How do I determine the exact model of my front differential?

[Mr T]

Folks:

This Saturday I'm going to have my 2008 Denali XL, that has 192K miles, up in the air to listen and look for the cause of rotating noise when it is under power. I think the front differential or transfer case is the culprit. Both front hub assemblies have been replaced in the past year and this only hums when under power.

Anyway, I was looking up the price or front diff. replacement, just to prepare the budget for IMPACT. Well, I noticed there are a few different models I could pick from. Re-manufactured, of course.

Does the door tag tell me what ratio my front and rear are at? I know they have to be the same; just want to be able to shop for the right unit. The tag has the VIN number, of course, and also Model number as K10906.

I believe it diffs have to be either the 3.73 or 4.10 RATIO.

Thoughts?

 

[swathdiver]

Trevor, your Denali has 3.42 gears. Your front axle is 8.25" and referred to as a clamshell design. AAM makes it. www.demandaam.com

You probably just need a bearing replaced, going to tackle the job yourself? There are some good write ups on here.

 

[OR VietVet]

If the rear axle is a 3.73 the code would be GS3 and GT5 for 4.10 gear ratio. You can match from there. It may be a different ratio so you should just google the RPO codes for your rig and see what ratio you have.

 

[wjburken]

Folks:

This Saturday I'm going to have my 2008 Denali XL, that has 192K miles, up in the air to listen and look for the cause of rotating noise when it is under power. I think the front differential or transfer case is the culprit. Both front hub assemblies have been replaced in the past year and this only hums when under power.

Anyway, I was looking up the price or front diff. replacement, just to prepare the budget for IMPACT. Well, I noticed there are a few different models I could pick from. Re-manufactured, of course.

Does the door tag tell me what ratio my front and rear are at? I know they have to be the same; just want to be able to shop for the right unit. The tag has the VIN number, of course, and also Model number as K10906.

I believe it diffs have to be either the 3.73 or 4.10 RATIO.

Thoughts?

Look at the RPO sticker in your glove box and see what you have for G codes. My guess is you will see GU6 which is a 3.42 ratio.

 

[Mr T]

Trevor, your Denali has 3.42 gears. Your front axle is 8.25" and referred to as a clamshell design. AAM makes it. www.demandaam.com

You probably just need a bearing replaced, going to tackle the job yourself? There are some good write ups on here.

Swathdiver: I would rather tackle it myself. I know how to remove the diff. I had to drop it when I replaced the o-ring on the oil pump pickup tube. I don't have a press to press the bearing from the race, but have access to one. I know that would save me a LOT of cash over buying a whole new assembly--which would be a waste. I've changed the gear oil every 30K, so I'd be shocked the spline and other gears are gone. All the oil that was removed was "normal", if you will. I too think it is likely just one of the bearings going out. I would probably just replace both while in there.

I do wish I had a comprehensive list of special tools I would need. I have the usual that let me do hub replacements, break jobs, o-ring replacement, shock replacements, etc, etc.... Just worried I will need other special tools to pull bearings loose.

So I'm getting ahead of myself as I don't know for sure if that is the issue (noise) but will determine that this week end. In the mean time, I looked at the link you provided and got to this page:

http://www.demandaam.com/product-catalog/installation-parts-and-kits/master-bearing-kits

half way down is 74067005. Looks like the bearings I would likely need. Is that what you were thinking?

 

[Mr T]

Look at the RPO sticker in your glove box and see what you have for G codes. My guess is you will see GU6 which is a 3.42 ratio.

Wow, first time I've looked at one of these. Lot's of 3 dig codes. There is a GU6 and G69 and G80. So your guess looks to be correct.

 

[OR VietVet]

Yea, the G80 means positraction/limited slip.

G69 is auto air level control.

 

[wjburken]

Wow, first time I've looked at one of these. Lot's of 3 dig codes. There is a GU6 and G69 and G80. So your guess looks to be correct.

