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2013 Silverado Axle and Differentials chart?

elric
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elric Enthusiast

elric

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Got some pics of my RPO codes, got a GU5 3.23 and G80. Fine. So is there a chart of axle models to RPOs? It rained last night, so I'm not crawling under my land yacht to get the tags or stamped codes just right now... Who made the axles?

 

My L20 4.8L runs sweet, but my WT has the tow package. Struggles to hit 20mpg, and that hurts when gas is $3.50+ a gallon. BIG fuel tank.

elric Enthusiast

elric

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Had to get my plates renewed at local DMV... So I had to open up my Silverado anyways. Crawled under rear, could not see stamped numbers or tags. It is a ten bolt, for whatever good that does... No front axle, not really needed on a 2WD [CPT Obvious]

Silverado_Differential.jpg

swathdiver Senior Enthusiast

swathdiver

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The axles were made by AAM (American Axle and Machine) and are Saginaw 8.6" or 9.5" on the 1500 GMT900s.

 

The G80 RPO code denotes that it is equipped with the locking limited slip carrier.

 

The ring and pinion ratios used in the 8.6" were:

GU4    3.08
GU5    3.23
GU6    3.42
GT4    3.73
GT5    4.10

 

The latter 3 ratios could be had in the 9.5" 15-Bolt semi-floater.  This axle was used behind the RWD and 4x4 pickups and SUVs with the L76 6.0 engine from 2007-2009 and the L92/L9H/L94 6.2 engines from 2007-2014.  An AWD Denali or Escalade will have the 8.6" axle out back.

 

A change in ratios might help city driving or highway mileage depending on which you select.  A numerically higher ratio will help with stop and go city driving, the lower numbers will help on the highway.  In my opinion in the case for the 4.8 with a 4-speed, you really don't want anything steeper than 3.73s.

 

Right now you're turning about 1,727 rpms without converter slippage on stock 265-70-17s.  3.42 would increase this to 1,826 rpms and 3.73s to 1,992 rpms.

 

It will likely takes years to recover the cost.  We pay more in fuel compared with new cars but for the most part, don't have a car payment anymore.
 

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elric Enthusiast

elric

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I was unable to contort myself to look on top of the axle for any codes. From looking at the stuff on the internet, I thought it would be an 8.5 , but I most certainly lack any experience in the axle and diff combinations.

newdude Senior Enthusiast

newdude

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2007-2013 1500s.

 

Unless its an NHT truck (max trailer) or a 6.2 or 6.0 Vortec Max, all of the other combos use the 8.625" axle.

 

NHT, Vortec Max and 6.2 use the 9.5" axle.  

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swathdiver Senior Enthusiast

swathdiver

Posted
Posted (edited)
On 9/26/2023 at 11:07 AM, elric said:

I was unable to contort myself to look on top of the axle for any codes. From looking at the stuff on the internet, I thought it would be an 8.5 , but I most certainly lack any experience in the axle and diff combinations.

The 8.5" was beefed up sometime in the 1990s for truck use, they added an 1/8" to the ring gear and called it an 8.6".  Very similar 10-bolt housing as used in the 1980s, such as on the Buick Grand National.

 

Your RPO codes are in the glovebox.

Edited by swathdiver

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