2004 GMC 3500 rear end size question - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**67sss** · 09-24-2021, 10:34 AM

Pulled my Vin number and decoded the options. I know I have a 3:73 rear-end ratio. How do I tell what size rear-end I have? 9.5, 10.5 or 11.5? I'm getting ready to replace the parking brake pads and a axle seal. Tia

**hatzie** · 09-24-2021, 03:46 PM

Won't be a 9.5 in a 3500 You can tell right away if you have one of these by looking. The other two axles are full floating so the hubs extend out from the wheel with the bolts holding in the axle shaft. The 9.5 is a C Clip axle like the 10 bolt and 12bolt.

LQ4 gasoline will have the 10.5

The dirtymax will have the 11.5

Not sure about the 8.1L They came with the Allison so it might have an 11.5 out back.

**Richard** · 10-03-2021, 07:03 PM

An easy tell for an 11.5 is that the pinion will have a damper on it. Looks like a harmonic balancer. I know the 11.5 came in 2500HD's I have seen. My swap rear end is from one. I would wager an 11.5.

95 S_Trucker · 10-04-2021, 11:01 AM

You have an 11.5". The only way it could be a 10.5 is if the truck was a SRW with a 6.0. But the 6.0 trucks had 4.10 ratio. So, since your truck has 3.73, we can tell you have an 8.1 or 6.6. So you have an 11.5".

**67sss** · 10-25-2021, 06:13 PM

Thanks for the help! 11.5" it is. Just replaced inner and outer bearings, seals, parking brake pads and changed rear diff fluid. I seem to have a "bounce" coming from somewhere. Shocks are new all the way around. Wondering if the carrier bearing is starting to go out? The best way to describe the "bounce" is after going over a rough road, it seems like the truck suspension feels like I'm driving over washboard. Probably will replace the u-joints and the carrier bearing to see if that helps. Any other suggestions are appreciated.

09-24-2021, 10:34 AM	#1
67sss Registered User Join Date: Nov 2002 Location: Mt. Vernon, WA.. Posts: 2,325	2004 GMC 3500 rear end size question Pulled my Vin number and decoded the options. I know I have a 3:73 rear-end ratio. How do I tell what size rear-end I have? 9.5, 10.5 or 11.5? I'm getting ready to replace the parking brake pads and a axle seal. Tia

09-24-2021, 03:46 PM	#2
hatzie Moderator Join Date: Oct 2008 Location: Wentworth, NH Posts: 4,977	Re: 2004 GMC 3500 rear end size question Won't be a 9.5 in a 3500 You can tell right away if you have one of these by looking. The other two axles are full floating so the hubs extend out from the wheel with the bolts holding in the axle shaft. The 9.5 is a C Clip axle like the 10 bolt and 12bolt. LQ4 gasoline will have the 10.5 The dirtymax will have the 11.5 Not sure about the 8.1L They came with the Allison so it might have an 11.5 out back. __________________ 1959 M35A2 LDT465-1D SOLD 1967 Dodge W200 B383, NP420/NP201 SOLD 1969 Dodge Polara 500 B383, A833 SOLD 1972 Ford F250 FE390, NP435/NP205 SOLD 1976 Chevy K20, 6.5L, NV4500/NP208 SOLD 1986 M1008 CUCV SOLD 2000 GMC C2500, TD6.5L, NV4500 2005 Chevy Silverado LS 2500HD 6.0L 4L80E/NP263 2009 Impala SS LS4 V8 RTFM... GM Parts Books, GM Schematics, GM service manuals, and GM training materials... 1973-1991 GM Light Truck Service, Unit/Overhaul, Wiring Manuals, Parts Books and Some 1968-1999 GM Service Training textbooks in PDF 1988-1998 GMT400 CK service manual project 1988-1993 GMT400 CK parts books. 1967-1972 GM Light, Medium, & Heavy Truck Service Manuals in PDF Please include at least the year and model in your threads. It'll be easier to answer your questions. And please let us know if and how your repairs were successful.

10-03-2021, 07:03 PM	#3
Richard Senior Member Join Date: Dec 1999 Location: Southern California Posts: 2,889	Re: 2004 GMC 3500 rear end size question An easy tell for an 11.5 is that the pinion will have a damper on it. Looks like a harmonic balancer. I know the 11.5 came in 2500HD's I have seen. My swap rear end is from one. I would wager an 11.5. __________________ Richard 1972 K10 Custom Deluxe SWB Fleetside My build https://67-72chevytrucks.com/vboard/...d.php?t=800746 Last edited by Richard; 10-03-2021 at 07:11 PM.

10-04-2021, 11:01 AM	#4
95 S_Trucker Registered User Join Date: Oct 2009 Location: . Posts: 2,187	Re: 2004 GMC 3500 rear end size question You have an 11.5". The only way it could be a 10.5 is if the truck was a SRW with a 6.0. But the 6.0 trucks had 4.10 ratio. So, since your truck has 3.73, we can tell you have an 8.1 or 6.6. So you have an 11.5".

10-25-2021, 06:13 PM	#5
67sss Registered User Join Date: Nov 2002 Location: Mt. Vernon, WA.. Posts: 2,325	Re: 2004 GMC 3500 rear end size question Thanks for the help! 11.5" it is. Just replaced inner and outer bearings, seals, parking brake pads and changed rear diff fluid. I seem to have a "bounce" coming from somewhere. Shocks are new all the way around. Wondering if the carrier bearing is starting to go out? The best way to describe the "bounce" is after going over a rough road, it seems like the truck suspension feels like I'm driving over washboard. Probably will replace the u-joints and the carrier bearing to see if that helps. Any other suggestions are appreciated.



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