New To Duramax Diesel.

dirtyLB702

dirtyLB702

New member
May 13, 2011
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florida
New to diesel I have worked on them before and friend and family have had them for years so I finally bought me a lb7 duramax and I live it got a couple questions though. I noticed while going on the high way its reving in the 2k + range at like 65,70mph its a 2500 and it has the 3500 rear end.It also is a canadian truck but some how got down here to fl. Now should it be reving like that? It gets horrible gas mileage bc of it.
 
ecc_33

ecc_33

Junior Member
Aug 10, 2006
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Amanda, Ohio
seems about right. The truck should have 3.73 gears. iirc when i had 3.73's mine would be at about 2200 rpms at about 70mph
 
SmokeShow

SmokeShow

Well-known member
Nov 30, 2006
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Lawrenceburg, KY
What size tires are on it?

Mine with 32-33" tires is right at 2000rpm at 72mph. Shorter tires will be more RPM for a given speed. So, stock tires (29-30" tall I believe) will put you at about 2200rpm at 72mph or there abouts.

If, for some reason, the reaend that was swapped in was from cab&chassis 3500, there's a chance it could have lower gears (4.10s) & your RPM would be considerably higher at interstate speeds than the numbers posted above.
 
dirtyLB702

dirtyLB702

New member
May 13, 2011
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florida
Thank-you for the welcome guys. And smoke show believe it or not it was an option when u bought the truck but they only did it for a certain time so their kind rare and yea it does have a 3500 rear end in it same with the drive shaft and what not. It has 33" tires but with a tape measure they measure 35"
 
SmokeShow

SmokeShow

Well-known member
Nov 30, 2006
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Lawrenceburg, KY
So does it have 4.10 or normal 3.73 gears? That'll make a huge diff. I'm guessing it's got 4.10 if your RPM are up there on the interstate with 33" (and especially with 35") tires. And yes, the highs RPM is going to kill your fuel mileage.
 
SmokeShow

SmokeShow

Well-known member
Nov 30, 2006
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Lawrenceburg, KY
Except cab & chassis... I coulda sworn you could 4.10 in the c&c trucks, no?


He's either got low gears or no OD & I'd guess he'd have more issues with his trans if it no longer had OD as there are components/packs associated with OD that are related to other gears as well, right?
 
blk smoke lb7

blk smoke lb7

<-----Lots of green $
Nov 8, 2010
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belvidere,ill
No if you got a 3500 there is an option for the 4:10 im betting the guy before him that changed the rearend did the front diff as well and now he is rolling on 4:10s

3:73 is the only option for the 2500 iirc
 
LWATSON

LWATSON

future trans limpers
Jul 30, 2008
2,587
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Scotland Neck NC
Going out on a limb here but I really "think" there has never been an option for ratio on a Dmax powered pickup. The gearing in the trans was specifically chosen to work with the 3.73. There is a ratio option for the gas powered trucks 2500 and 3500.
 
dirtyLB702

dirtyLB702

New member
May 13, 2011
38
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florida
I was saying the 3500 parts were an option not the gear ratio. Im not sure what gear it has in it I was just guessing by the rpms and what Yall said but now it sounds like I do have the 373 gears in it.
Also another question what will make my turbo louder cause u cannot hear that thing outside the truck at all lol I hate the sound of it.
 
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