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Discussion Starter #1
ok i got a c4 that im about to take to rebuild, i want to take my c6 off and replace with the c4(ive heard its the thing to do). so the question is, am i going to have to get a different drive shaft bar(i think thats what its called)??? i dont know if the c4 and the c6 are the same length. the car is a 72 mustang with a 351c.
 

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C-4 is shorter, so it takes a longer drive shaft. Also it takes a different crossmember. The C-6 crossmember is a nice piece to pay for the swap. Converters are different, PA sells a spline adapter. All in all the swap is worth it.
 

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question. Are people swapping out the C6 for C4's because of size? I mean size for size the C6 would be the stronger tranny although you can rebuild a C4 to take quite a bit of torque and HP but if you build up a C6 to the same specs it would be a stronger tranny, yes? I understand that there are a lot more C4's out there than C6's so maybe that's why people use the C4 over hunting down a C6. I guess space is also a consideration (header clearance).
 

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Also a c4 takes 35 hp less to drive than a c6 does. That means 35 more hp to the rear-wheels without touching the motor.
 

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When referring to drive shaft bar, are you referring to the drive shaft itself or the yoke? Like previously stated, the driveshaft needs to be longer. The yoke also needs changed. The C-6 has a bigger splined output shaft.
 

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Also ,make sure to get the correct C4 flexplate.The c6 flexplate sits the convertor deeper into the trans and can damage the front pump..
 

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Discussion Starter #8
thanks for the info guys. so to do the swap i understand i will need the c4 flexplate, i already have the converter for the c4. is there anything else besides this and the longer drive shaft?
 

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The yoke is the splined section on the front of the driveshaft that slips into the transmission.The c6 has a 31 spline yoke and the c4 is smaller and has 28 splines.
 
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