Engine/Transmission (1998.5 - 2002) NV4500 with broken 5th gear, again!!!

[JAlford]

I have a technical question about the NV4500 that I have been getting various answers from trans shops. My NV4500 is fully cryo treated, but I have broken my 5th gear for the second time, stripping the teeth right off the gear on the mainshaft.
I am wondering what the purpose of the cone shaped belleville washer between the 5th gear nut and the 3pc washer assembly (I have fully splined mainshaft from Standard Transmission)? I cannot see why a conical washer is used for that application, and the washer was heavily worn to the extent that the gear was allowed to move 0.01" along the shaft before the break occurred.
Does anyone know, or have a theory on, what the purpose of the conical washer is? Once the gear can move, it seems to wear out on the splines and begins to rock, eventually leading to snapped teeth I assume.
Thanks for any input.
Jeff

 

[SAndreasen]

The washer acts as a spring to hold the gear tight . Unless the nut gets loose the washer can't get loose

 

[JAlford]

Unless the nut gets loose the washer can't get loose

The nut hasn't backed off at all either time the gear has gotten loose. The gear wears a groove into the washer, and I have measured the wear groove against a new washer and also check with a feeler gauge the amount of looseness, and they measure exactly the same, within 0.001". The nut isn't apparently loosening, still staked in the exact spot.

The washer acts as a spring to hold the gear tight .

From what I can tell, the washer isn't a "spring steel" washer, it is stamped steel and not hard at all. Much softer than the gear or the nut. That is what is bothering me about the washer, it wears faster due to the conical shape reducing the surface contact.

Jeff

 

[JAlford]

Let me add some additional info. Yes, belleville washers are spring washers, and typically are used to apply high spring loading forces. What in the retaining of the 5th gear needs a spring load? Is it due to thermal expansion? Is the fact that a spring washer is used against a 3-pc shear retainer washer causing additional wear to occur against the washer? Are the washers that are currently being supplied not meeting the hardness requirement? Are temps causing deterioration of the K value?
I am considering stacking 2 belleville washers to increase the spring capacity, as in parallel the values are additive. But I would really like to understand why it was chosen for use in this application.
Jeff

 

[SAndreasen]

I've never used the washer before with the two halves and a ring retainer I just the halves with loctite on the side that rides on the shaft then loctitie on the inner surface of the ring stick it together let loctite the nut and tighten it down .

 

[NIsaacs]

it wears faster due to the conical shape reducing the surface contact.

Jeff

It might be the nut is not torqued down enough, that it is still conical and not mashed flat. The book calls for 280 ft. lbs, I use 400 ft lbs.

Nick

 

[fox]

If you want 5th gear to survive, it must be driven right. Do not use 5th with rpm below 1800. Do not lug it in 5th.
Owners who understand why, drive them 400,000 miles. I know a guy who says I'm wrong but he is on his 4th fix.

Reason is, the engine pulses as it turns these are called oscillations and the flywheel does not absorb all of it.