Cummins Diesel Forum banner

5th gear nut (not) fix

4K views 16 replies 6 participants last post by  thecheese429 
#1 ·
My truck makes a funny noise in 5th gear, but not in any other gear. It sounds like a whining gear, but only when load is put on it (wheels pushing engine, or engine pushing the engine) but goes away if I push in the clutch or am not loading the engine. I suspected the 5th gear nut had worked itself loose over the 263K miles on my rig, so I got working.:truck:

I went and pulled out a bunch of stuff to get to the tailshaft housing. Pulled it off, and it all looked fine. The gears looked like they had been used not abused (normal wear lines?) and the nut? Looks good.:thumbsup:

What course of action do I take now? While I have it open, should I at least put a bunch of red threadlocker all over the nut? I think that is all that I can do :confused013:

Maybe a previous owner put on a torque king/other mainshaft? Short of pulling the nut and the gear to have a look underneath (I don't want to undo whatever threadlocker is on there), how can I tell if I have the stock mainshaft or a properly engineered one?

As far as the noise, I suspect that the lube may have been low. The synchros didn't seem very stout, which also seems to support that. Or, the noise is normal. I will know once I fill it to spec + some with my newly purchased castrol CD-50 :D

Overall I am happy because this means that before too long I will be back on the road :drool2: :woohoo:

I'll add pictures as soon as I get them taken
 
See less See more
#2 ·
I'm pretty sure you would know if it were any sort of aftermarket setup. Being your's is a 2wd I would leave it be, since it's so much easier to get to. Drain the oil, and refill with Castrol Syntorq LT® 75w85w. CD-50 is not correct, and will damage your synchronizers. Also don't over or under fill it. Just fill it to spec.
 
#4 ·
After reading more on castrol's website, and many threads about this, I have not really gotten anywhere. I have read that I must use GL-4 lubricant, either mopar 4637579 or castrol syntorq. Castrol doesn't have anything on their website for syntorq. They do have syngear, however.

The product data sheet says that the CD-50 viscosity is 75W-90, with a GL-5 rating. It mentions nothing of synchros.

The general consensus I have gathered is that the sulfur compounds in most gear lubes will eat the brass synchros, and that GL-5 is not backwards compatible with GL-4 applications.

What will happen if I put this GL-5 in my NV4500?
 
#5 ·
Your gear looks factory to me. Only use the Syntorque I mentioned above. Amosil has oil for the NV4500 also. Those are the only two that work. The syncros are different in that transmission than most if not all other transmissions.

Dodge dealers (p/n 4874459) and GM dealers (p/n 12346190)

http://www.amsoil.com/storefront/mtg.aspx
 
#6 ·
Well, GL-5 returned and GL-4 ordered. Now I have to wait.

In the meantime, back to my original question. What would you recommend in this situation? I feel like I might as well brake-clean the shaft behind the nut and put some threadlocker on it.

As far as that, I suppose reassembly is the next action.
 
#11 ·
I don't think I would touch a thing on it. If the gear seems tight and all I wouldn't remove the nut to put thread locker on. Are you talking about putting thread locker on the exposed threads? If so that won't work. Need an anaerobic environment for it to cure. I think your situation falls into the its not broke, don't fix it category. If you were 4x4 then I would recommend updating the shaft and all that because it's such a pain to get into. Don't take my advice on the gear as gospel tho. I only preach about the oil :hehe:
 
#12 ·
you got a welder? tack the nut onto the shaft with a welder in 4 spots then it cant come off... Kinda ruins the shaft if you go to rebuild it tho...
 
#14 ·
Then you run the risk of ruining the temper of the nut and shaft and one or other will eventually break. If the nut breaks there is a good possibility it would fall into the gears and lock the whole thing up. As was said, if it ain't broke don't fix it. From what you posted about the noise I doubt new oil will fix it anyway. When you get it rebuilt get a fully splined shaft and gear.
 
#13 ·
I wasn't about to remove the nut and undo the threadlocker (that has been working for 260K miles), just put some on the outside.

I do have a welder, but I couldn't really bring myself to go and ruin the shaft like that, even though it is the root of the problem :confused013:

I am happy to say I am in the small category of people who have not had a problem with the NV4500 :D

Now I just have to go to the junkyard to get a new cross member to replace my bent up one.
 
#15 ·
as far as that noise that you heard goes if it was a high pitch squeek like a belt and changed with clutch throw look into throw out bearing.
mine did the same thing so i replaced the throw out bearing and it fixed my problem.
the only way to really fix that 5th gear is like was mentioned before replace the shaft with a full spline.
good luck
 
#17 ·
I have put the tailshaft cover back on, but when I had it off, I noticed what appeared to be a washer about 2mm thick between the nut and the 5th gear. Not sure if this is stock or what, this thread is about the extent of my experience inside of transmissions

The more I think about it the more I think that the noise could be normal. It is not a constant noise, and I don't hear it in any other gear. It shifts around fine, the synchros feel a little weak but that could just be its age. The teeth on the 5th gear(s) look physically smaller than the other gears. Not to mention that the tranny mount could have been transmitting more noise than it should with its bent and almost torn vibration dampener.

I just put some red locktite on the nut when I had it open, then cleaned everything and put some make-a-gasket on the surface, and put it back on. I still need a tranny crossmember and vibration dampener
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top