Wow it's been awhile! Had quite the busy holiday season, of course right in the middle of it I started hearing a whining sound while driving... A couple hundred miles later it was WAY louder than it should be. So, time to diagnose...
After all the transmission problems, I'm pretty in tune to figuring out sounds. So first was the easy test - is this trans, transfercase, driveline or rear end... Shift the transfercase in neutral and "drive" the trans. There is no other way to describe this other than watching the video.
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So, very obvious that the transfercase has
something wrong with it. Pulled the fill plug to check fluid, yup, plenty. Color though..... oh no.
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Due to the holidays, the cold temps outside, I decided to just buy a transfercase.... That turned into a disaster in itself. My truck is a K3500. And for those who aren't familiar... K3500 trucks use a Borg Warner Transfercase with a PTO provision and fixed front and rear yolks. Sounds straight forward right? Nope.
GM used 3 BW cases in these trucks. BW1370, BW4401, and BW4470. My truck has a BW4401. It's a predecessor of a BW1370 (they actually share a ton of parts, and half of the case even says 1370 on it). They used the BW4470 in Chassis Cab trucks which were rated at 12,000 GVW. There is also a heavier version of the BW4401, for crewcab longbed trucks outfitted with RPO 9D6 (11,000 GVW). Both the BW4401 9D6 and the BW4470 use a 1.5" wide chain and gears as opposed to the 1.25", and the BW4470 has a fixed oil pump housing plate which the others do not have. To make it even more confusing up front there are flange (early) and fixed yolk (late) outputs, and in the rear there are slip yolk outputs for early regular cabs, and fixed yolks for the rest.
Oh, did I mention this transfercase has an electromagnetic front driveline synchronizer that is tied into the front actuator? Yup. And because of this it uses a different 4wd harness than the rest of the NP241 trucks and has a firewall mounted relay to control it.
Basically, this was 2 weeks worth of research, and a couple junkyard trips. The cases are like, $1,200 for a rebuilt one, and run $600 or so for a used one, if you can find one locally. They are just simply not common. I thought I had one at a junkyard locally, ended up spending about 4 hours looking through tons of transfercases only to find an early flange front output style, and they couldn't locate the correct one. Another yard had one, and Devin (
@83GMCK2500) went to look at it for me, but it turned out to be a BW4470 (at this time I didn't fully know the differences between them). The fixed oil pump plate added about 1" to the length, so with those measurements I determined I did have enough slip yolk useable to swap that larger case in my truck, so home it came.
BW4470 VS BW4401
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I haven't gotten into it yet, but here is the case out of the truck, in neutral.... Something got fried in there.
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Oh, and I forgot to mention, as much of a PITA it is to pull the transfercase in this (they are about 2x as heavy as a NP241), it was a bit of a blessing in disguise/potential nightmare. Upon myself inspecting things, I found the nut on 5th gear had backed off on my NV4500 and the gear was only 1/2 engaged... Mind you this only has 6,000 miles on it from brand new.......
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I tapped the gear back on, installed the spacer, the OEM spring washer (which was not installed by the trans shop), and a replacement nut with loctite.
Been working fine since.
Another little upgrade, Devin gave me a front receiver he scored at the junkyard.
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