Rear Torsion Bars

[A.T.]

I'm right in the middle of having the suspension reassembled on my '69S. We were going to go from the stock 23mm rear torsion bars up to 25mm. My mechanic sourced a set of used 25s but ran into a fit problem. If I understood him correctly he thinks the 25s are the same size (diameter) spline at either end but that the 23s out of my car are thicker at the outer end and thinner at the inner end. Does this sound accurate? I spoke with Al at Parts Heaven. He seems convinced that all rear torsion bars should be the same fit from '65 to '86. I'd hate to order a set from him and have my mechanic say I told you so.

Can anyone clarify this for me?

Thank you.

P.S. Here's hoping this is the last hurdle before I get this thing back on the road.

[mike walker]

I had a similiar question, here was the answer on my thread

http://www.early911sregistry.org/for...ad.php?t=10500

[A.T.]

Thanks, Mike.

Our confusion is really about the fit and spline size at the opposite ends of the rear T bars on a '69. I'm sure this is a total beginner question. Hope someone can shed some light.

[Eric911S]

A.T. : All of the torsion bars from 69-84 will fit. The splines are different end to end. There is 1 less spline on the inner side. If you get torsion bars from a SC you will have a great street setup with a soft ride. I like 26 or 27 rear bars for a street track car like I told you before. You can get some used 911 Turbo torsion bars that will work. I would also check if there is rust blocking the torsion bar from going in the splined holes. Lastly make sure you don't have 87 torsion bars as they are longer and have larger splines. Good luck. Thanks Eric

[ttweed]

The splines are different end to end. There is 1 less spline on the inner side.

Actually, there are 40 teeth on the inside splines and 44 on the outside on the early bars ('65-86,) a difference of 4 teeth, not one. It's the G50 bars ('87-89) that have the one tooth difference (47/46 teeth.) Having just today put 26mm bars in the rear of my '68, I can tell you with certainty that they are quite different in diameter at the two ends. A one tooth adjustment on the inside splines makes for an 8 degree adjustment in springplate angle. A one tooth adjustment on the outside splines is almost 9 degrees. Going up one inside tooth and down one outside tooth (or vice versa) at the same time is how fine adjustments are made (about 1 degree or 6.5mm in ride height.)

BTW, I found Wil Ferch's angle calculator to be spot on in predicting the change in my springplate angle. I hit the 24.5" ride height that I wanted in the rear on the first try at indexing the bars. See http://rennlight.com/cgi-bin/spring.cgi if you need to do this.

TT

[Eric911S]

Hello: I stand corrected, since I have not actually counted the splines on the bars then the above info is correct. Thanks Eric

[A.T.]

Thank you, Tom. Thanks again, Eric. I think we got it figured out now. The 25 mm T bars we found were definitely the wrong spline size for my car. My mechanic found a nice set of 24s with the proper fit. He is setting me up with a softer ride for now, 19 front/ 24 rear, but with a stiffer shock and antisway bar set up. Almost everybody who had an opinion here on the forum was leaning toward thicker T bars for a road/track application. I bugged my guy about it enough times that he finally said, "Look. If these aren't stiff enough I'll reinstall heavier ones. Okay?" I'm really looking forward to getting acquainted with the new set up soon.

Thanks again.