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GM Tech (Cam)
GM Tech (Cam), GMC Mechanic
Category: GM
Satisfied Customers: 29355
Experience:  GM Grand Master Technician 2007. 14 years experience.
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I have a 2003 GMC Yukon XL and Id like to change the differential,

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I have a 2003 GMC Yukon XL and I'd like to change the differential, transfer case, and automatic transmission fluids. Is this a difficult job? How do I change the fluids?

Greetings and Welcome to Just answer.

The differentials and trasnfer case are VERY EASY.

the front diff and transer case have a drain plug but you need to remove the skid plates to get at them. The fluid in front diff is 80w90 synthetic at 2 quarts, and the transfer case is AutoTrac 2 fluid at 2 quarts.

There rear diff is not as easy.. For that you need to remove the rear cover and replace the gasket. Still not hard.

The transmission I would recommend having it flushed with a machine. IT will replace about 90% of the fluid where you taking the pan off does about 40%.




Customer: replied 6 years ago.

Is it difficult to remove the skid plates in the front?


How high do I fill the differentials and the transfer case?


What type of fluid and how much should I use in the rear differential?


Do I purchase a new gasket for the back or should I use some kind of gasket sealant or both?






No both skid plate are held on wigh 15mm bolts. the drain on the front diff is 13mm and the fill is 15mm.

The plugs on the transfer case are 18mm and do not over tighten them.

Use a new dry gasket as they are cheap and it take about 3 quarts of 80w90 synthetic.


Customer: replied 6 years ago.

Thanks, XXXXX XXXXX told me to use 75W90 synthetic for the differentials. What do you think?



That is just fine. In fact I often get the 2 confused, but the sylthetic is the important part.


Customer: replied 6 years ago.

OK, thanks. I will work on it this weekend and if all goes well, I will Accept your Answer.


I was reading through one manual that said I should fill the transfer case about 5/8" inch below the hole. Does that matter? Should I just fill everything up until the fluid runs out? Also, on the rear differential, what's the best way to open it up so that fluid doesn't flow all over the place?


I am having the shop flush the transmission fluid today. When I was driving up a mountain road the other day, the HOT TRANSMISSION warning message came on. Do you know if this happens often?





I fill all to the bottom of the hole.


The rear case, you take the bolts out of the bottom of the rear cover and with a pan under it, use a screwdriver to pry the cover off slowly at the bottom and that will help control the fluid.

I will be around this weekend to reply if you need any help.


As a couple tips, first lift the back end but support it from the frame not the rear axle so it hangs down.

Second take the 21mm bolt out of the bar on the drivers side that runs across the rear of the diff. THat will give you the room to get the cover off.


Customer: replied 6 years ago.

DO I just take the 21mm bolt out and let the bar hang down?

YEs or pry it up.


Customer: replied 6 years ago.
Where's the filler plug for the rear differential? Is it a screw type, like the others?

The filler plug is on the passengers side of the diff and takes a square drive ratchet. A 3/8 to be specific.

Just clean the dirt out of the hole first.


Customer: replied 6 years ago.

Thanks, XXXXX XXXXX need to put any sealer on the paper gasket or should I install it dry?


Install it dry, just make sure both the diff and the cover are clean metal.


GM Tech (Cam), GMC Mechanic
Category: GM
Satisfied Customers: 29355
Experience: GM Grand Master Technician 2007. 14 years experience.
GM Tech (Cam) and 4 other GM Specialists are ready to help you
Customer: replied 6 years ago.

Thanksf or all your help. It went well. Getting the residual gasket off the differential was a challenge, but I think I cleaned off the metal pieces well.


The rear differential was definitely messy.



Thanks again.

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