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What Size Is My Ring Gear?!


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I have read many of the older posts and half of the responses are 10.5 and the other half is 11.5. I am ready to pull everything apart I just need to know which parts I need to get. I have a 2001 GMC Sierra 2500HD with an Allison Trans. Is there a tag I can look at somewhere? I know I have 4:10 gears. That is as far as my knowledge goes.

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I have read many of the older posts and half of the responses are 10.5 and the other half is 11.5. I am ready to pull everything apart I just need to know which parts I need to get. I have a 2001 GMC Sierra 2500HD with an Allison Trans. Is there a tag I can look at somewhere? I know I have 4:10 gears. That is as far as my knowledge goes.

 

In the all the vendor books I have, the 02 to present has the 11.5" gear assembly. There are 31 pinion splines on the 11.5" and 30 pinion splines on the 10.5" if you want to check that way.

 

I am 99.9% sure that you have the older 10.5" assembly,in your 01 truck.

 

Don't forget that if you remove the whole assembly out and just get the new bearings pressed in, you don't have to mess with the ring and pinion shims. This way your patterns will remain correct prior to removal.

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I have read many of the older posts and half of the responses are 10.5 and the other half is 11.5. I am ready to pull everything apart I just need to know which parts I need to get. I have a 2001 GMC Sierra 2500HD with an Allison Trans. Is there a tag I can look at somewhere? I know I have 4:10 gears. That is as far as my knowledge goes.

 

In the all the vendor books I have, the 02 to present has the 11.5" gear assembly. There are 31 pinion splines on the 11.5" and 30 pinion splines on the 10.5" if you want to check that way.

 

I am 99.9% sure that you have the older 10.5" assembly,in your 01 truck.

 

Don't forget that if you remove the whole assembly out and just get the new bearings pressed in, you don't have to mess with the ring and pinion shims. This way your patterns will remain correct prior to removal.

 

 

 

 

Got everything pulled apart last night. I have the 10.5 Ring Gear. So, I guess the rule about all 8.1's having an 11.5 rear end are wrong. Also noticed the rear end can be adjusted from side to side with the help of some sort of threaded cups on either side of the diff. I need to get a certain tool to be able to adjust them. Had a problem getting the yoke balancer off of the Pinion.The balancer kept trying to slide off of the yoke! I am sure this will throw it off balance. I need to find out if I can take this to a driveline shop and have it fixed or if will I need a new one. I am hoping to have it all done today. I will be back with an update this evening.

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I have read many of the older posts and half of the responses are 10.5 and the other half is 11.5. I am ready to pull everything apart I just need to know which parts I need to get. I have a 2001 GMC Sierra 2500HD with an Allison Trans. Is there a tag I can look at somewhere? I know I have 4:10 gears. That is as far as my knowledge goes.

 

In the all the vendor books I have, the 02 to present has the 11.5" gear assembly. There are 31 pinion splines on the 11.5" and 30 pinion splines on the 10.5" if you want to check that way.

 

I am 99.9% sure that you have the older 10.5" assembly,in your 01 truck.

 

Don't forget that if you remove the whole assembly out and just get the new bearings pressed in, you don't have to mess with the ring and pinion shims. This way your patterns will remain correct prior to removal.

 

 

 

 

Got everything pulled apart last night. I have the 10.5 Ring Gear. So, I guess the rule about all 8.1's having an 11.5 rear end are wrong. Also noticed the rear end can be adjusted from side to side with the help of some sort of threaded cups on either side of the diff. I need to get a certain tool to be able to adjust them. Had a problem getting the yoke balancer off of the Pinion.The balancer kept trying to slide off of the yoke! I am sure this will throw it off balance. I need to find out if I can take this to a driveline shop and have it fixed or if will I need a new one. I am hoping to have it all done today. I will be back with an update this evening.

 

 

That is interesting. I have yet to see a Duramax or 8.1L in a GMT800 not have an 11.5” ring gear. The 10.5” isn’t rated for the 8.1L (or Duramax) behind an Allison in an HD truck. Suburban or G-van with an 8.1L and 4L80E, yes….HD truck no. I would love to see a picture of your rear axle with the cover on it. Are you the original owner? If your 8.1L trucks indeed has a 10.5” I very seriously doubt it is original.

 

4296532632_867cf3ddf4.jpg

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  • 2 weeks later...
I have read many of the older posts and half of the responses are 10.5 and the other half is 11.5. I am ready to pull everything apart I just need to know which parts I need to get. I have a 2001 GMC Sierra 2500HD with an Allison Trans. Is there a tag I can look at somewhere? I know I have 4:10 gears. That is as far as my knowledge goes.

 

In the all the vendor books I have, the 02 to present has the 11.5" gear assembly. There are 31 pinion splines on the 11.5" and 30 pinion splines on the 10.5" if you want to check that way.

 

I am 99.9% sure that you have the older 10.5" assembly,in your 01 truck.

 

Don't forget that if you remove the whole assembly out and just get the new bearings pressed in, you don't have to mess with the ring and pinion shims. This way your patterns will remain correct prior to removal.

 

 

 

 

Got everything pulled apart last night. I have the 10.5 Ring Gear. So, I guess the rule about all 8.1's having an 11.5 rear end are wrong. Also noticed the rear end can be adjusted from side to side with the help of some sort of threaded cups on either side of the diff. I need to get a certain tool to be able to adjust them. Had a problem getting the yoke balancer off of the Pinion.The balancer kept trying to slide off of the yoke! I am sure this will throw it off balance. I need to find out if I can take this to a driveline shop and have it fixed or if will I need a new one. I am hoping to have it all done today. I will be back with an update this evening.

 

 

That is interesting. I have yet to see a Duramax or 8.1L in a GMT800 not have an 11.5" ring gear. The 10.5" isn't rated for the 8.1L (or Duramax) behind an Allison in an HD truck. Suburban or G-van with an 8.1L and 4L80E, yes….HD truck no. I would love to see a picture of your rear axle with the cover on it. Are you the original owner? If your 8.1L trucks indeed has a 10.5" I very seriously doubt it is original.

 

4296532632_867cf3ddf4.jpg

 

 

 

Sorry for the delay. My truck DOES have an 11.5" Ring Gear. No doubt about it. After pulling everything apart, I measured and counted splines. I will say this, it is not a do it yourself job. You need someone with the knowledge of adjusting everything to fit just right. Thanks to all for the help!

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  • 11 months later...
4296532632_867cf3ddf4.jpg

 

 

The pics above seem odd to me. Why is the ring gear on the right side of the pinion gear on the 10.5"? Every vehicle I have seen has the ring gear on the left side of the pinion gear. Having it on the right side means the pinion is turning in the opposite direction to go foward.

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