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Old 02-21-2017, 10:44 PM   #1
shawn66mcl
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NV4500 vs SM456 vs SM420

I'm sure this has been brought up one way or another, but my question revolves around my transfer case. I have a 67 K20 with a Rockwell T221 and a good condition SM420 along with a spare SM420 transmission that needs new syncros on 2nd gear. My issue is my T-case is pretty much shot due to no parts per say available for a rebuild. I want to swap to an NP205, but I'm not finding much in the way of adapters for an SM420 to an NP205. Ideally this would be the cheapest solution but if I can't find a way to do that, I'm considering an NV4500 so I have overdrive. I know the SM456 is a little cheaper than an NV4500, but I plan on actually doing long trips on the highway and what not and thinking the of might come in handy. I don't need the super low granny gear and for a difference of about $600, I think it might be worth it for the newer trans. So if anybody has any suggestions on an adapter to the SM420, the best place to purchase an NP205 or also the best place to purchase an NV4500 would be greatly appreciated. I'm pretty handy and could rebuild any of them with a manual so I know junkyards, but I'm not opposed to buying a refurbished unit. If there's something else you guys can think of I'm missing or could use would be greatly appreciated.
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Old 02-21-2017, 11:03 PM   #2
dieseldude4bt
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Re: NV4500 vs SM456 vs SM420

If your Rockwell is shot the sm465 and 205 would be the cheapest option but I would look for the NV4500 for the reasons you listed.
I have one in the classifieds but shipping would be cost prohibitive.
Good luck in your search.
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Old 02-21-2017, 11:12 PM   #3
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Re: NV4500 vs SM456 vs SM420

My thought is the 420 and 465 are comparable, and great for their day, and designed to the driveline.
A truck w/ x rating, came with an engine and therefore driveline based on options decided by the buyer, or bought off the lot.

Or rather start w/ the engine. A small six would have a manual trans and high numerical rear gear.

The point is, match the engine, trans, and rear gear.

NV4500 likes a late NP205, or adaptor. Look around. you can get early adaptors but look for a round pattern NP205, as a start.
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Old 02-21-2017, 11:12 PM   #4
mongocanfly
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Re: NV4500 vs SM456 vs SM420

Ditto on the nv..I swapped my sm465 for the nv and have never regretted it..but mines 2wd..the overdrive was well worth it
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Old 02-21-2017, 11:26 PM   #5
franken
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Re: NV4500 vs SM456 vs SM420

A 4:10 rear and NV4500 is pretty good. Maybe too good. But drive it.
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Old 02-21-2017, 11:33 PM   #6
shawn66mcl
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Re: NV4500 vs SM456 vs SM420

I have the stock 4.57/4.56 gears that came in the eaton HO56
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Old 02-21-2017, 11:36 PM   #7
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Re: NV4500 vs SM456 vs SM420

Any idea what trans?
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Old 02-22-2017, 08:53 AM   #8
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Re: NV4500 vs SM456 vs SM420

I'd go with the 4500. Early years had a steep 1st gear similar to the 420/465, then later it wasn't as steep. Prolly find an older one cheaper and easier, the newer ones are compatible with Cummins swaps and bring more money. One truck I built had a 465, with a 454, 4.10s and 35s was a good compromise, still could haul and still haul ass lol....
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Old 02-23-2017, 03:38 AM   #9
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Re: NV4500 vs SM456 vs SM420

Id be looking at the later 4500. I think that the break point for the more modern one is either 94 or 95. Get the one with the square shift tower as opposed to the rounder one. IIRC, in addition to the more streetable 1st gear, they also have a syncro reverse (which is nice) and revised / updated shift forks that aren't prone to dragging as much as the earlier versions.

I had thought of coupling a 4500 to the 205 with one of the adapters out there. After much reading and searching, I found a '93 2wd 4500 for 700$ and a Dodge divorced 205 for under 200. Yes its a divorced set up and not as compact as a married unit but works flawlessly and was much cheaper than the married unit. Arguably it was way less $$.

