2008 Sierra Denail 2wd - Differential Ring Gear Size?

GMC_SD_08 · December 12, 2009

I have a 2008 Sierra Denali 2WD and was looking at a website that showed either a 8.25 or 9.25 Ring Gear for Front Differential and 8.6 or 9.5 Ring Gear for Rear Differential. How can I confirm what size my truck has? I can get to the RPO codes and of course VIN just wasn't sure how or where to determine the correct sizes using those codes. If you have the information thanks in advance for sharing or if you have a website that I can use to look up please let me know.

I am looking to change my differential fluids and noticed they had different capacities based on the size differences. Some curiousity but also want to make sure I put in the correct amounts. Thanks in advance.

Badass69 · December 12, 2009

I have a 2008 Sierra Denali 2WD and was looking at a website that showed either a 8.25 or 9.25 Ring Gear for Front Differential and 8.6 or 9.5 Ring Gear for Rear Differential. How can I confirm what size my truck has? I can get to the RPO codes and of course VIN just wasn't sure how or where to determine the correct sizes using those codes. If you have the information thanks in advance for sharing or if you have a website that I can use to look up please let me know.

I am looking to change my differential fluids and noticed they had different capacities based on the size differences. Some curiousity but also want to make sure I put in the correct amounts. Thanks in advance.

There is an easy method that is sure fire. Just count the number of bolts attaching the rear cover on the differential. However for simplicity sake. Your truck has the 9.5" 14 bolt SF rear diff and being you have a 2wd you don't have a front differential at all.

Nytemare · December 12, 2009

ring gear depends on the rearend you have...

basically....if you have 6 lugs on your wheels you have an 8.6" gear

If you have 8 lugs you have the 9.5"

Oh as for the diff fluid...you pour it in till it comes out the hole...thats how you know its full.

Matt_ · December 12, 2009

ring gear depends on the rearend you have...
basically....if you have 6 lugs on your wheels you have an 8.6" gear

If you have 8 lugs you have the 9.5"

Not exactly...... 6 Lug trucks can have the 9.5" rear too... I believe this started again in 2006 with the "Max Trailering Package" as well for trucks with the 6.0L. There are a few other 6-lug trucks that have had the 6-lug 9.5" as well, i think the Silverado SS was one of them.

To the OP, i'm pretty sure the 2008 2WD Denali has the 9.5" ring gear. As others have said, count the number of bolts holding on the diff cover.

10 bolts = 8.6"

14 bolts = 9.5" for your truck

Badass69 · December 12, 2009

ring gear depends on the rearend you have...

basically....if you have 6 lugs on your wheels you have an 8.6" gear

If you have 8 lugs you have the 9.5"

Nope. 6 Lug trucks have the 9.5" rear too... I believe this started again in 2006 with the "Max Trailering Package" as well for trucks with the 6.0L. There are a few other 6-lug trucks that have had the 6-lug 9.5" as well, i think the Silverado SS was one of them.

To the OP, i'm pretty sure the 2008 2WD Denali has the 9.5" ring gear. As others have said, count the number of bolts holding on the diff cover.

10 bolts = 8.6"

14 bolts = 9.5" for your truck

GM has had the 9.5" 14 bolt in the 6 lug flavor for over 2 decades. The diff was used in the old Light duty 3/4 ton with a 7200 lb GVW back late 80's. The differential has been around since the early 80's as well. It was even used with the 5X5" bolt pattern in the 454 SS pickups from 90-93. GM then changed things again around 94 or 95 ( previous to the 96 Vortec trucks) and put the 6 lug 14 bolt in the 1/2 tons again. Of course these were all 4 wheel drive trucks, except for 2 wheel drive 3/4 pickups and vans that had the 14 bolt as well.

Either way a Denali will have the 9.5" differential. The 8.6" 10 bolt would not stand up to the 6.2 or the towing capacity of that truck particularily well.....

Matt_ · December 12, 2009

Yeah I was talking about a 6-lug 9.5" rear being in a 1500 series light duty truck.... they've been in a lot of other things, including Vans for a looong time. From 99 through 2005 they were extremely rare in 1500s.

