NP246 Compatibility

[21Actual]

My lady's truck, an 04 GMC K1500, 5.3, 4L60E has begun making what sounds like chain slap in the transfer case. Shes got 291,000 kms on her, quite frankly I'm surprised the trans and T-case have lasted this long. The sound is 100% coming from the T-case. Same sound in 2wd, 4hi and 4lo. Possible bearing worn, but sounds an awful lot like a loose chain. However, it does not exhibit the chain skipping ratchet sound that I have heard many of these trucks make when under load in 4x4. Oil is kinda dark, but nothing out of the ordinary. I've seen much much worse.

I know these 246's have a few common weak points/issues, one being the front case getting worn as a result of the oil pump wearing a hole. I'm aware of the fix for this, and will be doing it to either the existing t-case if I rebuild it, or to the used t-case that I may purchase. Have yet to decide on a used one or a rebuild. Need to crack open the one in the truck and see what the damage is, then decide if Im going to order parts, or go with a junk yard unit.

To the question, what is the difference between the 99-02 and the 03-07 NP246 t-cases?

Only thing I'm aware of is that the earlier model always spins the front shaft, even in 2wd, and the late model does not.

I am being told they are not interchangeable.

Anyone have some insight on this?

 

[21Actual]

I figured out why they are not compatible. Its all with the encoder motor and shift fork mechanism. 99-02 has two electrical plugs, and 03-07 has a single electrical plug. They are also splined different.

It is possible to tear into it and swap out the shift forks to make an early unit compatible with the late encoder motor but might as well overhaul the unit if your going to do that.

I found a used one locally with 111,000 km's on it for $400. And I have ordered the updated oil pump housing to install before putting it in the truck.

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[Jrgunn5150]

I figured it had to be something like that, since the case and chain don't show a year break. Glad you got it sorted.

 

[clubber]

Just in case you don't already know how bad the stretched chain thing is, my 243 did the chain slop thing for a week before the T-case broke nearly in half. Don't use the truck much before you change it out.