993 Driveline Information
The 993 C4, C4S and Twin Turbo all had torque tubes installed to transmit power to the front wheels for a four wheel drive configuration as the previous 964 C4 variant. The 993 torque tube was designed and manufactured to a higher tolerance and weighs considerably less than the 964 torque tube.
The 993 torque tube also houses a lighter drive shaft which is hollow. It has an internal spline at the front and a splined shaft which is welded into the hollow drive shaft at the rear. The splined shaft portion interfaces with the transmission input shaft via a coupler of a different design than the 964 torque tube.
The hollow drive shaft did add lightness to the torque tube assembly, but at a cost. The rear splined shaft tends to shear along the weld and there have been instances when the driver notices a cessation of four wheel drive during spirited driving, especially in inclement weather. Suspicion is usually focused on the front differential as being the culprit which is summarily replaced. Unfortunately four wheel drive is not restored and further diagnostics are performed until the fractured spline shaft is found.
As can be seen above, the splined shaft weld is broken and power is no longer transmitted to the front wheels. The broken shaft instead spins inside the hollow drive shaft and is usually hard to detect. Besides the loss of power to the front wheels, no other significant noises or other telltale signs are present to help diagnose this failure. As can be seen in the bottom picture, the splined shaft has a short stub which enters into the hollow drive shaft with no other mechanical means of securing the two parts together other than a thin weld.
The Black Sea R&D Fix
As long as the hollow drive shaft is not worn too much or damaged, we have developed a fix for this problem. We engineered a new splined shaft with a longer stub shaft which is mechanically captured within the hollow drive shaft. No welding is used since to further heat the affected area could cause the hollow drive shaft to become brittle and fail again. The fixed 993 hollow drive shaft is above the original broken splined shaft.
This fix was used on a modified European spec yellow 993 twin turbo said to be producing approximately 700 RWHP. The owner advised he had noticed a loss of his four wheel drive as he powered around his favorite corner one day. After spending a lot of time and money changing out the front differential with an uprated one which did not fix the problem, his technicians found the broken rear drive shaft. We sent his technicians our rebuilt 993 torque tube with our 993 Super Bearings and our fixed drive shaft. After installation the owner reported that all was good and he was enjoying his four wheel drive again in his 993 twin turbo. Pictures below are of his vehicle on the lift, a picture showing the torque tube with the broken drive shaft as it waits to be removed and a picture of his technician holding the broken splined stub shaft taken out of this Porsche.
We have since repaired more broken 993 drive shafts and it seems to be a problem that is not well known amongst the 993 community. Our repair should be considered before purchasing a rebuilt 993 torque tube from other vendors to include Porsche, since the drive shaft design itself is the problem
Price for 993 Drive Shaft repair and enhancement: $500.00
Note: Not all damaged 993 drive shafts are repairable. Damaged 993 drive shafts must be inspected by us to discern viability of repairing them.