Dear all at the 928 forum. I have a 1978 928 with a manual transmission and during a drive today I heard a bang followed by a scraping noise. I was shifting from second to third when this happened and no more gears. Got towed home had to press down the clutch pedal all the the way while getting towed. When not pressed down there was a scraping noise, and when pressed down it went away. So... Could a blown throwout bearing cause this, or could it be the spline on the shaft worn out? (Or the clamp tube?) Thank you in advance..!


A good drive while it lasted, a fine day in may, windows rolled down aaaand clunk...<br/>

 

Welcome to Rennlist.

This could be a torque tube broken shaft.



Lift the car, remove the cover and you'll know if this is the case.

Good luck.

 

Thank you! And thank you for your reply. I will do just that and report back.

 

that photo that Bertrand Daoust put up how on earth did that happen?

 

not unusual at all....the shaft metal fatigues and breaks. Porsche stated that running on 4 cylinders will do this. The excessive twisting of widely spaced firing events.

 

As I understand shaft failure is quite a rarity on manual transmission models - all too common on later automatic models.

My theory for the auto models is that the shaft slips in the front clamp and creates compressive stress in the shaft that induces the fatigue and then "pop". No idea what can happen to cause such in the manual variants - too much time on the clutch pedal possibly??? Whatever the cause it is likely something that will have been manifesting itself for quite some time.

 

Check your rear clamp on the input shaft to the gearbox. Not unheard of to have the gearbox hollow input shaft crack, and eventually break, as a consequence of a loose rear clamp/bolt and major spline wear.

 

Sorry I am am of no help in your diagnosis, but a Silver OB with what appears to be Cup II's requires more Photographs of the car. Love it!

 

Thank you for all your input! Expecting the worst, I have felt some shudder from the car under acceleration sometimes. I am for the time being without a garage so I am at the mercy of the weather. No work done yet. Meanwhile I'll post some random pictures of my car.

 

This-^

Based upon OP's description, the drive shaft is snapped. And likely at the rear.

There's a rubber-plugged inspection hole at both ends of the tube through which the drive shaft ends can be observed.

 

Again, very grateful for all your input! Thank you! A couple of more pictures, hanging out in the rain:

 

Beautiful car!

 

Thanks! I will post some pictures of the interior soon also... (It is entirely original and has some, ahem, patina going on...)

 

Both ends are fine, inspected with a microcamera also. Suspect clamp, or clutch or release bearing or possibly all. Will drop manifold and cover when I have the time. Seems like opinion differs whether you can drive with a busted release bearing or not. Any experiences?

 

Car raised safely, and with the bottom cover of the bellhousing removed, car in gear and running, parking brake set (or better: assistant has foot on the brake), look look through those inspection holes to see what's turning and what isn't. You'll hear the grinding noise too, which will steer you to the failure. From front to rear:

-- There's a splined stub shaft in the front between the front of the driveshaft and the rear of the crankshaft, has the clutch plates on it.

-- There are splined clutch plates.

-- There's a clamp where the stub shaft fits into the driveshaft in the torque tube.

-- There's a clamp at the rear where the driveshaft connects to the input shaft on the gearbox.

-- The input shaft on the gearbox...

-- The stuff inside the gearbox.