Torsion Bar Indexing Thread?

[Jim2]

Could somebody point me to a thread about indexing torsion bars for specific ride height adjustment? I've seen one or more threads in the past but I'm unable to locate them now.

Thx.

1970 911, non adjustable spring plates.

[BFT3.2]

Im sure this will help a little, it got me within a 1/2" of where I wanted to be, 1/2 lower to be precise.

Spring Plate angle calculator:
911 Spring Plate Angle Calculator

[Jerome74911S]

That's useful, but how about the front of the car? How does it come apart, and how do you do the re-index?

[Jim2]

Jerome, the front end on 911s are all adjustable, and if the adjusting bolt is out of range it's easy to pull the end cap off the torsion bar by removing the adjusting bolt then sliding the end cap back on clocked to a different spline, then screw the bolt back in.

The rear is the bugger on the old 911s without adjustable spring plates. I'm keeping this car stock so not wanting to install the later spring plates.

BFT, I found that calculator by Will but I seem to recall another one where it gave # of degrees per outer spline, along with computation for counter rotating inner spline. This ring a bell?

[BFT3.2]

Jim, yes it all rings a bell now. When I did mine I did in fact have a cheat sheet of degrees per outer and inner spline and estimated change in height per notch. Im near positive that I didn't find it in a calculator specific to the splines, not that it doesn't exist though.

[brianlay]

This is the data for Carreras from my Bentley manual. I'm not sure if the number of splines is the same for the the earlier cars, but I think it is.



The method I've used is:

Measure current ride height and calculate how much change you want on each rear wheel, keeping in mind the minimum change that's achievable. (That's why adjustable plates are desirable)

Jack up the car and disconnect everything from the torsion plate and let it droop down.

Measure the angle of the plate and then calculate what the new angle should be, based on the desired height change.

Pull out the torsion plate and adjust the inner and outer torsion bar splines as necessary to get the desired angle.

Bolt everything back together and you should be all set. If you want check before putting everything together, attach the wheel hub on the torsion arm (don't bother with attaching the shocks or the torsion plate covers), lower the car onto the wheels, and confirm the new ride height.

I've used this method, and even changing torsion bar sizes only requires one extra step.

This method reduces the trial and error that a lot of folks talk about.

[BFT3.2]

^^^^Thats the one!

[Jim2]

Thanks Brian, this is likely what I had seen in another thread which I recall from long ago.

Should have me going on Friday or Saturday

[Bobboloo]

I've done this many times. It's the different ratio between inner and outer splines that makes it work. i.e. you can't just re-adjust by using either inner or outer spline. (you can't leave the torsion bar stuck in the spring plate or the the torsion bar stuck in the torsion tube both must be separated)

I pick a rotation direction for each. In other words torsion bar clockwise, spring plate counterclockwise. The key here is to make sure the inner spline only goes one direction the outer is easy because when you're putting on the spring plate it'll be obvious where it needs to go.

[Jim2]

Done and worked perfectly guys, thank you!

Based on the table above:

40 splines on inner end = 9 degrees per spline

44 splines on outer end = 8.2 degrees per spline

rotate bar one spline while rotating spring plate one spline in opposite direction results in .8 degrees rotation or approx .256" at the wheel.

I noted angle of spring plate, then removed it.

Put vice grips on T-bar and noted angle, this way I could be certain that I got the bar where it needed to go back in.

I'll get off my butt this aft and finish up the alignment and finally drive this thing.