How To - Drain And Re-fill Your Rear Axle

[Fireman31]

Since Mr. P. did such a great write up for the AWD drive guys with the 10-bolt rear, I figured i'd follow in his foot steps with a how-to for the RWD guys. The pics were taken with a camera phone since my digital camera batteries were dead, and no there aren't any hand shots, those are Steve's trademark.

 

The tools/materials you will need are the following:

-drop light

-scissors or utility knife

-drain pan

-(3) quarts of Mobil 1 75W-90 Synthetic Gear Oil(with GL-5 rating)

-a 3/8 drive ratchet w/3" or 6" extension

-WD-40

-jack handle/tire iron from under rear seat

-shop towels

-a creeper(optional)

 

 

*PLEASE NOTE - it is necessary to remove the spare tire in order to re-fill the differential. Doing so prior to beginning work will make the job much easier. Your truck must also be parked on a level surface.

 

Step 1 -

Lower and remove the spare tire using your tire iron and jack handle.

 

 

Step 2 -

Remove the fill plug from the rear differential cover using a 3/8 drive ratchet and extension of your choice. If the plug is stubborn and difficult to break free, a quick shot with some WD-40 should help break it free.

 

 

Step 3 -

Remove the drain plug from the bottom of the differential using the 3/8 ratchet and extension. Drain the old gear oil into the drain pan. Just beware that the old oil may have a foul odor to it and may also drain slowly depending on how old it is and how many miles are on it. Make sure to inspect the drain plug for metal filings, a heavy filing content means that there is some considerable wear on the differential. After all the gear oil has drained out, clean and re-install the drain plug.

 

 

Step 4-

Begin re-filling the differential with Mobil 1 75W-90 Synthetic Gear Oil. There is no need for any limited slip additives, GM recommends against using any additives in the G80 locking differential. Besides, the Mobil 1 Gear Oil already has friction modifiers mixed in. When cutting the tip of the bottle, cut at the first line. This gives you maximum control of the bottle since the fill hole is in an odd place. Fill the differential until oil starts to weep out of the fill hole, the GM 14-bolt rear end should take all 3 quarts. Carefully clean the fill plug......BE CAREFUL! There is anti-seize compound on the bottom of the fill plug, probably for bearings or such, do not wipe it off! Re-install the fill plug.

 

 

Step 5 -

Test drive, as stated by Mr. P. :

After collecting your tools take your SS to a convenient parking lot and drive in lock-to-lock figure-8s at a comfortable clip (not insane), ten laps ought to do; the figure-8s are good for getting the clutch packs saturated in gear lube, remove varnish build-up from the clutch faces, and sling oil out to the wheel bearings. Finally, after a 15-minute rest check for leaks and lowered fluid level (it may have dropped as much as 1/4-qt, or maybe not).

The proper fluid level for the 14-bolt rear is between 1/2 inch below the fill hole, right up to the fill hole. Anything lower than 1/2 inch from the fill hole should be topped off. As stated, 3 quarts should be enough to re-fill the differential.

 

 

This entire procedure should take somewhere between 1/2 to 1 hour to complete.

Edited September 1, 2008 by Fireman31 (see edit history)

[12'SROCK]

cool write up dan

[Hankg42]

Good job, Dan. I wish I had a drain plug on the rear diff...

[kelleyperformance]

nice how to dan did it fix your issue?

Good job, Dan. I wish I had a drain plug on the rear diff...

you can always get a new girdle... i know the TA has a plug on the bottom. GMPP has a real nice one for the 10 bolt guys

[Fireman31]

nice how to dan did it fix your issue?

 

So far so good, I tested her a bit yesterday....she powerslides around corners much easier now.

[kelleyperformance]

thats always a good thing

[Badkarma]

good write up

[dirtfarmer]

i tryed a 3/8 drive to check oil-- all i do is twist the 3/8 d rive and drain plug is still tight

[Fireman31]

i tryed a 3/8 drive to check oil-- all i do is twist the 3/8 d rive and drain plug is still tight

 

you have to push in on it a bit to get it seated in the fill plug, it will take a 'lil elbow grease to break the plug loose

Edited October 2, 2008 by Fireman31 (see edit history)

[wishminewasanss]

Good write up, but I have one quick ?. It might be dumb but, will this work on a non-14 bolt rear end? Same type of oil grade for a non 14 bolt rear? Thanks!

[misterp]

Good write up, but I have one quick ?. It might be dumb but, will this work on a non-14 bolt rear end? Same type of oil grade for a non 14 bolt rear? Thanks!

The procedure is the same, the fluid you use might differ - in some applications heavy-duty (thick) axle lube might be called for, and in older limited slip differentials you might have to add a tube of "limited slip friction additive".

 

Mr. P.