Question about jack points

[dicer]

I guess its the little things that get to me at times. Spent sometime searching the net about jack points.
I just find it funny, sad or ? That so many cars have rocker panel pinch welds as designated jack points, that is an engineering fumble that is just asking for trouble IMO. Since the surface area on a pinch weld is about as much as a kitchen knife and how any side movement could easily collapse it, then allowing the jack to dimple into the rocker area saying nothing about ruining the paint and opening it all up to corrosion. All I can see is it was a great cost savings in the manufacturing process and not proper engineering, especially on my favorite older luxury car that should have been something better. With all I have found on the net about the subject of ruined pinch weld jack points, why has no one that uses this method designed a designated FLAT hard point to jack and lift at that is not going to bend and lose paint every time the car is lifted or jacked?

 

[dgallup]

You don't load the knife edge, you load the flat surfaces on either side of the knife edge.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[dicer]

Not on an LS400 you don't. A careful study of the factory scissor jack pad tells the story as well. Any place off the pinch weld is asking for bent metal.

 

[BrianPetersen]

The bending strength at the pinch weld is much stronger than the surrounding area. In tech terms, the moment of inertia of the load point is much greater for a vertically-oriented chunk of metal than for a horiontally-oriented piece, when the load being imposed is vertical.

Illustration: Take a flat piece of cardboard. Lie it flat on the table. Pick it up by supporting it from underneath at the middle. It bends. Now turn it on its edge and do the same thing - granted, you will have to keep it from tipping over, but the point is, it doesn't deflect (appreciably).

The pinch weld also serves to lock into the jack that was originally designed for the vehicle so that the jack doesn't slip sideways. I don't know about that particular vehicle, but the scissor jacks that are typically designed for OEM, have a notch in the pad that is meant to lock into the pinch weld so that the jack doesn't slip sideways on the vehicle (top) side of the jack. 'Course, the manufacturer has no control of the surface that you are placing the bottom of the jack on.

Yes, I know what happens when people use the incorrect jack for the vehicle, or they put the jack at an inappropriate location, or they jack a vehicle on an unstable or sloping surface. Yes, I know that sooner or later it will go through the paint.

A lot of vehicles have various combinations of the following as countermeasures against corrosion in that area: Galvanized structure, sprayed-on anti-chip coatings on top of the paint, plastic under-trays that overlap the pinch weld.

 

[dgallup]

I'd like to see that jack. All the factory jacks for all the cars I've owned in the last 40 years (obviously a small subset of the vehicles out there and none of them lexus) have had a slot that straddled the knife edge and picked up the car on flats on either side. The knife edge does add considerable sectional strength but you wouldn't want to lift by it. The only time my vehicles have been damaged underneath is when they were picked up buy 4 arm hydraulic lifts that the mechanics poorly positioned elsewhere.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[dicer]

Yes it is meant to lift the knife edge of the pinch weld. Yes a rid is beam like but still a nonsense deal. On quality stuff do quality things. A pinch weld can be spread and bent over as you can't always chose where you need to change a tire. Mercedes seems to get it right. Oh the Lexus jack has a slight very wide impression not a nice tight fitting hard plastic insert like it should have to protect the paint finish on the pinch weld.

 

[GregLocock]

Our 2 post lifts have slotted pads for the reason dgallup gave. Having said that our old school mechanics prefer to lift on the frame to rocker cross member or the IRS mounting point.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[GregLocock]

the above shows what claims to be the jack from an LS400 and is designed like any other OEM wheeljack I've seen lately, it has a slot for the flange.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?