Time For Differential & Transfer Case Service.

[overlord1]

I've got just over 10K on my '06 Silverado and figured it would be a good time for the first service on the differentials and transfer case. If I'm understanding the owner's manual correctly, I should fill the front diff. and transfer case until the new oil comes out the fill hole. Is this correct? The rear diff fluid should be 1/2" below the fill hole as I understand it. What are the recommended torque specs for the front diff and transfer case plugs? Several posts indicated 30 ft/lbs for the rear diff. cover bolts but I couldn't find any info on the torque for the front diff. and transfer case plugs. Lastly, should I engage the 4WD system for a mile or two to warm up the fluid in the front diff. and transfer case prior to draining these fluids or are the gears still engaged in the front diff. even when in 2WD? Thanks in advance!

[Dave in Mpls]

Front Differential-

The fluid level should be at the bottom of the filler plug hole at operating temp. I fill it to the bottom of the hole, take it for a spin with the front differential engaged, then remove the fill plug and let any excess drain out, which is minimal. The factory spec fluid for the front diff is dino 80W-90 gear lube. I personally run 75W-90 Mobil 1 synthetic (same as rear). There is a TSB floating around out there that suggests changing out the front diff vent if it is currently black in color if running synthetic. Search the forum for 03-04-19-001B. The published capacity of the 8.25" front diff is 1.75 quarts. The torque specs for both the drain and fill plugs are 24 ft-lbs.

 

Rear differential-

I'm 99% positive the recommended fluid height is 5/8" to 1 5/8" below the fill hole for the '06 8.6" rear diff. Verify the level in your owners manual. The factory spec fluid for the rear diff is synthetic 75W-90 gear lube meeting GM spec 9986115. I, along with MANY others, run 75W-90 Mobil 1 synthetic in the rear with no ill effects. If your truck is equipped with the G80 locking rear (which I assume it is), you will NOT need any additional friction modifier with the Mobil 1. The published capacity of the 8.6" rear diff is 2.15 quarts. The torque specs for the cover bolts are 30 ft-lbs and for the fill plug is 24 ft-lbs. There are many schools of thought regarding sealing the rear cover. I use a new gasket with a thin coat of aviation form-a-gasket on both sides. Whichever method you use, make sure all the old gakset material is removed from both the rear end and cover. Also be sure to clean any material off the magnet.

 

Transfer Case-

Assuming your Z-71 has the Auto4x4 transfer case (RPO NP8), the fluid level should be to the bottom of the hole. ONLY use GM AutoTrak II in the TC. Some suggest changing the drain and fill plugs while serviceing the TC. I personally just clean up the threads with a soft wire brush (to remove factory-applied thread sealer) and re-apply a thin coat of thread sealer. The published capacity of the TC is 2 quarts, but it should take just shy of that. The torque specs for both the drain and fill plugs are 15 ft-lbs.

 

I suggest buying a quart size pump - really makes filling the front diff and TC easy!

 

I think running in 4x for a short distance is a good idea, as it will warm up the lube, as well as suspend any particulates.

[overlord1]

Front Differential-

The fluid level should be at the bottom of the filler plug hole at operating temp. I fill it to the bottom of the hole, take it for a spin with the front differential engaged, then remove the fill plug and let any excess drain out, which is minimal. The factory spec fluid for the front diff is dino 80W-90 gear lube. I personally run 75W-90 Mobil 1 synthetic (same as rear). There is a TSB floating around out there that suggests changing out the front diff vent if it is currently black in color if running synthetic. Search the forum for 03-04-19-001B. The published capacity of the 8.25" front diff is 1.75 quarts. The torque specs for both the drain and fill plugs are 24 ft-lbs.

 

Rear differential-

I'm 99% positive the recommended fluid height is 5/8" to 1 5/8" below the fill hole for the '06 8.6" rear diff. Verify the level in your owners manual. The factory spec fluid for the rear diff is synthetic 75W-90 gear lube meeting GM spec 9986115. I, along with MANY others, run 75W-90 Mobil 1 synthetic in the rear with no ill effects. If your truck is equipped with the G80 locking rear (which I assume it is), you will NOT need any additional friction modifier with the Mobil 1. The published capacity of the 8.6" rear diff is 2.15 quarts. The torque specs for the cover bolts are 30 ft-lbs and for the fill plug is 24 ft-lbs. There are many schools of thought regarding sealing the rear cover. I use a new gasket with a thin coat of aviation form-a-gasket on both sides. Whichever method you use, make sure all the old gakset material is removed from both the rear end and cover. Also be sure to clean any material off the magnet.

