Drive Train

Drive Shaft Breakage

I've recently come across PCNA service bulletin no.9206 which covers the issue of broken central tube shafts (drive-shafts) on M.Y. 1989-1991vehicles equipped with automatic transmissions. Apparently, these failures are caused due to faulty ignition monitoring systems via defective exhaust gas temperature sensors & ignition coil wiring. PCNA states this condition as, "Oscillations in the central tube system that occur when the ignition monitoring system has switched (flywheel effect) can lead to breakage of the central tube shaft". These failures seem to occur at engine speeds of approximately 1000 rpm.

A local 928 owner here in Montreal had told me that the drive-shaft on his '91 automatic had failed at a red light several years ago and the dealer was supposedly stunned when they found the shaft sheared into two pieces. At the time, I was sure that he had probably abused the car but I guess that's not the case. The funny thing is that this bulletin was published in 1992. Figure that one out......

A modified drive-shaft was later introduced bearing part no.960 421 012 07

Has anyone on the list had this experience?

Andy Evangelidis
'91 928S4 horizon blue/cobalt
member 928oc



Yessirree, mine snapped but I was on the track. All the other failures I've heard of occurred at contstant or low RPM while just driving around town. In my case I was at redline in third ('88 S4 A/T) and just as I shifted into "D" it let go. I don't recall the shift completing, meaning I don't remember actually getting fourth gear and than having the shaft go, it felt like I went from third to neutral.

I've compared pictures with others that have sheared their shafts, and Jim Bailey introduced me to a pile of sheared S4 A/T shafts up close and personal at 928 Int'l. They all break the same, looking just like a piece of peeled string cheese.

My shark was running very strong, and I had a hard time believing the drive shaft failure could be caused by any type of ignition or brain failure. Sure enough, my LH brain toasted a few months later. Maybe something intermittent was going on, I sure couldn't feel it though. I'm not convinced that this was the cause, but have no other explanation.

Mark A. was nice enough to line me up with an older constant diameter driveshaft, which seems to be the best fix available. I don't know of any stock S4's that have snapped one of the older shafts, but then again I don't see them as often as some.

-Adam Birnbaum
'88 S4 A/T