius arms but it just takes more of a lift to get the wheel to clear the ground.
It's not a big deal, just wondered why the contradiction.

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25 Nov 2022 09:47 - 25 Nov 2022 09:48 #246104 by Motacilla
Reviving a spring thread for the winter tyre-changing season...

Like Doctorchris, I was initially confused by the handbook's warning never to apply a garage jack to the differential, a warning that comes one page after an illustration pointing to the rear differential as the jacking point.

In the end, I decided that what the handbook was meaning to say is that the differential components -- ring gear cover and nose piece -- should never be used for jacking, but that placing a garage jack with due care under the axle housing, at the center, was correct.  

But I would love to hear if someone has better knowledge (or strong feelings) on this.  I would hate to be wrong...
Last edit: 25 Nov 2022 09:48 by Motacilla.

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