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Gears & Diesel

zap275

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My rear axle gave way and looking to rebuild. I have a 6.2 diesel with 700 OD Tranny. I have 35 inch tires. I do not want to sacrifice fuel mileage. I have been told 4.10 gears with a detroit locker will work well with 10inch rear. I would appreciate any help and input. I am looking at spending almost 1000.00 dollars for new gears front and back with bearing kits and detroit locker. I do not want to wind my diesel out on the interstate. Thanks /forums/images/graemlins/k5.gif
 

alec78

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Round about way of answering your question...

To figure engine speed:
(MPH x drive ratio x 336) / Tire Diameter = RPM

Example:
4.10 is the axle ratio; 0.69 is OD ratio; your drive ratio is 2.829. Sooo...
(65 x 2.829 x 336) / 35
becomes
61785.36 / 35
So your engine RPM is 1765ish. Room enough to spare a little faster than 65.

Though with 35s you might want to be looking for a 14bff instead of a 10 bolt /forums/images/graemlins/dunno.gif
 

zap275

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Thank you for your input. I have been shopping around and I am able to have driveshaftspecialist.com build a rear end 10 bolt with eaton posi and 3.73 gears complete ready to install for under 1600.00 dollars. I do not do alot of 4 wheeling mostly road traffic. I think the "14" might be too stout of a rear axle for my truck. How is that set up that i'm considering? I also heard detroit lockers are locked whenever put under a load from the engine.
 

k20

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You cant really have too stout of an axle only prob is the FF is 8 lug, but that can be converted. A 14FF w/ 4.10's for 200, and a detroit for either 3 or 4 hundred, still 1k cheaper than a 10bolt, alot stronger too. And it should be pretty much ready to bolt in. And yes the detroit is locked when under power. So if on the gas around a sharp turn you will chirp the inside tire. Let off the gas, it will unlock and it will be pretty much normal.
 

landcrusher

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$1600 for a 10b... no way.
Spend the same cash (or less) and get the 14bFF! /forums/images/graemlins/waytogo.gif
 

6.2Blazer

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[ QUOTE ]
Thank you for your input. I have been shopping around and I am able to have driveshaftspecialist.com build a rear end 10 bolt with eaton posi and 3.73 gears complete ready to install for under 1600.00 dollars. I do not do alot of 4 wheeling mostly road traffic. I think the "14" might be too stout of a rear axle for my truck. How is that set up that i'm considering? I also heard detroit lockers are locked whenever put under a load from the engine.

[/ QUOTE ]

$1600 for a rear 10-bolt /forums/images/graemlins/yikes.gif /forums/images/graemlins/yikes.gif

I'd go to a junkyard and buy a 3.73 factory geared 10-bolt for $100-$200 WAY before I'd even think about spending that much on a rebuilt rear axle.

For the gears, my K5 with a 6.2/700r4 combo came with 3.73 gears and tiny 235/75R15 tires stock. I ran the 3.73 gears with 32's and 33's and it seemed to be okay, I then switched to 4.10's with the 33's and it worked pretty good (couldn't really notice that much of a difference between the 3.73 and 4.10 gears though). I later switched to 35's and it was pushing the 4.10's a little. So basically I would suggest at least 4.10's for 35" tires if you did mostly freeway type driving.
 

SUBFAN

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Dangit, I will sell you my 3.73 geared 12b for $1600, with ANY locker/limited slip you choose....

For $500 more, I will even paint it for you, your choice of colors /forums/images/graemlins/waytogo.gif





/forums/images/graemlins/whistling.gif /forums/images/graemlins/whistling.gif /forums/images/graemlins/whistling.gif /forums/images/graemlins/whistling.gif /forums/images/graemlins/whistling.gif /forums/images/graemlins/whistling.gif /forums/images/graemlins/whistling.gif /forums/images/graemlins/whistling.gif
 

elacruze

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[ QUOTE ]
My rear axle gave way and looking to rebuild. I have a 6.2 diesel with 700 OD Tranny. I have 35 inch tires. I do not want to sacrifice fuel mileage. I have been told 4.10 gears with a detroit locker will work well with 10inch rear. I would appreciate any help and input. I am looking at spending almost 1000.00 dollars for new gears front and back with bearing kits and detroit locker. I do not want to wind my diesel out on the interstate. Thanks /forums/images/graemlins/k5.gif

[/ QUOTE ]

My '85 6.2 with TH400 and 4.10 gears, 235-85 tires gets 16.5 mpg on the highway. With 35's and overdrive, I'd say that 4.10s are the way to go, but definitely not in a 10 bolt. The 700r4 has a much lower first gear, and with the bigger tires and diesel you'll just kill the axle again. Get a 12 bolt at least, or have those $1600 thieves build you a 6 lug 14 bolt.
My $.02
Eric
 
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