Jacking cars and bending them...

[dailydriver]

Originally Posted By: ls1mike
The Trans Am is hard to lift. I usually, if working on the rear of the car, lift it up from the rear diff then put jack stands where the lower control arms mount to the unibody.

The front is tricky, but I lift from the sub frame and it is pretty solid even with the T-tops.


Yes, and one would think that the stealerships would KNOW not to put the lift blocks/arms on the point where the front fenders bolt to the unibody on 4th gens, since it says right there "DO NOT JACK OR LIFT AT THIS POINT!", AND I forewarned them (the writer and service manager) as well about this since the tech they had replacing my fuel pump probably has NEVER worked on a 4th gen before.
But NO, of course they went ahead and gave me the 'heat vents' behind the front wheels ANYWAY!!

 

[CBR.worm]

I have noticed with multiple cars of mine over the years that with a single corner lifted, the doors don't open/close properly.

 

[morris]

at one time there was such a thing as a FULL FRAME. DA

 

[JHZR2]

Originally Posted By: morris
at one time there was such a thing as a FULL FRAME. DA


Yeah but what started me thinking and posting this was a comment I read elsewhere about how a body attachment point broke off when lifting a full frame truck!

 

[Shannow]

Originally Posted By: morris
at one time there was such a thing as a FULL FRAME. DA


Yep, and if you do the math on the torsional stiffness of a ladder frame....you will be appalled...then compare it to the torsional stiffness of a box attached to the ladder frame, versus a box flexibly mounted to a ladder frame...you might be surprised.

 

[hattaresguy]

Originally Posted By: xfactor9
Cars with very large windshields (front or back) are at risk of cracking the glass from body flex. Some mid-engine exotics, because they are very wide and have large front windshield, will crack the windshield if you lift by one corner


Old stuff maybe, like a Countach or Diablo.

I'm pretty sure you could lift up the modern carbon fiber cars from one corner and they wouldn't flex at all.

Its like convertibles, most of them like the old CLK's were horrible, and anything American is like a wet noodle.

These days? A Porsche 4S cab seems to be made out of billet, flex? Cowl shake? Young drivers don't even really know what those terms really mean anymore.

 

[The motor guy]

ok so my owners manual says to place a jack stand right behind the wheel well on the pinch weld of the frame. Is there a better place the jack up the front of the vehicle cause the frame just flexes and the tires go back on the ground even though I had them completely up in the air before setting it down on the jack stands. This is a 2wd truck so there is no front axle for me to place stands. Just I just need to jack it up higher to combat the flexing of the frame? I'm not really that comfortable doing that cause my jack stand is like all the way up as high as it will go. There has to be a better place that doesn't put so much flex on the frame. That can't be good.

 

[rationull]

Originally Posted By: motor_oil_madman
ok so my owners manual says to place a jack stand right behind the wheel well on the pinch weld of the frame. Is there a better place the jack up the front of the vehicle cause the frame just flexes and the tires go back on the ground even though I had them completely up in the air before setting it down on the jack stands. This is a 2wd truck so there is no front axle for me to place stands. Just I just need to jack it up higher to combat the flexing of the frame? I'm not really that comfortable doing that cause my jack stand is like all the way up as high as it will go. There has to be a better place that doesn't put so much flex on the frame. That can't be good.


Are you sure the frame is flexing, or is the vehicle just settling down on the stands as its balance changes as the load is transferred from the jack to the stands? How high do you have the stands set?

 

[Robenstein]

True modern cars will resist body flex a lot more than the older unibody cars. I remember just driving early Camaros, Firebirds, and Novas with strong engines could warp the body. My Nova flexed enough taking a corner hard to pop open the doors if they were not locked.

I think its possible to tweak them but much less likely. Im usually more worried about pinching a line for the gas or brakes in my head than twisting the chassis.

 

[artificialist]

I used to seeing this on convertibles, and on the cheapest compact cars from the early 1990s and before.

 

[JHZR2]

Originally Posted By: rationull

Are you sure the frame is flexing, or is the vehicle just settling down on the stands as its balance changes as the load is transferred from the jack to the stands? How high do you have the stands set?


I would imagine that the jack stands flex a bit when taking the weight too...