Extension makes the geometry of the support cup lethally unsafe.

As the lift arm moves up through an angle the support cup has to pivot so it stays under what you are lifting. The flat pivoting bar underneath the main lift arm acts, parallelogram fashion, to hold the cup horizontal so all is stable. Without the stabiliser the cup will flop all over the place and probably let the jack squidge out from under rather than lift. The condition for stability is that the weight be applied behind both the cup pivot and the lower stabilising arm pivot keeping the stabilising bar in tension. Being a flat bar the stabilising arm will buckle easily in compression, getting out from under the load so the cup pivots and, most likely, everything falls off.

Theoretically during lifting and lowering the jack slides along on its wheels keeping the load safely behind the pivot. In practice these small jacks rarely run dead smoothly so the load shuffles back and forth a bit pivoting the cup as it does until enough force is generated to move the jack over whatever obstructed it. The jack moving force generated is roughly proportionate to the anglular shift of the cup. With the extension piece the amount by which the load shifts for any change in cup angle is much greater than with a plain cup. So it doesn't take much before the load is beyond the stabilising pivot. Whereupon the stabilising parallelogram flips, the cup flops over and fatty falls off.

Not theory. I've actually encountered this effect with a small Weber jack modified to take a larger cup giving maybe 1" or 1 1/2" lift to the cup. Geometry said it should have been safe, just, but hurry up and won't listen mate took it right to the top instead of using a raising plank and crash.

Those short chassis high lift jacks move the arm through far too large an angle requiring a matching movement of the jack.

There are darn good engineering reasons why the "good old" higher lift jacks are so long and move the arm through much smaller angles. Realistically anything beyond 35° is getting iffy. I have a Northern Tools long reach 2 ton jack, similar to the Clarke CTJ2GLS, bought years ago. Hefty brute but effective. Maximum lift is around 800 mm but the 660 mm or so of the Clarke is a much more sensible and geometrically safer limit. The gyrations at the lift cup and corresponding jack pull forward over that last 200 mm are horrible.

Clive.

Last edited by Clive603 on 13th Oct 2017 3:50pm. Edited 1 time in total

Overspec your jack and stands

I have an ancient "Duco" 5 ton trolley jack (only gives about 9/10 inches at most) and 6 ton axle stands (each)

Like stan, jack the rears under the wishbones from standard EAS height (this makes the wishbones almost level). Then you can get an axle stand under the jacking point.

At the front I tend to go to offroad height, then jack under the jacking point with the sprinter, then axle stand under the subframe near the rear control arm.

If the whole car is going in the air, then I use my acme oak sleepers (still going strong 5 years on), and jack up from there.

When ever jacked up I usually have three things stopping the car from coming down on me (who would be a Health and Safety Officer?): jack, stand, tyre, wood block, wife.... .
Experience is the only genuine knowledge, but as time passes, I have forgotten more than I can remember
Volvo V70 P2 2006 2.4 Petrol 170bhp Estate SE
MG Midget Mk1 1962

Previous: L322 Range Rover TDV8 3.6 2008; L322 Range Rover TD6 3.0 2002; P38A Range Rover V8 1999

i like your 'acme oak sleepers' Tim but every time i go to get some a bloody train comes along..... ... - .- -.




Y. O. L. O.
.

stupid boy  .
Experience is the only genuine knowledge, but as time passes, I have forgotten more than I can remember
Volvo V70 P2 2006 2.4 Petrol 170bhp Estate SE
MG Midget Mk1 1962

Previous: L322 Range Rover TDV8 3.6 2008; L322 Range Rover TD6 3.0 2002; P38A Range Rover V8 1999

I used one of these http://www.costco.co.uk/view/p/arcan-2000k...0eu-900930

I have several other professional trolley jacks that are rated at 2.5 and 3 tons, but I found that lighter 2 ton jack was more than enough to lift an L322, although the car weighs in at approx 2.6 tons, you have to remember that it is spread out over 4 wheels, so the most you'll be lifting is 1.3 tons..... it is probably more like 1.5 tons front and 1.1 tons rear.... so unless your stupid enough to try and lift all 4 wheels at the same time a 2 ton jack is more than enough.

As for the LR jacking point.... good luck with that one... the exhaust is rather narrow at the "jacking point" I found it easier to lift the rears a corner at a time then lift the front in one go... much easier to find a cross member to jack on  Yesterday I couldn't spell Engineer... Today I are one!
Inventor of the 'Guide-o-Matic automatic wheel alignment tool'
Former long term L322 owner, Up/Down graded to a Classic Tractor!

Snapon dual pump does it no problem fast pump to height and then jack it up. I use the original jacking points