That sticker is the story of what your Yukon has. If you go out to www.gmc.com and click on the CHAT NOW box in the bottom right corner, they can send you the full build sheet for your vehicle if you provide the VIN number. It will list all the RPO codes for your vehicle and what they mean.

G69 is Auto Level Control - Air ride shocks in rear with Air Compressor
G80 is Locking rear differential

Both standard with the Denali package.

 

[swathdiver]

half way down is 74067005. Looks like the bearings I would likely need. Is that what you were thinking?

No! 74067004, your front differential is 8.25". In the picture of that one, I was thinking the two that are #6 or one not shown that is at the end of the fixed tube but what really do I know from over here? LOL

@Matthew Jeschke

Matt here rebuilt his a while back and did a great write up, slightly different, but good info.

 

[Mr T]

No! 74067004, your front differential is 8.25". In the picture of that one, I was thinking the two that are #6 or one not shown that is at the end of the fixed tube but what really do I know from over here? LOL

@Matthew Jeschke

Matt here rebuilt his a while back and did a great write up, slightly different, but good info.

I'll check out his write up.

On the AAM website I put in retailers who would sell that part set locally. It listed a company not too far from my home. I called them and within 2 min they had told me what I needed was the 8.25 as the 9.25 is for Dodge applications or GMC 3/4 ton and larger. They clearly knew their stuff. Apparently they rebuild transmissions and differentials on trucks for a daily business. They put me in contact with one of their line mechanics. He was a non-nonsense guy of 65. Said he had been rebuilding diffs since America build all the replacement parts Referenced sometime since the 70s. Anyway, he said it is something I could DIY, but there are two areas I need to be careful of (which I don't even recall). He then said my issue with my noise sounds like the bearing and not the internal gears (I would agree with him). However, he said he recommend a full rebuild and not gust bearings. Mostly because it has 192K on it. Said most don't make it that far and if he were to do bearings, we will likely have gear failure in another 10 to 20K or so and have to pull it from the car once more--and that's $150 to drop and put it back in.

I asked him for a quote and he said full rebuild--and him doing it--is $900 plus the $150 remove and remount it for a total of $1050. He did say he sees at least 2 or 3 of these a week and can do them with his eyes closed.

I'm leaning for them to do the full rebuild than me to yank it, press the bearings out and HOPE I do it right--to then have gears fail in the next year or so.

Am I crazy?

 

[OR VietVet]

I don't think you are crazy. I was in the repair business for 35+ years and I still would not attempt a full rebuild. I was just never taught. Bearing replacement can be simple or cause problems down the road. When you have something like those gears all settled in with the current set up and then mess with their "comfort zone" they can bite you. If you are going to keep the rig and want to depend on it and have a warranty, I would do it, but of course it is your call. I would also stress that they need to diagnose before tear down to verify EXACTLY what is the problem.

 

[Mr T]

I don't think you are crazy. I was in the repair business for 35+ years and I still would not attempt a full rebuild. I was just never taught. Bearing replacement can be simple or cause problems down the road. When you have something like those gears all settled in with the current set up and then mess with their "comfort zone" they can bite you. If you are going to keep the rig and want to depend on it and have a warranty, I would do it, but of course it is your call. I would also stress that they need to diagnose before tear down to verify EXACTLY what is the problem.

Yes, good point on proper diagnose. They suggest the first think is to pull the drain plug and look for shavings. My last oil change was 10K ago and if I recall had minor issues. My second step--I might make it the first, to be honest--is to get the rig on all 4 jack stands. Have someone put it in drive and rotate tires to about 25 to 30 mph. That is when I can hear it in the cab. Get underneath and use a pipe to press it against the front Diff then the transfer case. See which transmits the most noise. Hope that tells me where the low rpm noise is coming from. Interesting enough is it only makes the low rumbling when under power. If I put it in neutral when going 30mph on the road, the noise goes away. Back in drive and give it some gas and you hear it again.

