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Modified Tech Tech forums for Modified M715 series vehicles

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  #41  
Old April 12th, 2011, 06:28 AM
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It all comes down to what you want the truck to do.

Taller than 38" tires, hi power engine swapped in and planning to climb walls. Then, the stock front axle is probably not stout enough to last. Especially if a front locker is installed.

Stock engine, hi powered ground pounder, 38" tall tires or smaller, no front locker and no hard core beating planned. The stock axles will probably last longer than the sheet metal.

The 5.87 gears in the stock axles are what lead most people to swap. Plus the closed knuckle, king pin, drum brakes and $200+ lock out hubs. By the time you change to a more street friendly ratio, put on lock out hubs and think about disc brakes. A set of CUCV D60/14b axles with all the goodies could be purchased with all the good stuff and money left over.

It all comes down to what you want to do. CUCV axles have tripled in price over the last 8 years or so. Now it is a dead even swap money wise.

I left mine stock, put on lock out hubs in front, a locker in the rear and my 396 Big Block has a NV4500 bolted behind it to turn the XZL tires. But, I am limited to 54 mph because of the NP200 tcase on long trips. The axles physically aren't the problem, just the gear ratio inside. A NP205 is my answer to the speed thing and the axles will be left alone.
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  #42  
Old June 6th, 2011, 05:37 AM
77amc 77amc is offline
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Sorry guys, but Im ignorant about all these numbers and such describing axles.

I'm not into going straight up with the Jeep, Just haul with it and maybe pull a 5th wheel at some point later.
I don't know just by looking at a particular transfer case if its' a np200/np2xx OR 14 bolt from a 70.
SO, if I go to a 'yard'/pull it, What year ___ do I look at?
Some describe a 'dually' rear.. Does that mean you adapted your Jeep for a dually axle or did you mod it to have just one tire on each side?

Does anyone know or have pics of axles/t-cases that come with 4.10 gearing?
Here in the Memphis area, there are literally TONS of HD trucks around in the yards but don't want to be swapping a 5-700lb rear more than once

E
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  #43  
Old June 6th, 2011, 06:33 AM
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E,
The higher the number, the more mechanical advantage the engine has and the more pulling power the truck has. That is how the stock 120 hp engine is able to pull 1-1/4 tons of cargo off road. Gears, not power make it happen.

The lower the number for the gear ratio, the more highway friendly a vehicle is. However, it also becomes more pulling limited. The M715 was designed to haul 2500 pounds off road up to around 30 mph. Then to be able to run down the road at convoy speed of maybe 45 mph. It does that perfectly.

People wanting to run faster, have more powerfull engines installed or that don't care about the pulling power. Often want to get rid of the stock 5.87:1 axle gear ratio.

Gears can be bought all the way down to 4.56:1 gears. However, here is where it gets complicated. The Chevy M1008, M1028, M1031 CUCV 1-1/4 ton CUCV trucks all came with 4.56 gears in them. They also had a locker already installed on the rear, normal 8 lug bolt patterns for the rims, open knuckle front axles, front lock outs, disc brakes on the front and rear disc kits available for not much money. That is the Dana 60 open knuckle front/14 bolt corporate rear mentioned above. 1977 to 1991 depending on the model 1 ton GM trucks had these axles. However, lockers on the rear only happened on the M trucks.

There are a lot of semi floating 14 bolt rear axles out there compared to the CUCV full floating rear.

I would suggest you rear as much of the modified section post about axles and truck builds as you can to get a better understanding of all this because I really didn't scratch the surface. Just tried to explain the basics.
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  #44  
Old June 6th, 2011, 07:14 PM
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Barrman, I'm 'all up' with the gearing ratios, it's just terms like CUCV, M1008 yadda yadda that get me all cornfused.. I have no idear whatcher tawkin 'bout!!

I would LOVE pics of these rears (NO pun intended) I've pulled up some seaches but would like a link to a list with pics/casting #'s and Maybe even U-joint sizes.

There are a couple of LARGE pull a parts here in the Memphis area, and with all of the trucking here also, there's tons of vehicles that can be 'sourced' for parts. That is if The diff cover is still on them..
SO, I need to print out some pics of transfer cases and rear ends, memorizing them before I crawl under dozens of trucks.

I'd just hate to buy something that I DON'T need..

There were others that said to ask questions.. SO there..

Sorry, I'm in a goofy mood.
Errol
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  #45  
Old June 8th, 2011, 06:59 AM
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Google images would be your best bet. Do a Google image search for the CUCV and such and you will see what Barrman is talking about.

Questions are indeed welcomed and encouraged, but an effort at self-help will go a LONG way here on the Zone.

As for rear axles you can pick up at the yard, look for a tab on one of the differential cover bolts. That's usually where the gear ratio is indicated. If the cover's off of a wrecking yard axle, I'm probably going to pass on it anyway, but you could count the teeth to determine the ratio.
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  #46  
Old September 12th, 2011, 09:21 AM
77amc 77amc is offline
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OK, the way some talk of these axles is like they know some black magic telling them what gears are in them.
I'd doubt that 'yards' will let you pull off every cover off draining all the lube out that you'd be interested in.

Tried to look for the little tabs stating gear ratios on the cover bolts that are either rusted or broken off, and some CODE on the info plate that needs to deciphering..

Are those the only two ways of getting the ratio?
E
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  #47  
Old September 12th, 2011, 09:39 AM
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The ratio is just a way to represent how many times the drive shaft turns for every time a tire goes around once. Grab the drive shaft yoke (Pinion) and turn it around and around until the tire/axle shaft/brake drum on one side goes around 1 time.

Did you almost make it 4 times around? 3.73 gears.

A hair more than 4 times around? 4.10 or 4.11 gears.

Did it do about 4-1/2 times around? 4.56 gears.

Almost 6 times around? 5.87 gears.

3-1/2 half times around? 3.42 or 3.55 gears.

Just a hair more than 3 times around? 3.08 gears.

There are only so many number of teeth that can be on each gear inside the differential. The list I just made I think are all that could be combined for a 14 bolt.
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  #48  
Old September 12th, 2011, 05:40 PM
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Now that I have it stripped down to a rolling frame, I'll use some tape and roll her around.

I've gotten messed up before by trying to do that with both tires off the ground and someone mentioned to have BOTH tires on the ground.. (Didn't make sense to me at that time either) but I couldn't argue because for some reason, it was off like almost 3/4 turn..

At least I'll only have to do one end.

I still think that there should be an axle 'sticky' showing them WITH CLEAR pictures!

Errol
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  #49  
Old September 13th, 2011, 06:08 AM
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Here is another write up that says the same thing in a little bit different way:

http://www.jedi.com/obiwan/jeep/misc/gearratio.html
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  #50  
Old January 19th, 2012, 12:53 PM
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so im thinkin about an axle swap and have a quick question. For those of you that have 2.5 ton rockwells, what sort of highway speed are you able to maintain? From the research Ive done, there are no re-gear kits available for the 2.5ton rockwell that would allow you to change from the stock 6.17(i think) down to 4.56 or something more suited for highway speeds. only reason i ask is they are beefy axles and i found a pair for cheap. since i eventually want to run 46" tires it might be a good upgrade for me. any thoughts?
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