 

Transfer Case-

Assuming your Z-71 has the Auto4x4 transfer case (RPO NP8), the fluid level should be to the bottom of the hole. ONLY use GM AutoTrak II in the TC. Some suggest changing the drain and fill plugs while serviceing the TC. I personally just clean up the threads with a soft wire brush (to remove factory-applied thread sealer) and re-apply a thin coat of thread sealer. The published capacity of the TC is 2 quarts, but it should take just shy of that. The torque specs for both the drain and fill plugs are 15 ft-lbs.

 

I suggest buying a quart size pump - really makes filling the front diff and TC easy!

 

I think running in 4x for a short distance is a good idea, as it will warm up the lube, as well as suspend any particulates.

 

Thanks Dave! I really appreciate the detailed response. That is just the information I was looking for.

[Dave in Mpls]

No problem, Ed

 

A couple other things to add....

 

If your front diff vent cover is white (which it should be in an '06), you are good to go with synthetic in the front diff.

 

Also, an allen wrench of the correct length makes checking the level in the rear diff easy. There is plenty of room to fill the rear diff directly from the bottles.

 

P.S. Being your truck is still under warranty, you may want to consider using the recommended GM fluid in the rear. The only downside to the GM fluid is the price.....about $25/quart!!!

 

Regards

[cmoore74]

Dave, I hear what you're saying, but as long as it meets the GL-5 specs I don't see how GM could void your warranty. Wouldn't that be like saying you could only use the exact brand of motor oil GM uses as a factory fill otherwise they would void your warranty?

 

I'm about to change mine and I'm going with Amsoil sever gear oil 75W90 which meets the GL-5 spec required by GM. I believe the Mobil 1 75W90 also meets this spec and I'm sure there are others.

 

This is the specs listed by Amsoil for this gear oil:

 

Recommended for use in differentials, manual transmissions and other gear applications requiring any of the following specifications: API GL-5, MT-1, MIL-PRF-2105E, Dana SHAES 234 (Formerly Eaton PS-037), Mack GO-J, or the differential (hypoid) gear oil specifications from all domestic and foreign manufacturers such as GM, Ford and Daimler Chrysler. Can also be used in axles where an API GL-4 lubricant is recommended.

 

 

I just didn't want to pay the insane price GM is charging for their gear oil.

 

Please don't turn this into a brand war...

[Dave in Mpls]

Dave, I hear what you're saying, but as long as it meets the GL-5 specs I don't see how GM could void your warranty. Wouldn't that be like saying you could only use the exact brand of motor oil GM uses as a factory fill otherwise they would void your warranty?

 

I'm about to change mine and I'm going with Amsoil sever gear oil 75W90 which meets the GL-5 spec required by GM. I believe the Mobil 1 75W90 also meets this spec and I'm sure there are others.

 

This is the specs listed by Amsoil for this gear oil:

 

Recommended for use in differentials, manual transmissions and other gear applications requiring any of the following specifications: API GL-5, MT-1, MIL-PRF-2105E, Dana SHAES 234 (Formerly Eaton PS-037), Mack GO-J, or the differential (hypoid) gear oil specifications from all domestic and foreign manufacturers such as GM, Ford and Daimler Chrysler. Can also be used in axles where an API GL-4 lubricant is recommended.

 

 

I just didn't want to pay the insane price GM is charging for their gear oil.

 

Please don't turn this into a brand war...

 

 

Chris-

 

The rear axle fluid "must" meet GM spec 9986115. Both Mobil and Amsoil openly admit their fluids do NOT currently meet the GM spec. Royal Purple claims to meet it. However, I have only been able to verify this verbally, and have never seen anything in writing to confirm.

 

God only knows what makes GM 9986115 so special....perhaps the additive package that gives it that nice grape smell!!

