Xnke Posted September 7, 2009 Share Posted September 7, 2009 Ok, so i installed a FS5W71C transmission into my car the other day, and used a '71 driveshaft, in my '72 model car. I am worried about the length of the spline engagement, I think i may need a longer driveshaft. The original driveshaft for my car measures 22.5" long from the center of the U-joint to center of the U-joint. Since the C box is 2" longer, I figured I would need a 20.5" long driveshaft. Since the '71 cars have the diff mounted 2" forward, the '71 shaft should be the correct length, when used in a '72 car. It does fit into the transmission, once the driveshaft dust collar is removed, and it slides back to bolt to the differential flange with no problems, the splines in the transmission remain engaged and the diff pilot fits fine. BUT, I'm worried about the length of the splines that are engaged-when installing the shaft, I can slide it 2.125" into the transmission! to be clear, that means that with the driveshaft all the way forward into the back of the transmission, there is two and one-eighth inches between the driveshaft rear flange, and the differential flange. WOW, that looks like a lot. Is this too much? is it normal? How can I find out, if the answer is "maybe?"? Quote Link to comment Share on other sites More sharing options...
Xnke Posted September 7, 2009 Author Share Posted September 7, 2009 Ok, Riddle Me this: I have ONE stock F4W71B transmission, with original 22.5" driveshaft, Original R180, original mounting points. All fits, driveshaft has 3/4" front-back motion to enable getting it in and out. I have ONE 240SX FS5W71C transmission, with modified mounting points (mount moves 2" back), 20.5" driveshaft, Original R180, BUT the shaft fits with over 2" of front-back play. NOT RIGHT. So, on a hunch, I pulled the original 22.5" long shaft out of the parts box, knocked the collar off the front, and bolted it in place. Perfect fit, 3/4" front-back motion to get it in place and bolted up. But the transmission still measures two full inches longer than the old one. The differential has not changed position. WHAT DID I DO TO MY CAR?!!! oh man...I swapped the roof and the floors...did I stretch my car two inches?!?! Quote Link to comment Share on other sites More sharing options...
zxtman Posted September 8, 2009 Share Posted September 8, 2009 the position of the engine block did not change... the position of the differential did not change... sounds to me like both tranny lengths are the same, only difference is that the mount on the 240SX FS5W71C is in a different location: that's why the original driveshaft fits. Quote Link to comment Share on other sites More sharing options...
Xnke Posted September 8, 2009 Author Share Posted September 8, 2009 Except its is a known fact that the C box is two inches longer. Proven by the other swaps done, in fact. Weird. Quote Link to comment Share on other sites More sharing options...
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