I say a NV5600 if not then an NV4500.

 

Not to be dickish but...

You sir.... are wrong. The nut is exactly what its title describes (a NUT) the NUT is in no way splined, looks just like a spindle nut, it backs off of its own threads (not splines), mostly from being lugged around in 5th gear to much

 

No harm done my friend, poor choice of words on my part. What I meant by spline was the mainshaft, that is the true culprit. Dont know why I was referring to it as the spline. Sorry for the confusion.

 

Someone needs to make one that the threads are cut the other way. But for now the best thing ive seen is the little piece they sell that fits the splines and the notches on the nut and makes it physically impossible to turn the nut, yet its all easily removable.

 

all you need is an NV4500, South Bend DD clutch, Billet input, and 5 gear nut fix and you will have a very reliable trany

 

I just welded my nut stuck...

If i ever need to disasemmble it i will just cut the weld off...

Probably the best fix since i tried every other 5th gear nut fix there was...

for 500hp, i don't beleive you will need the bigger input shaft... but for reliability reasons i would take it...

the 4500 will take endless abuse, i know it from my own experience...

 

i have done both on the 5th nut, (tacked and splined nut) tacking it is an option but not one i prefer. The splined nut is cheap and a very reliable fix.

 

HAha sorry to dig this post up from the past but I did the modification on the nv 4500 with the new shaft and it is so easy to do just take alot of pictures or set up a video camera as your taking it apart so you know exactly how it goes back together. Just get the new shaft FULLY splined threads are the same on all of them easy two day job if you have all your parts on hand , but what I did that I had great luck with before i did the shaft mod if is use lock tightthat is used for sleeve retainer I believe its 60,000 sheer strength and torque that down till you move the engine with it locked in first gear. Then take a small punch and pull out the set screw in the updated nut and make a really good dent in the shaft where that set screw goes so it will have a groove to grab. THenbuy a quality allen wrench and torgue that set screw till u bend or break that allen wrench i know waste of a tool but you wont regret it if you get 20 thousand more miles till 5th falls off again. Anybody here good at rebuilding g56s?

 

My mechanic received his education on the NV4500 at my Cost. The locking nut for 5th gear is a booger. Mine backed off 3 times before he found out it has to be spot welded onto the shaft.

The other question I saw was about the NV4500 5th gear and NV5600 6th gear. My mechanic initially said they were the same He later found that the NV4500 is 1 to 0.85 and the NV5600 is 1 to 0.73. The 4th and final fix was the welded 5th gear nut and up grading to the 1 to 0.73 5th gear.

When having transmissions rebuilt make sure they inspect and VERIFY the transmission case bearing housing is tight and snug. If they do not and you have upped your horse power/torque you can end up spinning the bearing in the housing. That will eventually be BAD.

 

NV4500 is in mine does everything I want it to