944 Driveline Information
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944 Drive Shaft Problems
We are noticing many 944 torque tubes coming in for rebuilds with damaged or worn out drive shafts that make them unusable for rebuilds and unacceptable for cores. Most of the problems are with the front nub of the 944 drive shaft that fits into the pilot bearing at the back of the crank shaft. This holds the drive shaft in place and keeps the drive shaft from vibrating under operation within the clutch. Pronounced vibrations will damage clutches and the drive shaft so this is a very important area to make sure it is within specifications. The easiest method is to take a pilot bearing and fit it on the nub. The fit should be snug with no looseness. The looser it feels the more the drive shaft will vibrate.
This picture shows three 944 drive shafts. The bottom one was still a snug fit and was acceptable for rebuilding. The middle one was loose and not acceptable, a fact which could not visually be determined. The top drive shaft is extremely out of specification which can be easily seen.
It is very important that the pilot bearing at the back of the crank shaft be changed with every 944 torque tube R&R. Not doing so will result in damaging the drive shaft nub which can cause further damage to the 944 drive line.
944S2 and early 968 Split Torque Tube Problems
We have found that 944S2 and early 968 "split" torque tubes have problems with keeping the front bearing unit in place. This is due to the split widening and letting the front bearing unit spin around with the drive shaft. It then gets caught at an odd angle to the drive shaft and comes apart. This will cause a vibration to be felt while driving and could possibly damage the drive shaft. The split also allows more debris and water to migrate into the torque tube which also hastens the damage to the bearings within it.
Below is a picture showing the split which is located on the bottom of the torque tube as it sits in the car. It extends from the front of the torque tube to the shifter mounting point. This split is usually covered by silver duct tape from the factory.
The picture below shows a customer's 944S2 torque tube that came in for a rebuild. The picture was taken through the split and shows the front bearing insert had delaminated from the metal substrate which is still in the bearing. The thin rubber is on the drive shaft.
The next picture shows this same bearing unit out of the torque tube where the delamination of the bearing insert can be more easily seen.
The delamination of the front bearing insert caused some damage to the drive shaft seen in the pictures below. The coating Porsche put on the 944S2 and 968 drive shafts for extra protection due to the split design has been worn off which allowed rust to start migrating under this coating.
Black Sea R&D modification efforts and current policy on split torque tubes
We initially tried to pin our 944 Super Bearing within the split area and thought we had done a good job. Unfortunately the 944 Super Bearing was pinned at an angle and came apart in the exact same way as the original bearing insert.
We then tried another solution with limited success due to the difficulty of securing the front bearing unit exactly in the middle of the torque tube to allow the proper running of the drive shaft without any pre-load due to angulation. This is due to a sliver of metal actually having been removed from the torque tube during the splitting process.
Due to these problems and liability concerns of modifying split torque tubes, Black Sea R&D will no longer offer rebuild services for these torque tubes.
944S2 and 968 owners have the option of replacing their split torque tubes with a 944 and 968 torque tube that does not have the split. 944S2 owners should ensure the replacement torque tubes have the safety hooks on them since these were placed on the torque tubes to keep the drive line assemblies from moving during a crash.
924-944-968 V-8 Engine Conversion Drive Shaft Problems
We have noticed some V-8 engine conversions have problems with their torque tubes due to the drive shaft being improperly spaced in the clutch assembly. This improper spacing ruins the drive shaft.
Below are photographs of a ruined drive shaft end nub and splines due to this type of improper spacing. You can see where the clutch was riding at the end of the splined area instead of engaging the middle portion of the drive shaft splines. This misalignment finally caused a failure of the torque tube bearings, which had previously been rebuilt with inferior bearings and aftermarket hard plastic inserts, which then caused drive line vibrations during operation. If you see this type of failure you will need to obtain proper spacing between the flywheel and clutch assemblies, as well as a new pilot bearing housing to correctly capture the drive shaft end nub. These parts can be obtained from different aftermarket sources which can be located by visiting the 944 Hybrids Forum online.