71T Ride Height

[TommyV]

I've finally got my project car on the road. I took it for inspection yesterday and need to solve a couple little things. Who knew that you needed 2 working seat belts if you only have one seat? I need a seat support rail on the passenger side before I can mount that seat. PM me if you have one!

My ride height is a little low at the front, I was at 25" on the pass side and 23.5 on the driver at the front wheel well. Stock fenders all the way around. I tried measuring from the center line of the wheel and the center line of the torsion bar and taking the difference and even after getting both sides to 25.5", I was getting a difference of over 140mm! Euro ride height as best I can figure it is 108mm. It looks ok now and I'm satisfied, but the 140mm number baffles me!

At the rear, I'm at 23.5" at both wheel wells. I know I need to re-index the spring plates. I found a video on line that speaks to the 40 spline inner and 44 spline outer on the torsion bars and that if you go 1 spline on each in opposite directions you get abut 1.1 degrees of angle change on the spring plate. Here is the question: How much ride height does that translate to? I need to come up about 1.5". I'm doing this on the garage floor and my body will be very thankful if I can do it once and get it right.

Here's the video I watched:https://www.youtube.com/watch?v=GqBw1kMJ_d8

In his second video, he says it's strictly trial and error, but I figured someone on here was smart enough to know how to calc the height based on the angle change.

[Richy]

Actually 1 spline each opposite is 50 minutes . 50 minutes is about a 7mm change in ride height . 1.5 "= 37mm . 37 divided by 7 = 5.28 . So turn the inside splines 5 "clicks " to increase the springplate angle and the outside 5 opposite . 50 minutes = .8333 degrees X 5 = 4.16 degree change .

[TommyV]

Thanks for the reply Richy!

OK, so 360 degrees/40 splines = 9 degrees per spline on inner
360/44 = 8.18 per spline on outer

9 - 8.18 = .818182
.818182 x 60 (min per degree) = 49.09 min.

As you said about 50 min.

How did you determine that 50 min = 7 mm change in ride height? I have no reference, but 4.16 degree change in the spring plates seems pretty big.

[TommyV]

So I went to the spring plate the Spring Plate Calculator page : http://rennlight.com/cgi-bin/spring.cgi

I put in my weight ~ 2300 lbs and rear T-Bars = 26mm and for Euro ride height ~ 25" at rear fender it said spring plate angle should be 25-26. For US ride height ~ 26" is said 28-29 degrees. So 1" in ride height should be ~ 3 degrees in spring plate angle change. Given that, 4.16 sounds pretty darn close for a 1.5" change in ride height. Great info Richy!

Thanks for listening!

[Richy]

The 50" = 7mm value is in the little technical specifications book for '76 '77 911 . I find that this equation works for our earlier cars .

[TommyV]

Richy, I always forget the wealth of info in that little book. I've got one for my 71. I went home last night and prepared to take the suspension apart to re-index the T Bars. In the process I decided to see how far my later adjustable spring plates would go and they surprised me by going from 23.5" at the fender lip to over 26" at full adjustment of the eccentric. I'm looking for 25" at the fender, so my project just shrunk considerably. I'm happy!! I adjusted the front and back and it was interesting that even minor adjustments on one corner would effect the other side quite a bit and even the other end to some extent. I'm not done, but I'm close at 25.25" and 25" at the front and after a couple iterations I'm at 24.5" and 25.25" at the back. Also, after setting the height and bouncing the car I thought I knew where the height was. Then I took it for a drive and it settled over 3/4"! I'll dive back in tonight and get it done.

Tom