3.07 diffs & np435?

u2slow

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Curious of anyone has/had a 4x4 with 3.07 diffs, and a grunty 4spd? Was it truly pathetic? Or tolerable? What gas engine?

Kind of trying to decide how to best use my Dana 61/71 axle pair. (Dodge)
 

Black dawg

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Had a friend that drove a chevy pickup , 3.73 with 35s and a 465 trans. Was a stock 350. Always seemed to work ok. Could still take off in second fine.
 

u2slow

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Hmmmm.... 35" is probably 315/75R16 and actually 34"? Lookin at an rpm chart, I'd have to get down to a 28" tire to match that.

400ci and 31's is what i had in mind.
 

XOLATEM

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I remember fixing up a chevy truck for a customer one time about...oh...twelve years ago...had a bad clutch and a broken front retainer on the 3sp w/OD...(New Process unit adapted to a chevy bell from the factory)....the front retainer-to my surprise- was unobtainium...

I sent it off to a shop...I think in Oklahoma...and sent a drawing with the specs on what I needed...and...God Bless Them...they machined up a new sleeve and welded it on and machined it perfect...

The real point of this story is that the clutch was wiped because the truck had 3.07's front and rear and was a slug and the guy used it for towing...

I fixed up his clutch, transmission, and advised him to get me to put 3.73's in it front and rear...and when it was done I MADE SURE the gears were properly broke in before I gave the truck back to the guy...

Worked gosh-darn perfect..!!! That was a job that I was sorry I did not buy the truck from the guy...it worked so good...

Can't remember if it was gas or diesel...all I remember was the amount of grunt on takeoff...it was GREAT...for what it was...

I used it to get 1200 dollars worth of rebar on my car trailer...once the gears were broke in good...had to tie the stuff to a tree and give 'er a good yerk to get the stuff unloaded...did not have a front end loader back in those days...

Anyway...it seems...in my humble opinion...for a lot of street applications...that 3.73's work out pretty good...if you have overdrive....

Just my .02...
 

u2slow

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I remember fixing up a chevy truck for a customer one time about...oh...twelve years ago...had a bad clutch and a broken front retainer on the 3sp w/OD...(New Process unit adapted to a chevy bell from the factory)
Thats the NP440 aka a833. More like a car trans. Only 3.09 1st gear.


The NP435 has a 6.68 1st... and i don't mind using 1st on these HD 4spds. Oh well, no rush for this; just spitballin' and pondering ;burnout
 

XOLATEM

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Thanks for the input @u2slow...it was good to see the spec sheet on that trans...I liked that unit so much that I bought a core unit from someplace near you and rebuilt it, found a shifter from a 'yard...and I had planned on putting it in an '86 chevy with a 305 and a 3.73...one day...

That one is on the 'way back burner...right now I am in a torrid love affair involving a 6.9...

Yeah, I can see your point on not needing the steeper gears with your granny-gear unit...that is a lot of potential grunt with that first gear...
 

WECSOG

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I've owned and driven quite a few trucks with granny low 4 speeds. With a gas engine, I would not go numerically lower than 3.73. Preferably 4.10.
I'm pretty sure it would be a miserable driving experience, with the huge jump between 1st and 2nd. Non-synchromesh on first wouldn't be awesome either.
 

u2slow

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I'm pretty sure it would be a miserable driving experience, with the huge jump between 1st and 2nd. Non-synchromesh on first wouldn't be awesome either.
That part I'm confident will be fine. I had a suburban I geared to 3.21 with the Sm465. (6.2 diesel though). 1st gear was most often used to start. Syncro doesnt matter because its pointless to downshift into 1st.
 

Cant Write

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Not apples to apples, but my dad and I have owned a 2:56 geared C10 mild 355/TH350 (low stall) for almost 30 years. 29” tires. (235/75-15)

NEVER have i once wished for OD and steeper gears. We have grossed 12-13k hauling lathe and plaster to the dump.

we have dollied a car (‘88 park avenue) 6 hrs, could not tell it was back there. Got the same 12 mpg as when it’s empty.

Taken it on 9 hr one way road trips to CO. Will run 80 all day long. Due to wind resistance it loves 72-73.

It’s got plenty of stop light to stop light pep. And when I hit a hard hill loaded I can do 60mph in 1st gear easily. (4500 rpm)

I love the combo for light duty use!!! And I’m happy to have a simple 3-spd. It’s dads daily driver as his 4.6 grand marquis is dumping oil in cylinder 8.

I think your first Spit-ball hit the bullseye!! 3.07’s, granny-4, and skinny 235/85-16’s for the win. I’d love that combo in my burb with a 6.2.
 

Cant Write

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Heck to take it further cause now you got me drinkin’ and dreamin’

I’d love to convert our c10 to manual steering and brakes just for the sake of simplicity. And drop a 6.2 diesel in it to putt around in.

But that prolly sounds dumb to most. And it currently just works so well.

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Front edge of dads C10. And my burb I stupidly sold!!

On the other side of the coin, that burb was TBI-350 TH-400 and 4.10’s. Took it 13 hrs to ID and I’d set the cruise at 75 mph (3400 rpm) and just let it sing. Would still get 12 mpg.
 
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u2slow

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Not apples to apples, but my dad and I have owned a 2:56 geared C10 mild 355/TH350 (low stall) for almost 30 years. 29” tires. (235/75-15)
...
I think your first Spit-ball hit the bullseye!! 3.07’s, granny-4, and skinny 235/85-16’s for the win. I’d love that combo in my burb with a 6.2.
Impressed to hear you managed 2.56 in a truck with an auto - and not be useless! I'd have been concerned with how much heat/slip happens when loaded; something you avoid with the manual.

I think my puzzler is where the rpm/torque ends up at common road speeds. A diesel has such good torque at the bottom it almost doesnt matter. Maybe I'm overthinking it... the gas engine has a wider rpm range.

Probably do 265 tires for the extra 400# weight capacity. It is a clubcab longbed I'm targetting; np435 is married to a np203.

That 6.2 Burb I re-geared/re-trans'ed.... went from 12mpg to 17! It also effectively became a C30 with a front suspension/brake swap, and a 3.21 FF axle wearing the 13x3.5" brakes. 33" rear tires just because.

Edit: I had an older C10 ('66 longbed stepside) with all the manual stuff. Loved it. It was a 292/sm420. Almost diesel-like torque curve there.
 

Black dawg

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Remembered a couple more I had experience with. 91 2wd half ton suburban with a 273 geared 12 bolt somebody put in it. Was probably the nicest highway cruiser I have ever had. 700r4 with low first gear made it work just fine. Tires were 235 75 15. Had no issues holding overdrive and would get 20+ at 70mph.

Other was a 70s chevy 4x4 3.07 or 3.08 gears, 4spd and a 396. Had 33s on it. It did seem somewhat underpowered , but got around just fine and got pretty decent mpg.
 

Cant Write

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Was just watching this, love station wagons, but noticed the build sheet at 6:56.

400 2v V-8, C6, and 2.47 rear gear!! I assume 27” tires.

I think yours with 31’s, and the granny 4 would be a great all around pickup. When you starting the project?
 

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