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Old December 29th, 2010, 05:18 AM   #1
JoshG
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Default 4.10 to 3.42 for better fuel mileage?

I have a 1998 3/4 diesel 4x4 suburban and the 6.5 has a #8 cylinder wall crack, so I am rebuilding a 6.2 that I got for cheap (don't have a lot of money and needed something economical).

The 6.5TD ran at 2500 RPM's at 72mph and I think the truck would have a tic increase in fuel mileage if I had 3.42 gears coupled with the 6.2 engine.

What do you guys think? Is it possible/practical? Would the truck more likely be running around 1900rpm's with the different gears? Did they even make a 3.42 front differential that will bolt in place of my 4.10 or will the best I'll be able to do is the 3.73?
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Old December 29th, 2010, 06:04 PM   #2
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if you really wanted to swap gears you would be alright with 3.73's if you don't tow anything.
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Old December 29th, 2010, 06:25 PM   #3
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You would be better with 3.55

3.42 is little too much you would need cruise 90 mph to get rpm 2500

3.55 is perfect.
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Old December 29th, 2010, 09:12 PM   #4
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At 70mph I'd like to be around 1900 rpm. Milwaukee, is there an option to get 3.55 into my 1998 3/4 4x4 Chevy Suburban?

Oh, and I don't really ever tow anything of any significance. If I did I would just leave it in 3rd gear.
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Old December 29th, 2010, 09:38 PM   #5
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Quote:
Originally Posted by JoshG View Post
At 70mph I'd like to be around 1900 rpm. Milwaukee, is there an option to get 3.55 into my 1998 3/4 4x4 Chevy Suburban?

Oh, and I don't really ever tow anything of any significance. If I did I would just leave it in 3rd gear.
gm never made a 3.55 gear. 3.42 or 3.73 are the closest things. with a 3.42 you would be at 1900 but your gonna spend almost a grand on 2 axles with a 3.42 gear. they did offer them but it was sorta rare on a 3/4 ton 4x4 to get that low of a gear. unfortunatly gm never offered a 3.42 gear in the suburbans. only the pickups. i'm not 100% sure they interchange.
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Old December 30th, 2010, 01:05 PM   #6
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Kodiak, I have found some 3.42 front ends between $200-400 and I could change the ring and pinion on the rear end to get the right gear (with a little help from some friends)...but the front ends all say for 6 lug trucks.

I'm assuming that means they are not compatable with my 8 lug...anyone know for sure?

I had never heard of 3.55...I believe Dodge has that gear ratio.
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Old January 14th, 2011, 06:18 PM   #7
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My blazer 1986 came with 3.42, 700r4, N/A 6.2, 31X10.50X15. It sucked ass pulling a 2 place trailer and 2 sleds at max I could hit was 50MPH with 850 degrees exhaust temp ( max for the 6.2 engine is 1100-1200 degrees ) now I have 3.73 and 31X10.50X15 and hit 65 MPH and about 650 degrees with same trailer and sleds!

Next phaze will be adding a banks turbo and 2 stage Methanol injection

Chevy used with there diesel engine ( n/a 6.2, T 6.2, n/a 6.5, T 6.5
3:08, 3:42 fuel milage and 3:73, 4:10 for towing
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