928 Driveline Information
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928 5-speed Drive Shafts
All 928 5-Speeds have 25mm drive shafts in their torque tube regardless of model year.
928 Automatic Drive Shaft Differences
The 928 automatics have two different sized drive shafts according to model year. From 1977 through 1986 the 928 had a 25mm drive shaft installed in the torque tube. Sometime in 1987 Porsche changed it to a 28mm drive shaft. However they kept the splined areas of the drive shaft at 25mm which necessitated the drive shaft to be necked down. This neck down has been found to be a shear point for the 28mm drive shafts which will be discussed below.
We have had problems with customers who have ordered our 928 torque tube rebuild kit for a certain model year only to discover the wrong size drive shaft is in their 928. This is usually due to the prior owner replacing the torque tube with one from a different model year. Both the 25mm and 28mm automatic drive shafts will fit all model year automatic 928s. Below are a few pictures to help distinguish which drive shaft you have in your 928.
The picture below shows the engine end of the 25mm automatic drive shaft on top and the 28mm automatic drive shaft on the bottom. Notice the pronounced necked down area of the 28mm drive shaft after the splines.
The picture below shows the transmission end of the 25mm automatic drive shaft on top and 28mm drive shaft below.
Drive Shaft Problems
We have many drive shafts coming in for rebuilds or being sent back as cores with damaged drive shafts. Below are a few pictures of different types of drive shaft problems and what to look for before sending in your 928 torque tube for rebuilding or as a core. We will not rebuild your torque tube with a damaged drive shaft due to warranty concerns. We will not refund your total core charge if the drive shaft is damaged.
The picture below shows damage to the rear splines of a 928 5 speed drive shaft rendering it unusable for a rebuild.
The picture below shows the engine end of two 928 5-speed drive shafts. The one on top has damaged splines and is unusable for a rebuild.
The picture below shows a 928 automatic drive shaft with damage to the shaft just after the splines. This damage was done when it was removed from the 928. Care should be taken when removing the torque tube from the car to not damage the torque tube or drive shafts.
28mm Drive Shaft Problems
The 28mm drive shafts have a propensity to shear at the necked down areas near the splines at each end. Below are a few pictures showing this problem. This failure happens while driving and is signaled by a loud metallic grinding noise under the car and the car no longer has forward or rearward movement in any gear. The top picture shows the sheared drive shaft through the rear torque tube access hole where one would loosen the rear pinch bolt. The bottom picture shows the end of the sheared drive shaft looking into the end of the torque tube.
Due to the shear failures of 28mm drive shafts, it is strongly advised that owners change their 28mm drive shafts with 25mm drive shafts during a torque tube rebuild. We have new enhanced performance 25mm automatic drive shafts which can be purchased for such a change out.