One spline = ? inch in height

[Brorag]

I've searched but can't find the thread with the discussion about the approximate change in height when one ratchets a torsion bar 1 notch.
Inner and outer torsion bar spline counts are different, so combinations of the two give different height results. Help an old f*rt out--I'm fading fast.......................

[dad911]

Spring Plate and Torsion Bar Installation - Indexing

Need to know torsion bar diameter, and weight of car.

[will hung]

Brorag, here you go.

Reindexing rear torsion bars?

From the link:
"...1 degree of spring strut inclination = approximately 7-9 mm change in car height, so 9 degrees would be in the neighborhood of 63-81 mm ride height change. 3" is around 76 mm, which is right in that range."

[Flieger]

I believe the splines are 40 outer and 44 inner, which would mean a minimum adjustment increment of 0.818181... degrees. Combine those degrees with the change in height per degree from the calculator and there you go.

[Hodgey]

One notch on the inner (40 spline) is approximately 6-8 mm difference in height

[Brorag]

To all who have responded, thank you!

Here's the next question.............

I detected in some of the responses what appeared to be some different #'s , so I went to the referenced part of Haynes (pp 420-11/420-16).

For my car, an '87 Carrera, the specs are:

• torsion bar diameter--25 mm
• torsion bar splines inside/outside--46/47
• torsion plate inclination--32 degrees

First, I place some weight compensation on the drivers side for the drivers weight, and have the fuel tank at 3/4 full, and normal trunk load. Given my weight is a svelte 280 lb, I add 7 bags of rock salt@40lb ea to compensate for my avoirdupois (a.k.a., typical american lard a*s).

Using Hodgy's guideline of 1 notch of the inner 40/44 spline torsion bar (the 40 spline end) yields 6-8mm (7mm for this calculation) change, I can infer that 1 notch of my inner bar equals approx 8mm change (40/46=7/X; 40X=322; X=8mm).

So, if I want to raise (or lower) the rear of the car by 20mm, I move the inner part of the torsion bar by 2.5 splines. Can't do that, so I adjust 3 splines and set the spring bar adjustment to max up or down, depending if I'm going up or down, then move the spring adjust to fine tune the height.

Does this pass the test of reason?

[Flieger]

I missed the part about this being a G50 car. Those bars are different.

[Brorag]

Bill K
thanks--important point

[qikcpa]

i read in another post about measuring the height from the lowest part of the spring plate to the ground (say 12 inches). if you want to raise your car .5 inch then rotate the end of the springplate so that the lowest point is .5 inch lower (11.5 inches to the ground). this is all done with the spring plate disconnected from everything (basically just hanging there by the torsion bar). if you have a nice flat garage floor and the car is evenly raised you can make sure that both sides are the same distance to the ground (ie 11.5 inches) to balance the sides.

worked for me. ymmv

[qikcpa]

Originally Posted by bkreigsr

only valid if you assume the torsion bar (aka spring) is not going to twist once it is supporting the weight of the car. Bill K

of course it will twist, but keep in mind its a relative change of .5 inch. you cant say "i want to have 24.25 fender height...but you can say if my car is 24.75 now and i want to lower it half an inch, i can raise the height of the end of the unsprung spring plate by half an inch (from the ground) and that will get me very close.

i guess if you wanted to be exact you could extend the springplate to a vertical that would go through the axle/center of the wheel and use that extended length to measure/make the adjustment...if my 7th grade geometry is correct.


(when i say extend the springplate i mean to tape/clamp a straight edge or stick or something to it to make it longer)

[Brorag]

Bill K, do you recall about how much difference one notch made when you put the car back on the ground?
Flieger, not to worry. I'm constantly amazed at the infinate varibility of these cars.....were any two built alike?

[Brorag]

Bill K,
Exactly what I'm looking for--gotta go back up--dragging the expensive end over bumps.

[Flieger]

I have the SC spring plates on my '71 but the adjustable plates can only adjust so much.

[Brorag]

wish I had a new bff...................

[Brorag]

Per Bruce Anderson in his Performance Handbook:

Adjusting Rear Torsion Bars

Old Version 44/40 teeth
• Adjusting the torsion bar one inside tooth up and the swingarm one tooth down produces a swingarm change of approximately 50 min and a vehicle height change of approximately 6.5 mm.
• If the torsion bar is turned one tooth on the inside, the adjustment is equal to 9 deg.
• If the spring strut is turned one tooth the adjustment is equal to 8 deg 10 min.

New Version 47/46 teeth
(1987-89 and 1989 Turbo)
• Adjusting the torsion bar one inside tooth up and the swingarm one tooth down produces a swingarm change of approximately 10 min and a vehicle height change of approximately 1.4 mm.
• If the torsion bar is turned one tooth on the inside, the adjustment is equal to 7 deg 50 min.
• If the spring strut is turned one tooth, the adjustment is equal to 7 deg 14 min.

If you use stiffer-than-stock torsion bars, you will be able to lower the 911 about 1 inch without suspension travel problems, but you may have to modify the alignment slots to facilitate a proper alignment and you will have to be very careful going in and out of driveways. A lower ride height will reduce roll and lower the center of gravity, which will improve the 911's cornering power and make it smoother in the corners.

[88911coupe]

For some reason I can't seem to get it clear in my head how I'd make a change of, say 2.5 degrees more droop. This is what I was wrestling with recently when I needed to get it somewhere between the tooth setting on my ''88. 360/46 = about 7.8 degrees and 360/47 = about 1.7...correct? If, for example, I need to drop the spring plate 2,5 more degrees what combination of inner/outer tooth movements would provide this result? I was trying all sorts of combinations and it seemed to stay the same amount of degrees "off" no matter what I did. Finally I took it off and used the adjustment function but that's not really practical for me since I don't have a thin wrench and the whole plate has to be moved and I do the guessing game again on how far to move it. I'd like to get it really close just adjusting the teeth but maybe that won't work...am I missing something?

TIA

[jstobo]

Just subtract. Move inner one spline down= -7deg 50 min. Outer up one spline means +7deg14min. So you get a -36min move. To get 2.5 deg =150 min divide by 36 and you get about 4 splines. So go down on the inner 4 splines and up on the outer 4 splines and you get -2.4 degree drop. Hope this is clear. Good luck.

[88911coupe]

Thanks, that makes it much clearer!

[88911coupe]

May be a stupid question but I'm not following the math that results in the outer being 7 degrees, 14 minutes per tooth change. On the other hand I'm getting 7 degrees, 50 minutes on the inner. Slow math skills kicking in here...

[jstobo]

You are right on the math. I just used the numbers in the previous post. 360/46=7.826 deg
360/47=7.659 deg or about 10 min difference. So just use that difference when turning the splines. 2.5 deg=150 min so you must turn the splines 15 in opposite directions.