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FS5W71B 5 speed question


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OK Gurus , I've read a lot about the long and short shaft FS5W71B being the same other than the extension housing. What about the main shafts?


I have a short shaft B out of my 85 720 regular cab 4x4 that was noisy, I pulled it apart and it had a bad bearing in the counter gear separator plate. I also noted the main shaft nut had backed off or was loose. I pulled it down and there are also some gears that don't look to good on the ID where they roll on the needles.


I have a good 84 2wd B long shaft transmission. I noticed that the main shaft nut is a little loose on this one too but otherwise the transmission looks good inside. Is it typical to see looseness in this nut after several thousand miles?


My question is, Will everything from the 2wd long main shaft slide on to the 4x4 short shaft? I know the 2wd is geared higher but other than length are all of the main shaft dimensions the same? I think I can make the short main shaft live for a while longer and was hoping to swap shafts and just run the 2wd gear clusters etc.


Part numbers are obviously different from one to the other due to ratio differences, but, is that all that is different? 

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There were some changes after '84. Counter main bearing, 1/2 shift rod, synchros. If you change everything it might.


You should find the the mainshaft nut staked in place and it shouldn't be loose.

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  • 2 weeks later...

Thank you for your reply and thank you for sharing your obvious wealth of knowledge where Datsun and Nissan vehicles is concerned with the rest of us.


Before I continue with summary of my project experience so far I have another question. Do you know a trick to get the shifter striker pin out? I need to change the O-rings. I got the nut off easy enough but the pin wont budge and there's not enough room to get a hammer in there. I thought obout putting some heat on it?


I pulled the 2wd long tail down and it was in very good condition. The short tail had a bad counter main support bearing some bad needle bearing surfaces in a couple gears and the corresponding needle bearings were rough too so building that transmission back up was not an option for me. Fortunately the short main shaft cleaned up nicely with some emery cloth. I bought some seals a gasket  along with a new main shaft and counter gear nut. I basically built the 2wd long tail transmission back up on the 4x4 short tail main shaft with few exceptions. The counter gear bearings were the same on both transmissions


I  think that for my needs the higher 1st, 2nd and 3rd gears from the 2wd transmission will serve me better. Of course 4th gear is direct drive and the same in both transmissions. I parted from the 2 wheel drive gear  ratio configuration in 5th gear however. The 4wd short tail 5th gear and counter gear are both press on so it was easy.The 4wd 5th gear is a little less overdriven. I get little opportunity to use 5th gear in the hills and the engine has a tough time pulling 5th gear. The last thing I needed was the steeper over drive that is installed on the 2wd trucks.


Everything went together very nicely no surprises or difficulties other than a couple that were due to my working on an unfamiliar transmission.

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I think it's like a crank cotter pin on an old bicycle pedal, so it wedges in place. You have a reverse check sleeve on the driver's side. Take it out and maybe you can strike it with a brass rod through the hole? 

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I just drilled and tapped a 1/4" NPT port in my housing, so that I could get a strait shot at it with a punch.

When I am done, I just put a 1/4" NPT pug, with sealer on the treads into the hole.


Make sure you leave the nut on it, just flush with the end of the pin's thread, so the threads don't get messed up.

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