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General Discussions about the 300M

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 #378633  by remi
 April 15th, 2019, 4:55 am
Hi guys,

I've been having a thought lately about my Special. As a recap, previous owner was racing another car on the highway when connecting rod #4 broke. The next explosion cycle pushed the 4th piston down its cylinder and the crankshaft smashed it in the block, bending the crankshaft, as it would not turn over without removing the nearest main caps.
So I guess the engine suddenly stopped turning while the transmission was still going pretty fast, probably in 2nd or 3rd gear. The guy was able to coast and parked on the side of the road.

Thing is... the last time I had a friend over we went for a ride (I'm not driving the Special much these days, after hitting someone's side mirror :( ) and I pushed her a bit. Between like 4500 and 5000 rpm (or 5000-5500 can't remember for sure) I could hear and feel through my feet a huge vibration. It would go away over 5500 rpm and is absent bellow 4500. Subframe mounts are probably shot on this car, it's shaking on each pot hole so this vibration might not be related to the transmission (I guess any damage would make a more permanent noise).

The transaxle is still working ;) but I wonder what the damages could be. I haven't run an oil checkup yet but I will.
Have you guys ever heard of such sudden stop before?
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 #378634  by FIREM
 April 15th, 2019, 6:23 am
The sudden engine stop would not likely have an impact on the transaxle itself. The Torque Converter may be another story.
Converter turbine driven by the engine would have stopped immediately, and pump drive stopped, but the transaxle would have tried to drive the converter until it unlocked. So for a split second there may have been some reverse forces within the converter. Doubt this would have done any damage, kind of like when an engine stalls. All trans functions cease as the oil pump is no longer driven.
M's have a tendency to have a slight "harshness" in the RPM range but not a huge vibration. Mounts and driveline angles would what I would look at.
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 #378807  by remi
 April 26th, 2019, 7:18 am
Thank you Bob for your answer.
FIREM wrote: April 15th, 2019, 6:23 am Mounts and driveline angles would what I would look at.
How can I check the driveline angles?
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 #378859  by FIREM
 April 29th, 2019, 10:23 am
I can not find any specifications or checks for driveline angles. We do know from experience that those that have installed lowering springs without using mount spacers have induced vibrations.
About the only thing I can think of is to measure ride height to confirm springs/suspension has not sagged. Inspect engine and trans mounts for signs of damage, and sub frame mounts.