Will Aluminum Trailing Arms mated to Early Steel Spring Plates limit Aligment Ranges

[rboylan]

Boys,

I was working on a rough aligment to test drive my '70 Turbo project, it appears my rear toe adjusment is maxed out and the rear wheels are uncomfortably toed out. The eccentric bolt is maxed out and I'm worried there may be an issue with the interoperability of later aluminum trailing arms and early steel spring plates. I know Porsche changed spring plate design in mid-1976 but I don't know if it is necessary to update the spring plates to accomplish a precise alignment.

Does anyone know if the post '76 spring plates offer any increased range of adjustments ? The car is a '70 with '70 spring plates and 77 aluminum trailing arms. Thanks guys.

[911pcars]

Not sure if this adds anything to what you''ve found so far, but I have ~77-78 al. control arms with SAW adjustable spring plates on my '69. As far as I know, the toe and camber holes in all the long wheelbase spring plates are the same (however, the camber and toe eccentric bolts are not).

How did you determine there is no more adjustment? Vehicle on floor, driven to settle suspension, then measure?

Sherwood Lee
http://members.rennlist.org.911pcars
www.seinesystems.com

[rboylan]

Sherwood,

Thanks for the prompt reply. I'm doing an "old school" rough aligment utlizing stationary blocks on all four corners with string running square aroung the vehicle. Whilst I watch for changes in space between string and tires, my father is adjusting the eccentric from underneath the vehicle. The car is seated on CBS blocks so there is enough room to wiggle under and make adjustments. As the toe adjustment was was moving in the right direction, we ran out of range on the spring plates. Any input would be appreciated. I utilzed the later style eccentrics because they are longer and necessary to fit the aluminum T.A.'s.

[jluetjen]

You might want to try backing off on the camber a little bit so that the camber ecentric is in the middle of it's range. In some cases, removing the camber eccentric and putting it back in 180 degress from where it was will help. After working with a local alignment shop on my car I've come to the following two conclusions.

1) The porsche system of alignement really doesn't have a wide range of adjustments. But there are newer parts (ie: adjustable spring plates etc) that address this problem.

2) Using the stock pieces, keep in mind that the total alignement "universe" roughly equates to a circle if you think of the camber vertically and the toe horizotally. If you have either adjuster maxed out, you will have very little or no adjustment of the other axis.

[Clark Griswald]

You didn't say if the car has been lowered. That will limit your range of adjustment.

You can elongate the slotted adjuster holes in the spring plate to gains some additional range.

You can test to see if this will help your situation without machining by removing the bolts and using smaller diameter ones to simulate the longer slots. This is just to test and determine which holes require machining and how much.

[fred cook]

One other small thing to consider, is that dissimilar metals in contact tend to set up a galvanic action that will cause corrosion
with one of the metals (probably the aluminum) getting the worst end of things.

Fred Cook