One other thing to consider is the dreaded 5th gear nut failure. I could be wrong but 2wd transmissions are way less prone to this problem being that the 5th gear nut is on the outside of the trans and holds the rear yoke on (visible) unlike the married version which cannot be seen unless disassembled for inspection.

To be fair though, I usually hear about 5th gear problems when behind a Cummins for understandable reasons.

They are easy to build with a manual and a few special tools (really good snap ring pliers) a press and a grinder.

If you do buy used, be ABSOLUTELY sure that the correct Syntorque or approve equal was used. If you get one with regular gear oil in it, you will be missing some snycros. This sucks to find out on your first test run.
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Old 02-25-2017, 12:19 AM   #10
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Re: NV4500 vs SM456 vs SM420

When I replaced the blown up NV4500 in my '95 it was the same one as in my '92...and I think the last year for that design.
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Old 02-25-2017, 02:02 AM   #11
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Re: NV4500 vs SM456 vs SM420

Quote:
Originally Posted by special-K View Post
When I replaced the blown up NV4500 in my '95 it was the same one as in my '92...and I think the last year for that design.
I knew it was somewhere in those years.

BTW Tim, how'd yours blow up? I know they're not bulletproof but I am curious. Was it blown up like 5th gear problem or blown up like ventilated case blown up?

I never got the feeling that the 4500 was as durable or abusable (if thats a real word) as a 465 but I love that 5th gear too much to go back to a 1:1 final. I don't baby it by any means but I am a little more careful with it than with the 465.
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NV4500 Reverse Build Thread http://67-72chevytrucks.com/vboard/s...=reverse+build

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Old 02-25-2017, 09:17 AM   #12
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Re: NV4500 vs SM456 vs SM420

lots of 4500 melt down the input bearing cause the factory level is a tad low.

lots of guys say over fill the case 1 pint over stock fill point . do this by dumping it down the shifter tower hole.
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Old 02-25-2017, 08:53 PM   #13
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Re: NV4500 vs SM456 vs SM420

The original trans in the '92 lost 5th a little over 100k miles. A lot of blued parts when I went in so bought new GM crate. Then I got a '95 and that one broke a shaft or something a about the same mileage. I never tore into it, but it went all at once with nasty noises and no more go. Put a crate in that one,too. Totalled that truck about 15k later. One front corner of the case got broken out, but I saved it. Fast forward to 250k+ and the '92 trans started making chatter and it was a chunk of 3rd broke out. I used the '95 innards in the '92 case...plus a few new parts.
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Old 02-26-2017, 12:28 AM   #14
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Re: NV4500 vs SM456 vs SM420

Take a look at the Novac web site. They may have the adapter you need plus they are w wealth of information. They were great when I was rebuilding my SM420 and NP205.

https://www.novak-adapt.com/knowledg...ssions/manual/
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Old 02-26-2017, 10:27 AM   #15
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Re: NV4500 vs SM456 vs SM420

1995 and down has the the lower 6.34 first and wide shift gate, '96 and up has the 5.61 and slightly narrower shift gate. 1993-94 has non sychronized first gear and reverse, the rest are fully sychro'd.
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Old 02-26-2017, 11:25 PM   #16
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Re: NV4500 vs SM456 vs SM420

Good info. Thanks
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Old 03-28-2017, 06:42 PM   #17
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Re: NV4500 vs SM456 vs SM420

I prefer the nv4500 over the sm465 surprisingly not for the OD but for the synchros. We used to own an 88 gmt400 465 truck that had to pull about 6k through SOFT sand unfortunately 2nd was less than useless at any point under about 20mph in this scenario. So I had to constantly either bog the truck in 2nd or ride the rpms in 1st. Now granted this scenario is very limited and most people won't have the problem but once we got a 99 gmt400 nv4500 truck shifting from 2nd to 1st was the same as any other gear. I will say the 465 feels more robust per say I guess it just has a more mechanical hard to shift to feeling vs the 4500s more fluid feeling but I can't say one or the other is better as our towing is strictly limited to 7k or less and we never go over 45mph and we're always in 4lo and neither truck is driven nicely to say the least.
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