Rear torsion bar ride height adjustment

I would like to reduce the ride height of my car to Euro spec.

The front ride height adjustment seems straight forward, the procedure in the Haynes manual could not be much simpler. I am aware that I need to remove the spacers on the top of the front shocks.

Now, I look at the back & quite frankly I don't know what I'm looking at!
I've read the procedure & know that I want to turn the spring plate & torsion bar relative to each other,
but what does this really mean?

Can anyone explain it to me in plain english.
And honestly is it a really big deal.
I wanted to set the ride height myself & then get a shop to do the alignment.
The quotes I've had for the lowering work are enough to curl your hair.

On the subject of alignment, will a Porsche specialist do a better job than a good tyre shop.

The Porsche guys charge around 3-4 times more .
I doubt there is much difference, if anything a good tyre shop will probably have more up to date alignment kit.

I'm trying to save money where I can. After years of motorcycle racing/ownership I have a good stock of tools & a modicum of mechanical aptitude. Am I running before I can walk & just put the car into a dealer or is the job do-able?

JG

See Pelican Parts tech articles. The procedure is fairly straightforward, but time-consuming.

Okay, I did read this but still not too sure.
Does the spring plate have to be removed completely to alter the ride height?

The word spline to me implies that the whole assembly needs to be taken apart & then assembled again.

Can anyone help on the alignment quandry?
Will a Porsche shop do a better job?

You have to pull the spring arm off far enough to get your hand on the torsion bar and rotate the bar in relation to the spring plate.

I lowered my car last month and to do the job right you have to corner-balance it at the same time. My corner weight was off 100 lbs. after lowering and before corner-balancing. After corner-balanceing the weight is within 10 lbs. It takes a little time and that is why it is costly.

I would and did take my car to a Porsche shop for the alingment.

Dean

There are two rotations to consider here. One is the torsion bar relative to the torsion housing splines and the other is the torsion bar relative to the spring plate splines. Both use slightly different spline offset to allow fine grained control of the angle and hence height.

Jon,

The main reason for taking your car to a Porsche-specialty shop for the alignment, is because a tire store may be able to measure the various settings on your car, but they will NOT have a clue how to adjust your rear suspension! So, if all you want is a report on where it is at, fine ... just don't expect the tire shop to admit they don't know how to adjust much of anything on your car! This is one case of ... 'you get what you pay for' ...

As far as the 'spline thing' goes ... there are 40 teeth on the inner part of the torsion bar, which means moving one tooth at the inner socket moves the torsion bar 9 degrees. There are 44 splines on the outer end of the torsion bar, which means moving the spring plate one notch moves it 8 degrees, 10 minutes, or 8.1818 degrees. So, a fine adjustment of 50 minutes of angle is possible by moving the torsion bar 1 notch, and the spring plate 1 notch, which changes the ride height approx. 6.5 mm, or a little more than 1/4". I suggest marking the end of the torsion bar, and the spring plates with a grease pencil before starting your adjustment procedure, so you can always get back to square one, if need be! An angle finder gauge is most helpful to determine spring plate declination angle!

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Warren Hall
1973 911S Targa