advice on regearing vs tranny swap vs overdrive

[space wrangler]

i'm working to restore a 77 4x4 with an HT 383, SM465, and an NP205.

i plan on running 33" tires. ..however, the 3/4 ton axles i have are geared at 4.10. after consulting some gear calculators, it's obvious that 4.10 is going to be way to low for 33" tires. ...so my choices are to regear to 3.73, which still may be to low, or to 3.42. this is likely to be the cheapest option. ..but it may not be as the axles i have now already have lockers in them. i'd have to purchase the new gear sets as well as new lockers for both axles if i go the regear route.

another option would be to swap in an NV4500, but i'm concerned about how much modification would be needed due to the extra length and how to adapt it to the NP205. i've also read that they aren't as reliable as the SM465. ..on the other hand, the NV4500's snycro'd 1st gear really makes driving much more pleasurable than than the SM465.

i also have read a little about overdrives such as the ranger gear splitter, but again, i'm not sure what other modifications would be needed to correct for the extra 7.5" of length it adds. from what i can tell, it would require relocating the xfer case xmember towards the rear and obviously shortening the rear drive shaft. how big of an issue is this? does the rear shortened drive shaft cause vibrations due to the increased operating angles? is that something i'd even need to worry about with only 4" of lift?

sorry for the lengthy post. but i'm at a point where i need to decide what direction i'm going ..and i can't make a decision.


mods, if this needs to be in the 4x4 folder, please move it over for me. ..i didn't think about this being 4x4 specific until after i posted it.

[Your41Plague12]

Personally, I'd leave it as is. 4.10's and 33's is just about perfect. It will have power off the line but not fall on its face on the highway. The 383 should have more than enough balls to keep it moving at higher speeds. That combo of gears and tires should roast them, too!

[donut]

Drive it like it is and see how YOU like it, then decide. I contemplated the same thing with my '73. Time ran out and I kept the 4.10's and stock size tires (31 or 32"). Yes it turns 3000@70mph, but I don't see changing it if I get it back.

[76stepsidechevy]

I have a 350 sm465 and np205 with 3.73s and 33s and its ok. I don't know how anyone ever drove it on the highway before though, it had 30s on it when I got it. Right now I can do 65 at 2500 rpm 75 at 3000 which isn't bad I guess. Mileage sucks tho since I do mostly highway driving. I don't even use low gear in the trans unless im inching along in traffic or trying to pull something out with the truck. even first is kind of a pain to get into. you really need to be completely stopped, even rolling a 2mph its fighting me trying to get into first. More gears would make my truck so much nicer to drive.

Ive thought a lot about the nv4500 swap but at the moment its a lot of coin to throw at an old truck and being my dd I can't have it down for more than a long weekend or so. If I didn't enjoy having a manual trans as much I'd stuff an 700r4 in it and call it good but wheres the fun in that.

Theres no real easy answer I guess. Its all how much work you want to do and how much money you want to spend. If I had 4.10s I probably also consider going to a 35 inch tire.

[Your41Plague12]

I agree also, a 4" lift and 35's would help things tremendously as well as looking awesome.

[yousesteers]

I have been contemplating this my 1984 Chevy 1ton with the Cummins and NV4500 has 4:56 gears w/265/75/16 I want another overdrive thinking about a gear vendors unit but not completely sure yet

[SCOTI]

A typical later model GM drivetrain ratio w/an OD trans would be a 29" tall tire, a 3.42 ratio axle, & a .70 OD gear: 3.42 / 29 = .1179. The goal should be to keep it as close to that calculated result as possible. So your considered options yield:

3.42 / 33 = .1036 (less torque multiplication than the 'typical' engineered GM set-up)
3.73 / 33 = .1130 (slightly less)
4.10 / 33 = .1242 (slightly more)

If anything, when swapping to larger OD tires, opt for a better torque multiplication to get the truck rolling easier (better gearing = motor "working" less).

[324matt]

Originally Posted by yousesteers

I have been contemplating this my 1984 Chevy 1ton with the Cummins and NV4500 has 4:56 gears w/265/75/16 I want another overdrive thinking about a gear vendors unit but not completely sure yet

Cant beat a gearvendor. Buy one.
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[BigBlocksRule]

Originally Posted by 324matt

Cant beat a gearvendor. Buy one.
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You'll have to drive the wheels off of one to pay for 'em, they're way expensive.

[yousesteers]

Found a couple that are not going to be that more expensive than 2 set of gears and carriers.

