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mainshaft nut

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Hi, just experienced the fifth gear problem yesterday, i was hauling my trailer, when all of the sudden i hear a noise and vibration from the transmission. After that my fifth gear will not work any more, luckily made back in fourth. Today we drop the transmission to see what was the problem, and i find that the nut on the mainshaft came loose and my fifth gear and mainshaft gear were gone. I've been searching on the internet and found out this is a typical problem for the NV4500 transmission. Just ordered the gears and need to order the nut also. Having a hard time picking a design that works, would appreciate any input or experience on the parts i need to fix my truck. Thanks.

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The only real fix is to fix the mainshaft by replacing it with a fully splined one. It's called the torque king shaft at this website. http://quad4x4.com/NV4500_Transmission_Kits.html The nut just screws back on and pushes the gear back onto the splines, then it will work fine, but it will just come off later down the road. If you have a 4wd you should probably do something now since it's a little hard to get to. You can tighten it back up and use the updated nut but it will usually just spin back off. Mine seems to do it every 50k miles or so. To prevent it you should keep RPM's over 1900 when your in 5th, less than that and the engine power strokes become a hammering effect on the nut, breaking it loose. I simply tighten mine back up and call it good, but I have a 2wd so it's a 20 min job. It is pretty expensive to get that torque king mainshaft, but it fixes the real problem. You can get updated nuts and tighten it real tight and it might hold for a while. I truly believe keeping it over 1900 AND not letting off and stepping on it (working the play of the gear, which also hammers the nut of course), keeps it from happening, but I like running under 1900 so I pay the price of 20 min.. This is my writeup on the basics of it http://mopar.mopar1973man.com/cummins/general/5th-gear/5th-gear.htm You can weld it but that really isn't the best idea..

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    I was actually going to point you to that but last time I looked at it, it was still in the testing phase. Definitely worth looking into, might have to get one myself. From what I can tell from the pics, you just tighten the nut up and once the nut is tightened up, you just put their locknut thing on the spline that happens to line the keyways up. Simple enough. Much more viable than getting that million dollar torque king shaft. Of course now I see it's only for 4wd trucks since I have a speedometer gear there :banghead: Back to the drawing board.If you're really tuned into you're truck, you can feel the nut loosening up. The play in 5th between when you are giving it power and aren't will tell you everything. When you tighten the nut back up, 5th is very tight, as it gets loose you will get more and more play in the gear until it finally pops off. It's not a ton of play or anything but it's definitely noticable, it's really obvious when you fix 5th gear and then drive it again and feel how tight it is. Once you have that comparison of a tightened 5th gear nut feeling and that loose 5th gear nut feeling, it will be very obvious when the nut is coming loose.

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    I was actually going to point you to that but last time I looked at it, it was still in the testing phase. Definitely worth looking into, might have to get one myself. From what I can tell from the pics, you just tighten the nut up and once the nut is tightened up, you just put their locknut thing on the spline that happens to line the keyways up. Simple enough. Much more viable than getting that million dollar torque king shaft. Of course now I see it's only for 4wd trucks since I have a speedometer gear there :banghead: Back to the drawing board. If you're really tuned into you're truck, you can feel the nut loosening up. The play in 5th between when you are giving it power and aren't will tell you everything. When you tighten the nut back up, 5th is very tight, as it gets loose you will get more and more play in the gear until it finally pops off. It's not a ton of play or anything but it's definitely noticable, it's really obvious when you fix 5th gear and then drive it again and feel how tight it is. Once you have that comparison of a tightened 5th gear nut feeling and that loose 5th gear nut feeling, it will be very obvious when the nut is coming loose.

    so far its been $275.00 for mainshaft gear and fifth gear countershaft gear, still need new shaft nut and oil about $100.00, labor will be about $100.00 thats $475.00. I think i will add the extra nut retainer for another $150.
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