jacking and racking points - again w/ SWB

[tadink]

sorry for the redeaux on this topic, but I've got an issue with where to place the jack stands on my early SWB.

After reading ALL the posts about where to place the jack, I went with the engine block jack placement - careful to use a 2x4 to spread the load a bit. I placed the jack stands on the torsion tube ends, and lowered carefully.

This is where my concern arises....how much flex is there on the torsion tubes? As the jack stands begin to take the load, the tires are still off the ground and able to turn....but as I lower, the torsion tubes take the load and the tires come down to the ground. I think there is about an inch or more of 'flex' coming from somewhere....and I fear the worst.,,,,,.....that dreaded R word!!!!!

Grady cautioned me to check the torsion tubes carefully for rust, and I just don't know how / where to look....this is the first indication that there may be some deep rot in there somewhere....

one thing that I'm hoping is happening is that the geometry from front to rear is taking over and that heavy engine in the back is causing the front of the car to raise a bit, effectively lowering the rear wheels to the ground? that is CLEARLY hopeful thinking!!

where else could I place the jack stands to keep the rear end off the ground allow me to remove the rear wheels, and access the underside. I'm naturally a bit hesitant at this point to put my body under something that heavy and potentially unstable....guys, can you help>>/?????

[HarryD]

As you may guess, this topic has come up numerous times and us old timers generally respond with a suggestion to use the search function here to find the information.

So.... Use the search function with the key words jacking points.

If you do, the third or fourth thread (All the jacking points??) will have all your answers.

In the picture of the jacking points , directly under the letter D are the torsion bar tubes. These are what you need to inspect.

There are other posts listed as well that can provide yet more answers about correct lifting and supporting of your 911.

[pozee]

tadink,

I don't have a technical answer to your question about tube flex. However, I do know that rust has very little to no flexibility - it'll "give" but rarely bounces back.

Are you using jackstands with a notch or flat surface? A notched surface will allow the torsion bar tube to settle, allowing for some movement. Do you see the tubes bent with the load on them?

Good luck and think positive - No "R"!

[tadink]

Thanks HarryD and Pozee for your responses....and I have searched and read the numerous posts on the subject of where to place the jack stands....however, my question is more of a behavioral one - how does the car 'settle' onto the stands when I'm using the torsion tubes?

It seems that when the tubes first make contact with the stands, everything is fine, however as I continue to lower, the wheels then touch the ground. I'm hoping that this is just the fore and aft settling that I'm seeing, the front end raises a bit as the back end's weight pivots over the jack stand. Maybe I should have formed that as a question????

I just saw the ugly rust repair thread and I'll go read that now - hoping for the best the whole time!!

thanks all - any help very appreciated....

tom

[pozee]

I should clarify. When I wrote about "settling", I meant that when I have used a jack stand with a notch, I have experienced the torsion tube to sit up against the edges of the notch and then settle further as the notch corners dig into the undercoating - as I continue to lower.

I have not experienced the torsion bar tubes to be the pivot point in long or short hood cars. Not sure about SWB though.

Do you see the tubes flex when the weight is on them? I don't think they should.

[burgermeister]

When you are jacking the car up under the crankcase, you are rearward of the rear axle centerline. This will add load to the front tires - the engine is no longer acting as a counterbalance on the other side of the rear axle. So, the front dips down.

When you transfer the load onto the torsion bar covers - which are located in front of the rear axle centerline (probably only 500mm rearward of the CG of the car) - the opposite happens. The engine (and rest of the rear end) is now a counterweight with a bigger moment arm. This will take load off the front tires. Front of the car goes up, rear goes down, all of it pivoting about the torsion bar covers.

Also, the covers are connected to the car with rubber bushings. Using them to carry load will cause some displacement. Place the jackstand as far inboard as possible without hitting the cover plate that holds the spring plate in.

[tadink]

Burgermeister! Thank you! I think that is what I am seeing....I'll run through my jacking process again and keep an eye on the front of the car....and I suspect that the pivot is around the tubes! whew....not so say that there still might be some "R" issues in there, but I don't see the tubes deflecting or bending under load, and as stated before, rust is not resiliant - ie it does not 'bounce back' once compressed.

thanks all who helped me on this....what a great resource to have!! the collective brain!!

cheers

td