 

[OR VietVet]

Buy a mechanics stethoscope for precise diagnosis for noises. Very inexpensive for max upgrade. The noise may not show if not under the load of the vehicle weight pulling down the road. See if you can do a "Mission Impossible" ride under there while a friend drives it down the street. Don't you dare take me seriously!!!!

 

[Mr T]

Buy a mechanics stethoscope for precise diagnosis for noises. Very inexpensive for max upgrade. The noise may not show if not under the load of the vehicle weight pulling down the road. See if you can do a "Mission Impossible" ride under there while a friend drives it down the street. Don't you dare take me seriously!!!!

LOL

I'll hire Tom Cruse. He's up for it!

 

[OR VietVet]

Yea, he brags about doing a lot of his own stunts. Call him on it.

 

[swathdiver]

I'll check out his write up.

On the AAM website I put in retailers who would sell that part set locally. It listed a company not too far from my home. I called them and within 2 min they had told me what I needed was the 8.25 as the 9.25 is for Dodge applications or GMC 3/4 ton and larger. They clearly knew their stuff. Apparently they rebuild transmissions and differentials on trucks for a daily business. They put me in contact with one of their line mechanics. He was a non-nonsense guy of 65. Said he had been rebuilding diffs since America build all the replacement parts Referenced sometime since the 70s. Anyway, he said it is something I could DIY, but there are two areas I need to be careful of (which I don't even recall). He then said my issue with my noise sounds like the bearing and not the internal gears (I would agree with him). However, he said he recommend a full rebuild and not gust bearings. Mostly because it has 192K on it. Said most don't make it that far and if he were to do bearings, we will likely have gear failure in another 10 to 20K or so and have to pull it from the car once more--and that's $150 to drop and put it back in.

I asked him for a quote and he said full rebuild--and him doing it--is $900 plus the $150 remove and remount it for a total of $1050. He did say he sees at least 2 or 3 of these a week and can do them with his eyes closed.

I'm leaning for them to do the full rebuild than me to yank it, press the bearings out and HOPE I do it right--to then have gears fail in the next year or so.

Am I crazy?

Nope. I get my immense satisfaction doing my own repairs but sometimes its best to turn a project over to pros. Seems as if you've hit a gold mine in finding a good shop close by with competent hands. Tough call.

 

[ivin74]

Swathdiver: I would rather tackle it myself. I know how to remove the diff. I had to drop it when I replaced the o-ring on the oil pump pickup tube. I don't have a press to press the bearing from the race, but have access to one. I know that would save me a LOT of cash over buying a whole new assembly--which would be a waste. I've changed the gear oil every 30K, so I'd be shocked the spline and other gears are gone. All the oil that was removed was "normal", if you will. I too think it is likely just one of the bearings going out. I would probably just replace both while in there.

I do wish I had a comprehensive list of special tools I would need. I have the usual that let me do hub replacements, break jobs, o-ring replacement, shock replacements, etc, etc.... Just worried I will need other special tools to pull bearings loose.

So I'm getting ahead of myself as I don't know for sure if that is the issue (noise) but will determine that this week end. In the mean time, I looked at the link you provided and got to this page:

http://www.demandaam.com/product-catalog/installation-parts-and-kits/master-bearing-kits

half way down is 74067005. Looks like the bearings I would likely need. Is that what you were thinking?

I rebuilt the front diff on my rig for less than $200 bucks and that include buying some special tools. I did not have to use a press for anything.

 

[Mr T]

I rebuilt the front diff on my rig for less than $200 bucks and that include buying some special tools. I did not have to use a press for anything.

Did you rebuild all of it or just replace the carrier bearings?

 

[swathdiver]

I rebuilt the front diff on my rig for less than $200 bucks and that include buying some special tools. I did not have to use a press for anything.

Ah, I remember now that you did too! Didn't you do a thread on this as well?

 

[ivin74]

Did you rebuild all of it or just replace the carrier bearings?

Yes, I rebuilt the entire diff.

Ah, I remember now that you did too! Didn't you do a thread on this as well?

You are correct, I posted the rebuild somewhere on this site.