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Volkswagen Torsion Bar Indexing
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Lengthened Trailing Arms 
Reindexing Torsion Bar
You can advance your torsion bars to raise your suspension and likewise lower your suspension by reindexing the torsion bars in the other direction.
Note: Reindexing a torsion bar is more difficult and dangerous than the average DIY mechanic may be aware of. The spring plate is under tension and has enough force to break bones, amputate body parts of kill you if you put your head under the plate. This job should not be attempted by those not thoroughly familiar with all the safety precautions involved with this task.
The inner end of a VW torsion bar has 40 splines and the outer end has 44 splines. This allows to advance or retard the the torsion bar by 9° or 8.18° (or about 8° 11') respectively. By reindexing the inner splines one way and the outer splines in the opposite direction, you are able to make a net change of about 0.82° (or 0° 49') which will allow you to make small incremental adjustments to your height.
To change your ride height, you can mark your torsion bar and spring plate, make incremental adjustments until you your suspension angle seems correct (use a level protractor), duplicate that on the opposite side and take your VW for a test ride. If you want to predetermine how much to turn each end of your torsion bars, you can use the following chart, do the math yourself or use the calculator below.
Reindexing Changes of Rear VW Torsion Bar
Inner Spline  Outer Spline  Angle Change  Height Change (inch)  Height Change (CM) 
+ 1  – 1  0° 50'  0.22  0.55 
+ 2  – 2  1° 40'  0.43  1.10 
+ 3  – 3  2° 30'  0.65  1.65 
+ 4  – 4  3° 20'  0.87  2.20 
+ 5  – 5  4° 10'  1.08  2.75 
+ 6  – 6  5° 0'  1.30  3.30 
+ 7  – 7  5° 50'  1.52  3.85 
+ 8  – 8  6° 40'  1.73  4.40 
+ 9  – 9  7° 30'  1.95  4.95 
+ 10  – 10  8° 20'  2.17  5.50 
0  + 1  8° 10'  2.17  5.50 
+ 1  0  9° 0'  2.36  6.00 
+ 2  – 1  9° 50'  2.58  6.55 
+ 3  – 2  10° 40'  2.80  7.10 
+ 4  – 3  11° 30'  3.01  7.65 
+ 5  – 4  12° 20'  3.23  8.20 
+ 6  – 5  13° 10'  3.44  8.75 
+ 7  – 6  14° 0'  3.66  9.30 
+ 8  – 7  14° 50'  3.88  9.85 
+ 9  – 8  15° 40'  4.09  10.40 
+ 10  – 9  16° 30'  4.33  11.00 
+ 11  – 10  17° 20'  4.55  11.55 
0  + 2  16° 20'  4.33  11.00 
+ 2  0  18° 0'  4.72  12.00 
+ means that you are turning the torsion bar in the direction you would like to go Example 
Clockwise on rear right side to achieve increased ride height. 
What is the proper preload for your application? That all depends and there is even disagreement on what to do for a stock VW.
The stock VW Bug and Ghia torsion bar recommendations:
short swing axle  17° 30'  found on internet  Airhead Parts 
6768 long axle and IRS  20° +50'  found on internet  Airhead Parts 
Beetles  20° 20'  21° 10'  Rob and Dave’s Aircooled Volkswagen Web Pages 
IRS 70  21° 20' +50'  found in service manual  Bentley 
Sway Away Application Stock Preload Angle Recommendations:
Auto  Year  Length  Diameter  Preload Angle 
Bug  up to 1960  24 11/16”  24 mm  13 
Bug  19611968  21 ¾”  22 mm  16 1/2 
Bug  1969 & up  26 9/16”  22 mm  20 1/2 
Type 3  all  26 9/16”  23.5 mm  23 1/2 
Offroad preload recommendations:
48° greater than stock  
Swing axle  bottom edge of the spring plate is covering half of the bolt hole 
IRS 70 on  the spring plate is even with the bottom of the bolt hole 
Torsion Bar Position Math
Movement in Degrees per spline (inner) = 360°/(40 Splines) = 9° per spline
Movement in Degrees per spline (outer) = 360°/(44 Splines) = 8.18° per spline
Length of trailing arm (center of torsion bar to center of wheel hub)
Porsche 944 = 16.5"
73 Beetle ~ 16.5"
X = overall change in degrees of spring plate
Y = Length of the trailing arm
X_{1 }(includes X_{4}) = (tan X°)(Y)
X_{2 }(includes X_{3}) = Y/(cos X°)
X_{3} = X_{2 } Y
X_{4} = (sin X°)X_{3}
X_{4} = X_{1 } X_{4 }
Lift = (tan X°)(Y)  (sin X°) ((Y/(cosX°))Y) 
Lift/Drop Calculator
Number of Inner Spline Advance:  Inner Spline Count:  
Number of Outer Spline Advance:  Outer Spline Count:  
Trailing Arm Length:  Height Change:  
(a negative number means you
went in opposite direction than intended) 
Example 
CounterClockwise on rear right side to achieve increased ride height.
Example  Clockwise on rear right side to achieve
decreased ride height.
Example  Clockwise on left side to achieve
increased ride height.
Example  CounterClockwise on left side
to achieve decreased ride height.
– means that you are turning the torsion bar away from the
direction you would like to go
Achieving a Half Increment
For VW torsion bars with 44 and 40 splines, you are able to achieve small incremental degree changes by changing the the inner end by one spline and turning the outer end in the opposite direction by one spline. This method will give you reasonable results and easily get you in the range of where you would like to be. If you would like to achieve a final angle that is in between two measured angles achieved by this adjustment method, you will need to turn the entire torsion bar about 45 degrees (either direction), realign the spring plate and adjust as necessary from there.
Since the 40 and 44 ends will match at every 90 degrees, turning your torsion bar exactly 90 or 180 degrees in either direction should give you the same angle as you have currently.
Preload Adjusters
These are made for the front and rears of VWs. Center ones allow for fine adjustment of ride height without removal of the torsion bars, but require cutting and welding of the torsion housings. Adjustable spring plates are much simpler to install and a snap to adjust, but add a small amount to the total amount of unsprung weight. Both allow you to fine tune you suspension for different terrain or more commonly  for a different street look.
Ref:
Torsion Bar Size
VW autos commonly use one of three different rear torsion bar lenghths.
Size  Length  Application 
Short  213/4"  6068 Swing 
Intermediate  2411/16"  4959 Swing 6972 T1 IRS 6567 T3 Swing 
Long  269/16"  73up T1 IRS 
The longer and the thinker the diameter of a torsion bar, the softer the ride. The shorter and the thicker the diameter of a torsion bar, the firmer the ride.
Lighter weight fiberglass bodied buggies may benefit from narrower diameter bars and heavier offroad creations may benefit from wider diameter torsion bars and more preload.
Depending on the weight and purpose of your VW, you may opt for other than stock torsion bars. In the past, VW offoaders have switched to shorter rear torsion bars to allow of larger tires in the rear. The sorter torsion bars unfortunately lead to a harsher ride and there are other ways of allowing for larger tires that more commonly used these days.
Recommendations by Baja Bugs and Buggies
Vehicle  Bar diameter (mm)  Preload 
1,400lb Single Seat buggy  25, 26, 27  710° 
1,700lb Two Seat buggy  26, 27, 28  811° 
2,000lb Baja Bug or Sedan  28, 29, 30  912° 
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