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Curse of the 5th gear nut!

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Well my friends truck with NV4500 has a problem with 5th gear nuts we have fixed it a few times now over a couple years now.

 

1st repair put a fancy new nut with set screws and 3 small welds about 1/4 inch wide. Mig welded nut to shaft.

Lasted maybe a year 

 

2nd repair he put the nut back on and mig welded the hell out of it, all the way around the shaft. A couple months later on a long trip with trailer the shaft broke completely where the weld was.

 

3rd repair we put an after market shaft in it with full splines and threads. A very expensive shaft. It had a new washer and nut with it we also replaced the 5th gear. The nut had 3 set screws with little hardened teeth. 

We put the thread lock on the nut and set screws and torqued with a long cheater pipe. We were advised NOT to weld anything.  I also made a custom spacer on my lathe to go between the nut and transfer case bearing as plan b so if it looses up again at least the gear would still stay on the splines.

 

Well it failed again on a long trip hauling a medium trailer. No 5th gear the nut loosened and the shaft actually walked forward in the tranny so my spacer didn't help. The shaft moved far enough that reverse has a hard time staying engaged. 

 

Should I weld it.  It really needs a keyed shaft with a washer that has an internal tooth on it. Similar to the ones in the rear axle hubs.

 

 

20190416_180143.jpg.d365c8e3a82e26934248a6f19a757ade.jpg

 

Here's the old shaft that broke. That orange stuff is from the gear oscillating on the splines. That movement causes the nut to loosen. The fancy new shaft was supposed to be a forever fix.

 

Any opinions or advice? I'm getting tired of fighting it.

 

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Tractorman

Tractorman

Posted
Posted

I have never owned a vehicle with an NV4500.  But, with what I have learned about the NV4500, if I would have owned one that failed, I would have immediately replaced it with a NV5600.  In my opinion the NV4500 transmission is too light duty for a high torque, low rpm Cummins diesel engine.  There is no fix. 

 

The nut loosens or the shaft breaks because the nut loses its clamping force,  It loses its clamping force because it is under-designed for the clamp load.  Locktite / set screws  / Loctited set screws do NOT maintain clamping force.  Welding the nut will cause a properly torqued nut to immediately reduce its clamping force.   For all of these mentioned conditions, when the clamping force is lost the nut will always come loose or the shaft will break.  Every time.

 

I am sorry you are having to go through this.

 

- John

 

 

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Mopar1973Man

Mopar1973Man

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Posted (edited)

Strange 472k miles I've never had a 5th gear nut issue. Now what I had problems with....

 

First off the factory gear lube 75w-85 synthetic is too thin especially when heated to above 220°F. It was causing wear of the gear hard face and cause the gear teeth to break. I've broke 5th gear (smaller one on the mainshaft). I've broke the input gear.  Then had issues with syncros being I got two sets of defective brass syncros. This is why I'm using 50 SAE Transmission fluid which is the same stuff used in Eaton Fuller 10 speed transmission. 

 

Food for thought the 75w-85 is equal to 10w-30 engine oil for viscosity. 

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Edited by Mopar1973Man
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Posted (edited)

So I found out there are different versions of the aftermarket shafts. I didn't get the one with the thrust washer groove that is supposed to fix it with the assumption that the nut will loosen. The downside of that shaft is the machined groove can weaken the shaft and the gear rocking will eventually fail. But this seems to be the preferred shaft. The torque king shaft seems the best designed one.

 

Maybe @Mopar1973Man is on to something. The thicker lube might help cushion / dampen the diesel engine harmonics. 

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Mopar1973Man

Mopar1973Man

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2 hours ago, Great work! said:

Maybe @Mopar1973Man is on to something. The thicker lube might help cushion / dampen the diesel engine harmonics. 

 

Matter of fact @Doubletroubletransmission just blew up his tranmission. Broke the teeth off the input shaft and the countershaft below. Bearings are wiped out too. I was looking at some of the photos and saw where the hard facing on the gear teeth was worn down and grooved. Thicker lube is a bonus 75W-85 is only 10w-30 engine oil. The 50 SAE transmission fluid I use is actually 90-weight gear lube. It's a synthetic GL-4. I know the 2 buckets I've got now both Valvoline and the Mobil 50 no longer show GL-4 rating. I'm still using 50 weight and plan on swapping the ATF+4 out of Thor (2006) and changing to 50 SAE as well. ATF+4 is even thinner than any of the fluids listed.

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kbf98520

kbf98520

Posted
Posted

I just bought this unmolested 01 4x4 ,5spd NV 4500. I was about ready to open it up , verify torque and tig weld a 1/4” at 3 o’clock and 9 o’clock. Maybe I shouldn’t bother?

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kbf98520

kbf98520

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I know the proper fix is rebuild with upgraded shaft, but I thought I’d be alright to weld it (gently) lol, get some more miles out of it , then when it ultimately failed pull it and do it right.
I should just pull it now and do it? At this time it hasn’t been touched. No previous failure

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Doubletrouble

Doubletrouble

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 If you really don't want to pull it at this time you could look into one of the 5th gear fixes out there. They usually come with a new 5th gear, a different design nut/keeper. There are a few designs out there. This could be done in the truck. You'll have to pull the T-case of course. Then remover the tail housing, 5th gear is right there.

 I would not recommend welding it, that will create more issues later when you do dig into it to do it right 

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kbf98520

kbf98520

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5 minutes ago, Doubletrouble said:

 If you really don't want to pull it at this time you could look into one of the 5th gear fixes out there. They usually come with a new 5th gear, a different design nut/keeper. There are a few designs out there. This could be done in the truck. You'll have to pull the T-case of course. Then remover the tail housing, 5th gear is right there.

 I would not recommend welding it, that will create more issues later when you do dig into it to do it right 

I’ve been kicking this around for a few months and from what I see the after market replacement nut packages don’t really hold up any better than original equipment. This is why i thought id weld the original nut instead of buying the aftermarket junk. 

I started a new thread on this instead of hijacking this one

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