Rear Differential Service Questions

mbowman · June 11, 2009

Hello. I read the tech wiki but could not find the information that I was looking for.

I have an 08 Silverado Z71, 3.73 with G80.

I am planning on changing the rear diff fluid. I went to the local dealer and got a new gasket, but I am not 100% sure they gave me the right one.

GM Part Number 15807693

Also does anyone know the torque spec for the cover bolts?

Thanks

Martin

gvbhunt · June 11, 2009

Does your truck have the 9.5" rear end? If so it has a drain plug and you don't need to pull the cover.

mbowman · June 11, 2009

Good question on the rear end size, not sure!

There is no drain plug, just a fill plug on the cover. I want to remove the cover and clean the magnet etc. I did the front yesterday and there were some filings on the the drain plug magnet.

Martin

gvbhunt · June 11, 2009

Ok, according to the Service Manual, it looks like the cover bolts are 30 lb ft. Also I can find nothing about a gasket for the cover. I had heard that they may have one built into the cover. I have also heard to just use RTV or something like that. Hope that helps.

mbowman · June 11, 2009

Ok, according to the Service Manual, it looks like the cover bolts are 30 lb ft. Also I can find nothing about a gasket for the cover. I had heard that they may have one built into the cover. I have also heard to just use RTV or something like that. Hope that helps.

Thanks for the information. I think that I will be getting oily tonight ;-)

Martin

gvbhunt · June 11, 2009

It also says the fill plug is 24 lb ft. Just FYI.

2005LT · June 11, 2009

Let us know what the fluid looks like after you drop it. How much mileage do you have on your 08 so far Martin?

MS3DALE · June 11, 2009

I went to the local dealer and got a new gasket, but I am not 100% sure they gave me the right one.

GM Part Number 15807693

Thats the correct part number for the 8.5"/8.625" rear-end.

26063649 would be for the 9.5" rear-end

slomo007 · June 11, 2009

There is a gasket, just not sure of the part #, I got a replacement from Autozone. I used the gasket and some RTV (though use this sparingly if you are are using a synthetic fluid - supposedly the fluid can break down the RTV).

I replaced my rear diff fluid at about 15k miles and am glad I did....it was pretty nasty.

MS3DALE · June 11, 2009

There is a gasket, just not sure of the part #

15807693 for the 8.5"/8.625" rear-end

mbowman · June 11, 2009

I am right around 15K miles. I did the front yesterday, there was some metal shavings on the drain plug and I think that there must have been some water in the fluid as it was slightly milky, not much though.

I will do the rear tonight and post back.

I am also going to pain the rear cover, the paint is flaking and showing some rust. WTF is all that about!!!

Thanks all

Martin

Rons05z71 · June 12, 2009

I think you can only use synthetic in the rear end. 75w-90??? I just did it the other night. I didnt replace the gasket though. its a hard garlock type of gasket on mine. My owners manual says only synthetic in the rear

pm26 · June 12, 2009

I

I am also going to pain the rear cover, the paint is flaking and showing some rust. WTF is all that about!!!

Sounds a bit painful.

Yes, these covers are just stamped sheet metal and they do not paint them well. I need to repaint mine as well.

Ryan00TJ · June 12, 2009

I am right around 15K miles. I did the front yesterday, there was some metal shavings on the drain plug and I think that there must have been some water in the fluid as it was slightly milky, not much though.

I will do the rear tonight and post back.

I am also going to pain the rear cover, the paint is flaking and showing some rust. WTF is all that about!!!

Thanks all

Martin

I changed my F @ R diffs at around 3K miles. My front oil was also somewhat gray colored and milky. Not like it had been water contaminated. I used to offroad alot and know what water intrusion looks like. I used Mobil 1 Synthetic 75W90 front and rear. I used Permatex black RTV on the rear gasket surface and 2 months later it started to leak. Nothing bad, just 5-10 drips a week. I plan to fix it soon and replace with a GM gasket. I've never had problems with M1 SYN and RTV before. I've probably done 10-15 diffs this way. Everything was clean, 1/4" bead RTV, 2 hours dry before oil, etc....

I agree about GM's underbody paint job. Pretty shoddy. I guess rust is cool....