996 Nightmare -Thrust Bearing Failure
#31
Rennlist Member
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I'm not sure I'm understanding how disengaging the clutch is creating a thrust load on the crankshaft??? Wouldn't engaging the clutch release the load on the flywheel/crank?
#32
Former Vendor
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The pressure plate in the clutch system is over 3,000 pounds of force. When the clutch pedal is depressed the release bearing contacts the pressure plate to release the clutch. To do this, it must fight the load of the pressure plate.
So, since the pressure plate is attached to the flywheel, and the flywheel is attached to the crankshaft, this force is placed longitudinally on the crankshaft. Its the job of the crankshaft thrust shims to carry this load.
But at start up there's little lubrication on these shims, so the forward facing shim is solely responsible for carrying these forces made by the pressure plate. If the clutch is depressed to start the car, then this makes for the worst possible scenario for the crankshaft thrust shims, as they start dry, and with all that load.
This makes them wear thin, and fall out of the crankshaft carrier... Then the crankshaft starts banging around, and when you pull off the oil sump to help diagnose the issue you are faced with whats left of the shim laying on the sump plate.
I documented this as mode of failure #17.
So, since the pressure plate is attached to the flywheel, and the flywheel is attached to the crankshaft, this force is placed longitudinally on the crankshaft. Its the job of the crankshaft thrust shims to carry this load.
But at start up there's little lubrication on these shims, so the forward facing shim is solely responsible for carrying these forces made by the pressure plate. If the clutch is depressed to start the car, then this makes for the worst possible scenario for the crankshaft thrust shims, as they start dry, and with all that load.
This makes them wear thin, and fall out of the crankshaft carrier... Then the crankshaft starts banging around, and when you pull off the oil sump to help diagnose the issue you are faced with whats left of the shim laying on the sump plate.
I documented this as mode of failure #17.
Last edited by Flat6 Innovations; 07-01-2017 at 04:30 PM.
#33
Burning Brakes
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The pressure plate in the clutch system is over 3,000 pounds of force. When the clutch pedal is depressed the release bearing contacts the pressure plate to release the clutch. To do this, it must fight the load of the pressure plate.
So, since the pressure plate is attached to the flywheel, and the flywheel is attached to the crankshaft, this force is placed longitudinally on the crankshaft. Its the job of the crankshaft thrust shims to carry this load.
But at start up there's little lubrication on these shims, so the forward facing shim is solely responsible for carrying these forces made by the pressure plate. If the clutch is depressed to start the car, then this makes for the worst possible scenario for the crankshaft thrust shims, as they start dry, and with all that load.
This makes them wear thin, and fall out of the crankshaft carrier... Then the crankshaft starts banging around, and when you pull off the oil sump to help diagnose the issue you are faced with whats left of the shim laying on the sump plate.
I documented this as mode of failure #8.
So, since the pressure plate is attached to the flywheel, and the flywheel is attached to the crankshaft, this force is placed longitudinally on the crankshaft. Its the job of the crankshaft thrust shims to carry this load.
But at start up there's little lubrication on these shims, so the forward facing shim is solely responsible for carrying these forces made by the pressure plate. If the clutch is depressed to start the car, then this makes for the worst possible scenario for the crankshaft thrust shims, as they start dry, and with all that load.
This makes them wear thin, and fall out of the crankshaft carrier... Then the crankshaft starts banging around, and when you pull off the oil sump to help diagnose the issue you are faced with whats left of the shim laying on the sump plate.
I documented this as mode of failure #8.
#34
Rennlist Member
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The pressure plate in the clutch system is over 3,000 pounds of force. When the clutch pedal is depressed the release bearing contacts the pressure plate to release the clutch. To do this, it must fight the load of the pressure plate.
So, since the pressure plate is attached to the flywheel, and the flywheel is attached to the crankshaft, this force is placed longitudinally on the crankshaft. Its the job of the crankshaft thrust shims to carry this load.
But at start up there's little lubrication on these shims, so the forward facing shim is solely responsible for carrying these forces made by the pressure plate. If the clutch is depressed to start the car, then this makes for the worst possible scenario for the crankshaft thrust shims, as they start dry, and with all that load.
This makes them wear thin, and fall out of the crankshaft carrier... Then the crankshaft starts banging around, and when you pull off the oil sump to help diagnose the issue you are faced with whats left of the shim laying on the sump plate.
I documented this as mode of failure #8.
So, since the pressure plate is attached to the flywheel, and the flywheel is attached to the crankshaft, this force is placed longitudinally on the crankshaft. Its the job of the crankshaft thrust shims to carry this load.
But at start up there's little lubrication on these shims, so the forward facing shim is solely responsible for carrying these forces made by the pressure plate. If the clutch is depressed to start the car, then this makes for the worst possible scenario for the crankshaft thrust shims, as they start dry, and with all that load.
This makes them wear thin, and fall out of the crankshaft carrier... Then the crankshaft starts banging around, and when you pull off the oil sump to help diagnose the issue you are faced with whats left of the shim laying on the sump plate.
I documented this as mode of failure #8.
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#35
Former Vendor
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These thrust shims (2) are the VERY FIRST part thats installed when reassembling an M96 engine. Once the crank carrier is assembled, it holds the shims captive, and they can't even be seen.
This one is a 100% teardown to remedy.
That clutch switch is a really stupid addition to these cars, mechanically speaking. Any car I won has any switch like this bypassed, and I start the engine with my foot off the clutch, transmission in neutral.
Of course, I am the type that rips every safety switch off every piece of equipment, or car that I own. If I hurt myself, its my own damn fault, but I'll be damed if some safety switch is going to fail and leave me on the side of the road, or in the middle of a field!
#37
Former Vendor
#42
Rennlist Member
#43
Rennlist Member
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I would think that the cruise will not work with the switch "jumpered" - under normal operation the cruise drops if the clutch is depressed... perhaps a way around this is to wire a switch (one of the open dash positions?) that will jump the switch without pushing the clutch pedal. Once the car has started, you can turn the pedal switch back "on" which will allow the cruise control to operate as it normally would - i.e. Drop off if/when clutch is depressed.
#44
Drifting
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I would think that the cruise will not work with the switch "jumpered" - under normal operation the cruise drops if the clutch is depressed... perhaps a way around this is to wire a switch (one of the open dash positions?) that will jump the switch without pushing the clutch pedal. Once the car has started, you can turn the pedal switch back "on" which will allow the cruise control to operate as it normally would - i.e. Drop off if/when clutch is depressed.
#45
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I would think that the cruise will not work with the switch "jumpered" - under normal operation the cruise drops if the clutch is depressed... perhaps a way around this is to wire a switch (one of the open dash positions?) that will jump the switch without pushing the clutch pedal. Once the car has started, you can turn the pedal switch back "on" which will allow the cruise control to operate as it normally would - i.e. Drop off if/when clutch is depressed.