Spring Plate Indexing Calculator

[Superman]

Somebody has calculated and posted a method of calculating the angle to use in attaching the spring plate to the rear torsion bars. I am told this calculation works well, and I'm thinking of re-indexing my spring plates (the car rides WAY too high and the fine adjustment is maxed). Plus, I should probably replace the spring plate bushings.

Anybody know who created this calculation and where to find it?

[widebody911]

At your service:

http://rennlight.com/cgi-bin/spring.cgi

[Superman]

Thanks, Thom. My car is an '83 SC with obviously stock rear torsion bars. They're 26mm aren't they?

[juanbenae]

24 on a stock sc.

[widebody911]

IIRC, 930's had 26mm

[Superman]

Thanks, Toby.

[Superman]

So lemme get this straight. If the calculator says 30-31 degrees, this means that when the car is on jackstands, the spring plates should be set 30-31 degrees from horizontal? With "horizontal" meaning the angle of the rocker panels?

[BK911]

I know this isn't what you asked, but maybe somebody else will find this helpful.

I did mine a little different. I set my spring plates about half way. Then I measured my fender height. I wanted to raise my car 1". So I put the car on jack stands and disconnected the spring plate from the trailing arm so the spring plate was free. Then I measured the distance from the floor to a point at the end of the spring plate. The point I measured on the spring plate was approx. 3/4 of the way from the t-bar to the rear axle. So multiplied 1" x 3/4 to get 3/4". So I indexed the t-bar until the same point on the spring plate was 3/4" lower than my initial measurement. Worked perfectly and I didn't have to touch the spring plate adjustment.

I hope this made sense.

[juanbenae]

sup, you gotta add or subtract the angle of the car as it sit on the stands. i forget which it is, but if it says 31* that is 31 from level. i am pretty sure you subtract.

figure out the angle of the car, i used the doorsil, say it sits at 6* while on jackstands, you will subtract the 6 from the 31 and you should set it at 25* from level. i think there is a good section on that in the bently. i used a smart level (not a smart racing tool, but a 2 ft level with degress and %) not the dial and bubble recommended in waynes 101 and bently.

[widebody911]

Originally posted by Superman
So lemme get this straight. If the calculator says 30-31 degrees, this means that when the car is on jackstands, the spring plates should be set 30-31 degrees from horizontal? With "horizontal" meaning the angle of the rocker panels?

Correct - that's with the car level and the spring plate hanging free on the torsion bar, separated from the trailing arm.

It's a good idea to center your spring plate adjusters at the same time, so you'll have that ace in the hole should you need it at a later date to fine-tune your ride height and/or corner balance.

[Superman]

I got it. Thanks, dudes.