[space wrangler]

thanks guys! ..i think i'll stick with the 4.10's for now. it's the cheapest option, and they're already installed.


as for running 35" tires. ...is that possible with only 4" of lift? seems like the tires would get into the sheet metal pretty good when they're stuffed. ....and if it's possible, is the trick to run an 8" wide wheel as opposed to a 10" wide wheel? ..if so, i'm definitely going to go with 35" tires. i'm just trying to keep it as street friendly as possible yet still fully functional.

[Your41Plague12]

Originally Posted by space wrangler

thanks guys! ..i think i'll stick with the 4.10's for now. it's the cheapest option, and they're already installed.


as for running 35" tires. ...is that possible with only 4" of lift? seems like the tires would get into the sheet metal pretty good when they're stuffed. ....and if it's possible, is the trick to run an 8" wide wheel as opposed to a 10" wide wheel? ..if so, i'm definitely going to go with 35" tires. i'm just trying to keep it as street friendly as possible yet still fully functional.

Unless you're seriously offroading you'll be fine. That combination is just fine for street/mild offroad use, plenty of people do it. You hit the nail on the head, run an 8" wide wheel. You'll be really happy with the way it looks, it's the way these trucks should have sat from the factory; like one of the 70's Ford "High Boys."

[space wrangler]

Originally Posted by Your41Plague12

Unless you're seriously offroading you'll be fine. That combination is just fine for street/mild offroad use, plenty of people do it. You hit the nail on the head, run an 8" wide wheel. You'll be really happy with the way it looks, it's the way these trucks should have sat from the factory; like one of the 70's Ford "High Boys."

[76stepsidechevy]

backspacing has some to do with it as well, I have 33s on 15x10s with a 4" lift now and theres plenty of room for 35s. Ive ran 15x8 with 33s as well, the wider wheel stretches the tire a little more so there a little shorter.

[SCOTI]

33's is the tallest I'd go using 8" wheels. 10" wheels for the 35's get my vote.

[Your41Plague12]

I would personally go with an 8" wide wheel and 4" backspacing, you won't have any problems at all with that setup.

[324matt]

Originally Posted by BigBlocksRule

You'll have to drive the wheels off of one to pay for 'em, they're way expensive.

You dont have to drive the wheels off of one to pay for it. Mine cost $2650 new. $500 install with shortened shaft. I have a 454 4x4 with 4.10 gearing. So Ive spent $3200(ish), if, gas jumps from $3.15 to $3.75 and I achieve 1mpg better fuel economy from the gearvendor, it wont take long to break even. Besides, there are a TON of guys on here who would gladly pay half of my initial inveatment for the G.V. If I ever decide to sell the truck. So then Im only trying to recover $1700 in fuel savings. If you can afford one, buy it and sell it when your done. Save money, have a toy, and make someone elese happy in the end
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[yousesteers]

Originally Posted by 324matt

You dont have to drive the wheels off of one to pay for it. Mine cost $2650 new. $500 install with shortened shaft. I have a 454 4x4 with 4.10 gearing. So Ive spent $3200(ish), if, gas jumps from $3.15 to $3.75 and I achieve 1mpg better fuel economy from the gearvendor, it wont take long to break even. Besides, there are a TON of guys on here who would gladly pay half of my initial inveatment for the G.V. If I ever decide to sell the truck. So then Im only trying to recover $1700 in fuel savings. If you can afford one, buy it and sell it when your done. Save money, have a toy, and make someone elese happy in the end
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At this point I would probably give $1700 for it my gears and carriers are gonna cost close to that and this would give me double the gears how hard is the gear vendors to install besides the shortened shaft

[324matt]

Originally Posted by yousesteers

At this point I would probably give $1700 for it my gears and carriers are gonna cost close to that and this would give me double the gears how hard is the gear vendors to install besides the shortened shaft

How odd, i was just reading your build thread and you commented my quote. Anyways, its a pretty easy install. Ive seen your build thread, your very mechanically inclined so it would be a piece of cake for you. I had mine installed by a local shop, Im fortunate enough to be able to afford to have someone elese work on my stuff. Good luck!
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[yousesteers]

Originally Posted by 324matt

How odd, i was just reading your build thread and you commented my quote. Anyways, its a pretty easy install. Ive seen your build thread, your very mechanically inclined so it would be a piece of cake for you. I had mine installed by a local shop, Im fortunate enough to be able to afford to have someone elese work on my stuff. Good luck!
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I work on mine for therapy I kinda enjoy it gets my mind off of work and lifes other things