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Discussion Starter #1
I been thinking about adding an OverDrive trans to my 62 GMC i been told GM has 2 5spd's a Direct Drive 5th gear unit and an Over Drive 5th gear unit . . .

Dose the OD 5spd also still have a Granny ?

was its ratios in compared to the SM420 4spd ?

Mike
 

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Discussion Starter #2
Ok I found that GM made 2 OD 5 speeds ...
They recommendations from GM is to use the first generation NV4500 for replacing the SM420.

SM420 1st gear 7.05:1 4th 1:1.

Gen 1 NV4500
1st gear 6.43:1 5th .73:1.

Gen 2
NV4500 1st gear 5.03:1 5th .74:1.

Then they went on to say that the GEN 1 made a much better replacement trans for the SM420 as the transmission had the closest matched first gear and the slightly steeper over drive !

Mike
 

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Pardue the Traveler
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have you considered a splitter or overdrive for the SM420
 

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Discussion Starter #4 (Edited)
I would prefer to just swap out the transmission and be done with it. . .

How can i tell which is a Gen 1 or Gen 2 NV4500 ?
Is there any known issues with them ?

It'll be installed behind a 379 cubic inch V-6 Gas engine making [email protected] n [email protected]

when pull the cab off the truck to drop on a replacement cab i was going to have the engine rebuilt and the block decked n heads milled for just a touch more compression, heads ported n polished over sized valves. then replace the 175-225cfm ? the tiny carter 2bbl and replacing it with the 500cfm Holley 2bbl.

Do you think i'll really gain much for power ?

if so will it be within safe numbers for the Gen1 NV4500 ?

Mike
 

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Discussion Starter #5
So about the Generation 1 and Generation 2 GM OD 5spd manual transmission how dose go about IDing such a unit ?

Mike
 

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Pardue the Traveler
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I use to know but I have forgotten which is which.
 

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Discussion Starter #7
Well that sucks...

If you think of it email me.

Mike
 

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Pardue the Traveler
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Will do, if I remember. I learned the difference when I was thinking of replacing a Sm420 with a NV4500 in an 64 gm pick up that I was thinking of doing as a project long ago. :thinking
 

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as mentioned , gm used two versions of the nv4500 5spd. 92 through 94, maybee 95, had the low first gear like the gm 420 and 465 tranny's. memory serves me correct, 95 was the last year of the low hole gear. this being said, the latter tranny, does a good job on launching heavy loads also. i have these trannys in gm 6.5 powered trucks. one is a 94 the other a 96. there is a difference in the bolt pattern in the newer style tranny[ same pattern as dodge used]. again i believe this started in 95, may have been 96 though. lot's of info and sites on the 4500, do a google search! bewarned, the earlier verson is hard to find, lot of mudders and rock crawlers look for this tranny for their conversion jobs and such.
 

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Discussion Starter #10
I'm looking for it to put in my 62 GMC behind my big block 379M V-6 I would rather keep my low granny gear as I to crawl around the the soft ground n muddy terrains, tho I don't do any rock crawling but have had my fair share of downed trees to climb over.
I also pull a great deal of weight with this truck.

So I would prefer the lower geared unit.

I'm basically looking to gain and over drive with out adding a secondary trans.

Mike
 

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got ya! i'am thinking of doing this same thing to my k2500, with a 6.2 diesel and 4.10 gears, it really needs the 465 manual ditched for 4500. albeit i believe the 420 and 465 were tougher tranny's though..
 

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Discussion Starter #12 (Edited)
Ya but I'm tired of running [email protected] I would rather be running 65 at 2600-2800rpm or 2500-2700rpm...

My 379M V6 makes [email protected] n [email protected]

Blow up rpm is 3700...

So I'd like run slightly faster at a slightly lower rpm...

If I could run [email protected] I'd be happy...

Tho it loves rolling 3000rpm so if it don't like the slower rev then ill just run faster at the same old 3000rpm...

Its a brute of a V 6 4.561 bore 3.86 stroke GM actually classifies them as a big block V6.

I think it'll pull the 27% OD its got 5.13 gears and 8-19.5s

Like I said it turns 175hp n 388tq with the little Carter 2 barrel 175-225 cfm ? Is tiny.

Anywho it'll be going up to the big holley 500cfm 2 barrel when I do he trans swap...

Just to make sure it'll pull the over drive...

Mike
 

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yes sir, those gmc v6's were hella'va stout engine's. reliable as a rock too. my 62 gmc is a 2500 with the 420 tranny and 305 v6, 4.10's in the rear. cant tell how many times i have put the inline 6 boy's in their place with this old truck. same story all the time, some boy thinking their inline engine is where the trq's at.
 

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Discussion Starter #14
Yup my lil V6 LOL out pulled its fair share of I6's n s few V8's even !

Mike.
 
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