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Jacking rear of car uner diff

Calaber

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Recently, I had the rear tyres replaced on my car. The young bloke who did the job ran the jack under the rear of the car and proceeded to place it under the diff, then jack the the car up. I didn't see him doing it until I noticed the car was off the ground and the jack was under the rear. I immediately told him that was incorrect and the diff centre was not the proper jacking point for an IRS Holden. I said I didn't want the diff carrier bent and that the factory manuals says not to use the diff as a lifting point. I asked him to drop the car back to the ground and use the sill lifting point.

He said he has always done it his way, but I told him what I wanted, so he did as I asked.

Now, has anybody else had problems with their diff carrier because of incorrect jacking procedures by garages, or was I being a bit precious? Is it safe to jack the rear by using the diff centre as a lifting point or not? I've always used the sill and will continue doing so, but I would have thought a tyre fitting business would be more careful and aware of the correct jacking procedure for such a common model of car.
 

walesy

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my currant car is too low to get to the diff center with a big enough jack, but I have always used the diff center to jack up the rear of a car then put stands under the car, its just easier and ive never had any issues doing it
 

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i wasnt aware the manual says that,ive always lifted the rear of my irs cars with a jack under the diff,seems to be ok,what business was it for interest sake as you'll find that nearly all tyre shops do that?
 

Calaber

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I won't nominate the business - he's only a small trader and has been very fair with his prices. It was one of his staff who I dealt with. I mentioned it to the owner and he said he would talk to the fellow.

I have had a look at my workshop manual (Ellery's) and it refers to jacking the rear up under the diff then placing the car on stands, so perhaps I have misread this item somewhere, but I was sure I had seen a warning in a genuine shop manual some time ago stating that the diff was not to be used as a jacking point. This made sense to me because the diff cradle has a propensity to crack and it's not designed to take the whole rear end weight of the car in the centre - that job is for the outer mountings of the cradle, near each wheel arch, where the suspension arms are pivoted from. When the car is on the ground, its weight is distributed at the back between the two tyres and the weight is transmitted directly into the subframe structure by the design of the cradle. By jacking it up in the centre, the complete weight of the rear of the car is focussed on the cradle, but not below its inner mounting points. In my thinking, the concentration of the weight in an area where the cradle could be damaged by bending, could eventually lead to the cracking that the cradles are known for.

I might be wrong - it seems others here use the diff for jacking, but I'll stick with the sill locations.
 

walesy

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yeah that does make sense calaber, spose its up to you, its your car and i spose we all do things in different ways
 

VYMAD

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I can see your point, Calaber, but I found out off this forum that it was ok to jack up the rear of the car off the diff. Before reading that on here, I would NEVER have done so. Since then I've done it a few times and hasn't caused a problem.
 

Calaber

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I'm damned sure I've seen a workshop manual which has the jacking points highlighted and states clearly that the IRS diff is not to be used. It was quite a while ago, and ever since I bought the VY over three years ago, I've always jacked it up using the sills. It would be interesting to see if there was any sign of bending or other damage on the cradles of cars that have been regularly lifted under the diff. Have any of you guys who jack the car up that way, ever had to replace the cradle and perhaps just put it down to metal fatigue?
 

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vt onwards had very strong cradles that very rarely crack from what ive read,its more so vn-vs that crack ands its usually from giving it a hard time,burnouts etc
 

VYMAD

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Well, like I said, only done it a few times, with no apparent problems. I, too prefer to jack under the sills even with a trolley jack.
 
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