new tranny or new gears??

[Facetime]

I have a 4 spd SM465 that I was hoping to replace with the NV4500. The reason for doing this was due to new 3/4 ton axles that were going in that have 4:10 gears. Wanted the OD to help with daily street pounding which is 90% of what this blazer does. The axles and NV4500 were to allow me to tow the boat the 15miles to the lake which I might occasionally do if the blazer were capable. (boat & trailer are 5000lbs dry) That project is creeping into the $1800-$2500 dollar price range depending on how good a transmission I can find.

I called my driveline guy and he said he can put 3:73 gears in the 14bolt GM that I am putting in for around $800. I have a set of 3:73 gears I can swap into the front axle to match.

My question...anyone know if the SM465 can handle that weight? As a daily driver the truck will have 33in BFGs, do you think the 3:73 gears should get me down the road at 60-65 around 2200RPM? Not great but better than the 4:10s with the same transmission. Thank you for your inputs!!
Cheers.

[RED 1970]

What gears are you currently running?
Also, if 90% of the use is pavement why the need for a 14bff?
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[Facetime]

Got a great deal on the axles and am converting to disc brakes front and rear. Front axle has them already, and the 14 bolt matched, just drums obviously. Had planned the transmission swap but hadn't fully recognized the cost involved. Currently running 3:73 and it has been OK just thought a 5 speed would be lots better and the NV4500 is beefy enough to tow the boat.

[kwmech]

Your existing SM465 can more than handle the weight of your truck and trailer.

[RED 1970]

Originally Posted by Facetime

As a daily driver the truck will have 33in BFGs, do you think the 3:73 gears should get me down the road at 60-65 around 2200RPM?

Doing the math on this and assuming that 33's aren't quite 33" tall you should be turning 2,500rpm at 65mph.

Originally Posted by Facetime

Not great but better than the 4:10s with the same transmission. .

With 4.10's you'd be close to 2,750 rpm at 65.

Using the overdrive of .74 you would cruise at 2,050 at 65 with 4.10's. No personal experience but from what i've read the NV4500 is just fine if you don't end up in abusive offroad situations.

If it were me I'd pay the money for the 5spd manual and go with the axles with 4.10's. It might end up costing $500-$800 more but you'll have way more options.

[Facetime]

As always, great insight from members. Thank you for the information. If I can find the right deal on the NV4500 i am definitely leaning that way.

[Mike C]

IMO, the NV4500 is not money well spent. The SM465 is a more durable transmission that you already have. 35" tires are ideal with 4.10 and the 465's 1;1 4th gear. Put you about 2500 rpm or so at 65 MPH. Great speed for a small block carburetor setup.

By the time you have purchased a 4500, adapted it to your NP205 and manufactured 2 new driveshafts and mounting crossmembers, if you are lucky, it will have cost you $3500.

A set of junkyard axles with 3.73 should run you about $800 for the pair, tops. Other than that, put a 4" lift on it and a set of 35's.

[-Greg72]

Every thread I've ever read about a successful NV4500 swap usually ends with the OP commenting that it cost WAY more than they expected once they got all the "little details" sorted out.... that's something to keep in mind if you're serious about it.

IMHO swapping gears from 4.10 to 3.73 (or vice versa) is a real waste of money. The benefit is minimal. The only reason I'd swap is to match a front axle to a rear axle... but I certainly wouldn't swap gears at both ends. There's more to the story than just getting to a mathematically "nice" cruising RPM with your gearing. 3.73s and 4.10s will feel pretty "doggy" most of the time in a heavy truck with big tires.


-G

[IwantaK5]

I had two dump trucks with Inline 6 and sm465's and they had been in daily service for more than 25yrs without a problem, so i venture to guess the sm465 should be fine to tow a boat. I have also been looking at a NV4500 swap and they seen awfully expensive. Specially to mate it to the early gm NP205.

[Facetime]

Thanks again for all of your insight. After much consideration, posts here, and considerable more research I think I will keep my tranny and see how it goes. The cost certainly started to make me wary. Cheers!
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