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I suspect my 07 Silverado 2500HD may have a 4.10 or a 4.56 rear end

Man With A Gun

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Man With A Gun Enthusiast

Man With A Gun

Posted
Posted

Reasons:

1. Both times I've checked the gas mileage, it's 10.3 and 10.9 mpg, in a mix of about 20% 50mph+ and 80% city. Usually with my other V8 trucks and vans I get around 14-15 mpg for this, my usual daily driving pattern.

2. Also, I believe there is supposed to be a tag somewhere on the rear end indicating it's a 3.73 ratio. It's missing on this truck.

3. The truck came with a 2½ by 2½ hitch receiver, which is for really heavy loads (around 16,000+ lbs I think). If the original owner was towing anything in this range, I would think that a rear end change to 4.10 or even 4.56 would have been on his short list of mods.

The RPO codes indicate the truck was built with a 3.73 rear end.

How can I tell for sure? Do I jack up the rear end, and count the number of drive shaft revolutions per wheel revolutions (or do I have that backwards?)

 

 

Badass69 Senior Enthusiast

Badass69

Posted
Posted

New body style i am assuming as the 6 liter engine 2500hd Gmt800s all had 410 gears. Tire size of course too. If you really think its been regeared jack it up and pull the rear cover off and look. Probably needs an oil change anyway.

 

A 6 speed truck with 373s and the oem 245 75 16s turns around 1800 rpm at 65 mph. If its significantly higher than he may have regeared. 410s don't make that much difference on the trucks mileage wise... like not 4 or 5 mpg. 4.56 would make for a really short first gear too lol.

 

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cliobogger Enthusiast

cliobogger

Posted
Posted

You aren't providing much info. We are to assume you are talking about a 6.0L engine simply because of the gas mileage. However, unless I am VERY mistaken, no 07 NBS's had 6 speed transmissions besides the D-Max. Also, they didn't ALL come with 4.10 gears, most came with 3.73s. All in all, that much city driving and (assuming you only have 4 gears plus reverse), 10-11 mpg sounds about right. my 03 6.0L with 265/70-17s gets about 10-11 mpg average with a 4.10 rear end. Easiest way to tell, jack the truck up, chalk the tires, put a chalk line on the tires themselves (to see how many times it goes around), have someone spin the drive shaft one full revolution and watch how many times the tires go around. Or you can take the rear diff cover off (since who knows the last time the rear oil was changed and you can put fresh good stuff in it), take a wax pencil, draw a line on the ring, one on the tire as well, have someone spin the tire, you count the tire rotations per one ring gear rotation. Both are good ways to tell. Also while you're in there on the second method, you can inspect for any uneven wear or damage since the original owner had such a large hitch on it for towing.

 

Edit: at 60 mph with my set up, I am at about 1800 rpm as well.

Badass69 Senior Enthusiast

Badass69

Posted
Posted

You aren't providing much info. We are to assume you are talking about a 6.0L engine simply because of the gas mileage. However, unless I am VERY mistaken, no 07 NBS's had 6 speed transmissions besides the D-Max. Also, they didn't ALL come with 4.10 gears, most came with 3.73s. All in all, that much city driving and (assuming you only have 4 gears plus reverse), 10-11 mpg sounds about right. my 03 6.0L with 265/70-17s gets about 10-11 mpg average with a 4.10 rear end. Easiest way to tell, jack the truck up, chalk the tires, put a chalk line on the tires themselves (to see how many times it goes around), have someone spin the drive shaft one full revolution and watch how many times the tires go around. Or you can take the rear diff cover off (since who knows the last time the rear oil was changed and you can put fresh good stuff in it), take a wax pencil, draw a line on the ring, one on the tire as well, have someone spin the tire, you count the tire rotations per one ring gear rotation. Both are good ways to tell. Also while you're in there on the second method, you can inspect for any uneven wear or damage since the original owner had such a large hitch on it for towing.

 

Edit: at 60 mph with my set up, I am at about 1800 rpm as well.

GMT800 2500hds with 6 liters have 410s... check your owners manual if you don't believe me. There is no optional axle ratio and wasn't throughout the run. I am talking 2500hd here.... not a 2500 light duty, not a 1500hd... Now GMT900s changed that. And yes since its a GMT900 the op has it has a 6L90E.

 

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Badass69 Senior Enthusiast

Badass69

Posted
Posted

New body style 07, tires are Michelin LT265/75R16's

 

60mph - 1750 rpm

70mph - 2000 rpm

 

Measured in 6th gear with the dash tach

Your truck has the 373s the truck says it came with. Indentical setup and rpm that my 09 2500hd did with 373's.

 

 

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Badass69 Senior Enthusiast

Badass69

Posted
Posted

My 2500hd came with the large receiver and 3.73 gears.

Mike

My 09 had the 2.5" receiever too. I believe that all 2500 hd and up trucks got the bigger receiver on the gmt900s. In fact I will just say they did.

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Man With A Gun Enthusiast

Man With A Gun

Posted
  • Author
Posted

So I guess this truck is going to get even worse mileage than I thought? LOL

 

Oh well... so long as it tows my 10,000 fifth wheel I'm picking up from my Uncle tomorrow morning, I can live with that. Thanks for the opinions and info

Carder09 Senior Enthusiast

Carder09

Posted
Posted

I just don't think you will see man HD truck's rolling around with 3.23 gears so yeah, low gas mileage but awesome towing.

chupe442 Enthusiast

chupe442

Posted
Posted

You have all the information that tells you what your truck came with on day 1 from the factory. The only way to know if the previous owner re-geared it is to get under there and see what you got. As for mileage and capacity... It will pull it and you will be getting even worse mileage. Have fun!

therink Enthusiast

therink

Posted
Posted

07 to 10 gasser Hds came standard with 3:73. 4:10 was available option. Same holds true for 11+ HD. I have owned three HD GM gasser since 05 and had to factory order all to get 4:10 axles.

 

You can run your VIN online (google) or ask any GM dealer to confirm which axle you have.

Silverado4x4 Senior Enthusiast

Silverado4x4

Posted
Posted

07 to 10 gasser Hds came standard with 3:73. 4:10 was available option. Same holds true for 11+ HD. I have owned three HD GM gasser since 05 and had to factory order all to get 4:10 axles.

 

You can run your VIN online (google) or ask any GM dealer to confirm which axle you have.

 

+1, your right on.

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