Not ALL Denali's have the 9.5". The GMT900 AWD version doesn't (probably because of the 60/40 distribution, the rear doesn't take as much of a beating... although I still think that's stupid on GM's part)

Badass69 · December 12, 2009

Yeah I was talking about a 6-lug 9.5" rear being in a 1500 series light duty truck.... they've been in a lot of other things, including Vans for a looong time. From 99 through 2005 they were extremely rare in 1500s.

Not ALL Denali's have the 9.5". The GMT900 AWD version doesn't (probably because of the 60/40 distribution, the rear doesn't take as much of a beating... although I still think that's stupid on GM's part)

So your truck has a 10 bolt in the back with disc brakes on it? I never paid to close of attention to the Denali's because I dislike AWD but I was sure they had 14 bolt rears in them. The 2wds do...... at least they are listed to have it.

Matt_ · December 12, 2009

Yup, mines a 10 bolt with disc brakes

Badass69 · December 12, 2009

Yup, mines a 10 bolt with disc brakes

Wow that's real sweet....... Gm deserves a pat on the back for doing that. Found a bunch of others bitching that their AWD Denali just has the 10 bolt. Either way, the OP's truck, being 2 wheel drive has the 14 bolt diff.

GMC_SD_08 · December 12, 2009

I have confirmed that my 2WD Denali has the 14 bolt diff. Thank you all for your inputs.

Changing topic slightly how hard is it to change the fluid in this diff to a synthetic? I saw the drain plug on the back side. Is it as basic as pumping out from this drain plug then refill to just under the drain hole level? Is it recommended to take all 14 bolts off and change/clean other components before switching to synthetic? I am not an expert and don't claim to have all the details but I am pretty handy if someone can give me any advice. Thanks again in advance.

Matt_ · December 12, 2009

I personally would take the diff cover off to get all of the old fluid and any particles out of there. Then put the diff cover back on using a gasket ($10 from the dealer) and refill with fluid of choice. The owners manual states the level to fill it to... i usually fill it so it's about 1/8" below the fill hole.

09Jimmy · December 13, 2009

I have confirmed that my 2WD Denali has the 14 bolt diff. Thank you all for your inputs.

Changing topic slightly how hard is it to change the fluid in this diff to a synthetic? I saw the drain plug on the back side. Is it as basic as pumping out from this drain plug then refill to just under the drain hole level? Is it recommended to take all 14 bolts off and change/clean other components before switching to synthetic? I am not an expert and don't claim to have all the details but I am pretty handy if someone can give me any advice. Thanks again in advance.

It already has synthetic in it. Drain plug should be on the bottom facing up, the fill hole is in the side. Fill it even with the bottom of the threads on the filler plug. If it doesn't have a drain hole you'll have to pull the cover off to drain it completely.

GMC_SD_08 · December 13, 2009

I personally would take the diff cover off to get all of the old fluid and any particles out of there. Then put the diff cover back on using a gasket ($10 from the dealer) and refill with fluid of choice. The owners manual states the level to fill it to... i usually fill it so it's about 1/8" below the fill hole.

After taking off the cover is there a chemical or anything you recommend to use for getting particles out if not can you elaborate on how to get these small particles out? I havent seen the inside of the diff before so I just want to make sure and understand. Thanks again.

09Jimmy · December 13, 2009

I personally would take the diff cover off to get all of the old fluid and any particles out of there. Then put the diff cover back on using a gasket ($10 from the dealer) and refill with fluid of choice. The owners manual states the level to fill it to... i usually fill it so it's about 1/8" below the fill hole.

After taking off the cover is there a chemical or anything you recommend to use for getting particles out if not can you elaborate on how to get these small particles out? I havent seen the inside of the diff before so I just want to make sure and understand. Thanks again.

The diff cover has a circular magnet glued to the inside. Any metal shavings will be stuck to it. Wipe it off but DO NOT use solvent to clean the inside of the diff cover. Solvent will disolve the glue that hold the magnet on, possibly allowing the magnet to migrate inside your diff.