torsion bar and ride height question

[Chris Pomares]

I'm working on a SWB car. 19/24 torsion bars with SWB spring plates mated to SC/Carrera adjusters. The car is on my lift. The car is exactly 1.8 degrees nose down on both sides. With my digital level I measure 33.5 degrees on the upper edge of the adjuster not the spring plates. To get a matching rear ride height when on the ground (24 and 3/4 inches) the spring plate angles are different by 1.3 degrees.
Question? Tired torsion bars? Slightly bent car. For those who have many years of experience what do you suspect. I have a new set of 25 mm Sway Away torsion bars I can install to see if it's bars but before I do that I thought I'd run this by you guys.
Chris

[chris_seven]

Well within tolerance and I wouldn't be concerned.

Early bodies weren't that well jigged and if you add up all the manufacturing tolerances and the position of the SC adjusters that have been added to the spring plates I don't see much to worry about.

The idea that Torsion bars 'tire' isn't quite what it seems. It is possible that a spring can take a set after a significant amount of use but this is normally associated with springs that have changed section due to corrosion or some other damage which results in a change in cross-section.

If we examine cyclical fatigue curves it can be seen that for each succeeding cycle the linear elastic portions of all load/deformation curves exhibit the same slope.

That is to say, the elastic modulus doesn’t change with more plastic fatigue cycles. Since a lot of the major material property changes under cyclic loading tend to happen early on, this is a good indication that the elastic modulus remains constant.

It is the elastic modulus of a material which creates the 'spring effect' in steels and this is governed by the shape of the interatomic potential energy curve and microstructural alterations such as the dislocation substructures that form during cyclic fatigue won’t affect the shape of this curve and thus have no effect upon elastic modulus.

In fact, this theoretical point can be regarded as the reason for the first point above that progressive cyclic fatigue data exhibit no σ-ϵ slope changes in the linearly elastic part of the curve.

[76911S]

In other words, early cars are not all that square to begin with, have you seen the period photos of the assembly area's, and we have all heard about the beer ..

Mark..

[Chris Pomares]

Chris and Mark,
Thank you both. I'm within a 1/16th of and inch 24 and 3/4's rear and 25 and 1/4 front. I'll leave it be. Chris, I'll have to go back to school to understand everything you wrote. But I did understand this part.
Chris.

"Well within tolerance and I wouldn't be concerned.
Early bodies weren't that well jigged and if you add up all the manufacturing tolerances and the position of the SC adjusters that have been added to the spring plates I don't see much to worry about."

[keith]

I don't necessarily trust the fenders - are your heights even to the lower spring plate bolt on each side? how about up front - heights even between the crossmember bolts and your level rack surface?

[66S]

Try lifting the front end in the center when doing the measurement. Maybe the front bars are influencing the rear ride height.

[Haasman]

This might help-
Porsche 911 European Ride height.pdf



<script type="text/javascript" src="safari-extension://com.ebay.safari.myebaymanager-QYHMMGCMJR/5df9a8c/background/helpers/prefilterHelper.js"></script><script type="text/javascript" src="safari-extension://com.ebay.safari.myebaymanager-QYHMMGCMJR/5df9a8c/background/helpers/prefilterHelper.js"></script><script type="text/javascript" src="safari-extension://com.ebay.safari.myebaymanager-QYHMMGCMJR/5df9a8c/background/helpers/prefilterHelper.js"></script><script type="text/javascript" src="safari-extension://com.ebay.safari.myebaymanager-QYHMMGCMJR/5df9a8c/background/helpers/prefilterHelper.js"></script>