Torsion Bars – Removing, Replacing, and Indexing – 2.5L NA

Overview

This procedure guides you through removing, replacing, and indexing the torsion bars on all Porsche 944  variants with an 8-valve engine configuration. Torsion bars control the rear suspension’s ride height and stiffness, and this process is typically performed to adjust ride height or upgrade to stiffer bars. Proper execution ensures optimal suspension performance and vehicle handling. This guide is tailored for pre-1985.5 (83-85.5) and 1985.5 onwards (86-88) models, with model-specific steps clearly marked.

Pink and blue text represent links to additional resources, tools, parts, and partner websites.

Tools Required

• Jack stands
• Floor jack
• Metric socket set (including 13mm, 17mm, 19mm)
• Metric combination wrench set (including 13mm (1/2 inch), 17mm (11/16 inch), 19mm (3/4 inch))
• Pry bar
• Measuring tape or ruler
• Marker or scribe for marking measurements
• Heavy-duty strap (e.g., ratchet strap)
• Bungie cords or wire for securing axles
• Material to fabricate a measuring device (e.g., flat metal or sturdy cardboard)

Parts Required

• Torsion bars (if replacing, size varies; e.g., 944 333 031 00 for 25.5mm or 944 333 032 00 for 30mm)

Required Additional Procedures

Steps in these procedures are required to complete this process:

• Rear Sway Bar Removal and Installation

Step-by-Step Procedure

Step 1: Measure Initial Ride Height

1. Park the vehicle on a level surface.
2. Measure the ride height from the ground to the top-center of the rear fender well, centered on the wheel. Aim for approximately 25 inches (63.5 cm) for optimal balance. Record this measurement for reference.

Step 2: Prepare the Vehicle

3. Raise the rear of the vehicle using a floor jack and secure it on jack stands.
4. Follow this link to ensure this step – Rear Sway Bar Removal and Installation – of the process is followed accurately to remove the rear sway bar and drop links.
5. Lower the vehicle back to the ground.
6. Bounce the rear of the vehicle several times to settle the suspension.

Step 3: Fabricate and Use a Measuring Device

7. Fabricate a measuring device (e.g., from flat metal or sturdy cardboard) with two holes matching the bottom two bolts of the torsion tube chassis mount (end cap) for reference.

8. With the vehicle on the ground, attach the measuring device to the end cap. Measure and mark the height of the spring plate relative to the end cap. This is the loaded spring plate height. Note: This may be awkward with the wheel in place.

Step 4: Remove Suspension Components

9. Raise the rear of the vehicle and secure it on jack stands.
10. Remove the rear wheels using a 19mm (3/4 inch) socket.
11. Unload the torsion bar by removing the bottom rear bolt (M10, 17mm (11/16 inch) head) on the torsion bar chassis mount (end cap).

For Pre-85.5 models:

• Use a 17mm (11/16 inch) wrench to remove the bolt, as it may differ slightly in size or threading.

For 85.5 Onwards models:

• Ensure the bolt is M10 standard; a 17mm (11/16 inch) wrench should fit securely.

12. If installing new torsion bars, use the measuring device to mark the spring plate’s unloaded position relative to the end cap.

13. Disconnect the rear brake lines at the calipers using a 13mm (1/2 inch) wrench.
14. Unplug the brake pad wear sensors by gently pulling the connectors.
15. Unbolt both rear axles from their trailing arms using a 19mm (3/4 inch) socket and hang them out of the way with bungie cords or wire.
16. Remove the bolt attaching the trailing arm to the torsion tube (M12, 19mm (3/4 inch) head).
17. Support the trailing arms from the transmission crossmember using a heavy-duty strap to prevent damage or injury.
18. Remove the three nuts and bolts holding the trailing arm to the spring plate (M10, 17mm (11/16 inch) heads). Note that the rear two bolts are eccentric bolts for height adjustment. Tap the eccentric bolts gently with a hammer to free them if stuck.
19. Remove the nut and bolt holding the torsion tube cantilever arm to the chassis mount near the top of the wheel well (M10, 17mm (11/16 inch) head).

Step 5: Remove the Torsion Tube Assembly

20. Place a floor jack under the center of the torsion tube assembly and raise it until it just contacts the tube.
21. Remove the nut and bolt attaching the torsion tube chassis mount to the vehicle body (M12, 19mm (3/4 inch) head).

