NV4500 Welding Of The 5th Gear Retaining Nut* - Diesel Bombers

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Old 01-15-2008, 08:39 AM
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Default NV4500 Welding Of The 5th Gear Retaining Nut*

Well yesterday I had the pleasure to work on a friends 97 Cummins with the famous NV4500 5th gear issues

It has been a problem for years of the retention nut on the mainshaft to back off allowing the 5th gear to slide out of place

My friends 97 had this happen once so he purchased a new 5th gear and modified retention nut with 3 set screws in place to secure after the jam nut was fully torqued ..................needless to say I aint real impressed with how well it worked as it only lasted 2 years till he had no the gear again

So after consulting with my friend he opted not to but the new upgraded mainshaft , 5th gear and retention nut but reather went for a new gear and nut with set screws and had me tack weld the jam nut after torquing it down inplace

First thing we did was to pull the truck into my nice heated garage since it was -3 outside....had a couple cups of coffee then dove in with both feet

we removed both drivelines, then drained the oil from the t-case and transmission.....pulled the t-case out and set it out of the way then removed the tailhousing from the NV4500 to expose a retention nut backed off all the way and a real sloppy 5th gear ........removed that and installed the new gear and nut then with a special socket to fit the mainshaft and a 2 foot breaker bar and a 3 jaw socket to fit the nut we torqued the new nut down to as much as we could ...............then run the 3 setscrews into place ..................cleaned up the area real good to be be free of oil residue and built a cardboard backer plate to shield the welding splatter........I tacked the nut to the mainshaft in 3 places .....the nut aint backin off and the heat exposure was mimiumal since it was with a MIG wire feed and very quick............I quenched the final product with oil and we buttoned up the truck so it could hit the road.

Do I recommend this proceedure................NO

however I spose it will buy my friend some time so he can build funds to purchase a new mainsaft and do this right.................in other words this time when the 5th geasr fails it only has one fix...........I simply hope that when it does fail it doesnt damage anything else in there in the process

here are some pics of the final result as well as a pic of the new gear, washer and nut


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