[RyanbabZ71]

When doing the tcase find a parking lot and do some figure 8's

[overlord1]

I've been considering getting an aftermarket aluminum differential cover for the rear that has a drain plug. Figured this would make future fluid changes quick and easy. Can someone confirm that the diff. cover bolts on an '06 Silverado are Metric?

[Mighty HD]

tag...this should get good.

[frdfandc]

Why the differential and t-case services so soon??????

 

Last time I heard of these services this soon was due to SEVERE driving habits. So unless you are constantly off-roading, there really isn't a need to service the diffs and t-case so soon.

[overlord1]

Why the differential and t-case services so soon??????

 

Last time I heard of these services this soon was due to SEVERE driving habits. So unless you are constantly off-roading, there really isn't a need to service the diffs and t-case so soon.

 

I do a lot of driving in sand (practically every weekend) since I am only a few minutes from the beach and have access to 4X4 vehicle only areas. Plus I have towed a heavy trailer on a few occassions so I want to make sure to get any metal shavings out.

[frdfandc]

Gotcha.

[cmoore74]

Dave, I hear what you're saying, but as long as it meets the GL-5 specs I don't see how GM could void your warranty. Wouldn't that be like saying you could only use the exact brand of motor oil GM uses as a factory fill otherwise they would void your warranty?

 

I'm about to change mine and I'm going with Amsoil sever gear oil 75W90 which meets the GL-5 spec required by GM. I believe the Mobil 1 75W90 also meets this spec and I'm sure there are others.

 

This is the specs listed by Amsoil for this gear oil:

 

Recommended for use in differentials, manual transmissions and other gear applications requiring any of the following specifications: API GL-5, MT-1, MIL-PRF-2105E, Dana SHAES 234 (Formerly Eaton PS-037), Mack GO-J, or the differential (hypoid) gear oil specifications from all domestic and foreign manufacturers such as GM, Ford and Daimler Chrysler. Can also be used in axles where an API GL-4 lubricant is recommended.

 

 

I just didn't want to pay the insane price GM is charging for their gear oil.

 

Please don't turn this into a brand war...

 

 

Chris-

 

The rear axle fluid "must" meet GM spec 9986115. Both Mobil and Amsoil openly admit their fluids do NOT currently meet the GM spec. Royal Purple claims to meet it. However, I have only been able to verify this verbally, and have never seen anything in writing to confirm.

 

God only knows what makes GM 9986115 so special....perhaps the additive package that gives it that nice grape smell!!

 

 

Dave,

 

Could it be that once Amsoil severe gearoil didn't meet the spec and now it does? According to the Amsoil web-site they list the 75W90 Severe Gear oil under the application guide and they have a foot-note stating "Synthetic lubricant, GM part no. 12378261, specification No. 9986115." I must admit the way it's listed on the Amsoil site is very confusing. I figured the GL-5 spec was the same as GM spec 9986115.

 

Just trying to figure out if I bought 3 qts for nothing. I suppose I could hold onto is and use it to change out the front diff when that's ready.

 

I definitely would rather spend the few extra $ on the GM grape stuff than take a chance that it could void the warranty if something were to happen.

 

Maybe Nick the Amsoil distributor could chime in?

 

I sent an e-mail off to Amsoil asking if the oil meets the GM spec. I'll post when I get a response in case anyone else is curious.

 

Chris

[overlord1]

Chris,

I too am planning to use the Amsoil Severe Gear lube in the front and rear diff. As a matter of fact I picked up 6 quarts from Nick last week. I too had assumed that the Amsoil product met the GM specs as I had not heard info to the contrary. Maybe Nick or someone else can confirm that it does meet the specs?

[cmoore74]

Still waiting on a reply from Amsoil, but I found this:

 

http://www.thedieselpageforums.com/tdpforu...hp/t-18728.html

 

The post is a bit old, but Eaton (maker of the G80 locker for GM) says as long as it meets the GL-5 spec you should be OK. Not sure if that is proof enough to GM if something were to happen to the rear diff and they tried to void the warranty.

 

Maybe I'll just buy the over-priced GM stuff for the 1st change. After that it would be out of warranty for subsequent changes and I haven't heard of any problems caused using any of the other GL-5 spec synthetics.