22. Gently pry the torsion tube assembly free from the body, alternating sides, and lower it using the floor jack.
23. Remove the three remaining bolts (M10, 17mm (11/16 inch) heads) in the torsion tube chassis mount.
24. Remove the torsion tube chassis mount and spring plate.
25. Pull the torsion bar out of the torsion tube.

Step 6: Replace the Torsion Bar

26. Measure the loaded-to-unloaded range on the measuring device (distance between the loaded and unloaded marks from removal).

27. If replacing with a hollow torsion bar, note the manufacturer’s equivalent solid bar diameter (e.g., a 30mm hollow bar may equate to a 25.5mm solid bar).
28. Calculate the new torsion bar’s loaded-to-unloaded range using the formula: New Range = Old Range × (Old Bar Diameter / New Bar Diameter)⁴. For example, upgrading from 25.5mm to 30mm with an old range of 50mm: New Range = 50 × (25.5 / 30)⁴ ≈ 30.6mm.
29. Measure the new range down from the loaded mark on the measuring device and mark the new unloaded position.
30. Install the new torsion bar (944 333 032 00 for 30mm, or as specified) into the torsion tube.
31. Install the spring plate and torsion tube end cap, aligning the spring plate to the new unloaded position using the measuring device.
32. Secure the end cap with at least two bolts (M10, 17mm (11/16 inch) heads).

Step 7: Reinstall the Torsion Tube Assembly

33. Raise the torsion tube assembly into position using the floor jack.
34. Bolt the trailing arms to the spring plates, ensuring the eccentric adjusting bolt is centered (M10, 17mm (11/16 inch) heads).
35. Bolt the trailing arm to the torsion tube (M12, 19mm (3/4 inch) head).
36. Attach the torsion tube cantilever arm to the chassis mount near the wheel well (M10, 17mm (11/16 inch) head).
37. Attach the torsion tube chassis mount to the chassis (M12, 19mm (3/4 inch) head).

Step 8: Check and Adjust Ride Height

38. Remove the vehicle from the jack stands and bounce the rear end several times to settle the suspension.
39. Measure the ride height again, comparing it to the target of 25 inches (63.5 cm).
40. If the ride height is within ±0.5 inches (1.3 cm), adjust the eccentric bolt on the spring plate using a 17mm (11/16 inch) wrench to fine-tune the height.
41. If the adjustment needed is greater than 0.5 inches (1.3 cm), lower the torsion tube assembly and reindex the torsion bars (see Step 9).

Step 9: Index the Torsion Bars

42. Understand that the torsion bar has 40 inner splines (9° per spline) and 44 outer splines (8.18° per spline). Moving one spline adjusts ride height significantly.
43. Calculate ride height change per spline: For inner splines, one spline lowers the ride height by approximately 2.58 inches (6.6 cm); for outer splines, by 2.35 inches (6 cm).
44. To adjust, unbolt the torsion tube assembly and rotate the torsion bar one spline at a time:

    For lowering ride height:

    • Rotate the inner end counter-clockwise one spline while keeping the outer end fixed.

    For raising ride height:

    • Rotate the outer end (spring plate and chassis mount) clockwise one spline while keeping the inner end fixed.

45. Reinstall the torsion tube assembly and check ride height. Repeat reindexing as needed (multiple attempts are common).

Step 10: Complete Reassembly

46. Install any remaining bolts in the torsion tube end caps (M10, 17mm (11/16 inch) heads, tighten to 46 Nm (34 ft-lbs)).
47. Follow this link to ensure this step – Rear Sway Bar Removal and Installation – of the process is followed accurately to reinstall the rear sway bar.
48. Reconnect the brake lines to the calipers (tighten to 15 Nm (11 ft-lbs)) and plug in the brake pad wear sensors.
49. Reinstall the rear axles to the trailing arms (tighten to 85 Nm (63 ft-lbs)).
50. Install the rear wheels (tighten to 130 Nm (96 ft-lbs)).
51. Lower the vehicle and bounce the rear end to settle the suspension.
52. Recheck ride height after a few days to ensure it remains at 25 inches (63.5 cm), as settling may occur.

Post Procedure Checklist

• Verify ride height is approximately 25 inches (63.5 cm) at the fender well.
• Check all bolts for proper torque (e.g., end cap bolts at 46 Nm (34 ft-lbs)).
• Ensure brake lines are secure with no leaks.
• Confirm brake pad wear sensors are properly connected.
• Test drive the vehicle for 5 miles (8 km) to check for unusual noises or handling issues.

Sources

• Clark’s Garage
• Pelican Parts
• Porsche 944 Workshop Manuals
• YouTube