Rear axle oil change

stef8 · April 22, 2004

I have a 99 Silverado 4.8 with a 3.42 rear axle and I want to change the oil in the rear diff. According to the Helm shop manual, I need to know the size of the ring gear, 8 1/2, 9 1/2 or 10 1/2 inch. cause they all have different oil capacities.

Is there a way to know which ring gear I have?

Thanks

Stef

frdfandc · April 22, 2004

You fill the rear till the fluid starts to come out of the fill hole.

Nick99Chevy · April 22, 2004

1/2 Ton truck should be 9.625" rear

REDZ-71 · April 22, 2004

If you have ten bolts on the rear axle cover, then it is a 8.5" ring-gear axle.

Most 1500 series trucks are 8.5" ring-gear axles

citydriver · April 22, 2004

You fill the rear till the fluid starts to come out of the fill hole.

this is the best way to get the correct fluid level

But knowing which axle you have is a bonus if you r going to use a diff. cover gasket...makes it easier to buy the right one

April 22, 2004

I have a 2003 Silverado that came with the 3.42 rear differential. I changed the 3.42 for 4.10's and the gears and limited slip I bought were for the 8.5" housing. Unless things changed between 1999 and 2003, I would have to believe yours is an 8.5" also.

As to filling the rear differential with fluid, it is my understanding that it is to be filled until you can stick your finger into the fill hole, bend the finger at the first joint and you should be able to touch the top of the fluid with your finger. Some use the short bent part of an allen wrench rather than their finger for this test. I've never actually filled the rear differential, so maybe an expert can jump in here and say for sure how it should be done. I could be wrong!

asepgrad98 · April 22, 2004

You are not supposed to fill the new body style trucks up to the fill hole. I believe it is 5/8" below.

stef8 · April 22, 2004

Thanks to all of you for the infos. The owners manual state that the 1500 series rear axle should be between 5/8 and 1 5/8 inch below the filler plug but that doesn't tell how much oil I'll have to buy ( plus the additive for the clutch) . I looked in the shop manual and it says:

8 1/2 inch ring gear : 2.1 quarts

9 1/2 inch ring gear : 2.7 quarts

10 1/2 inch ring gear : 3.25 quarts

I guess I'll buy 3 quarts and put the additive first and then the oil until it reach the maximum level of 5/8 inch below the plug.

Thanks again!

Stef

fastdrvr23 · April 22, 2004

Thanks to all of you for the infos. The owners manual state that the 1500 series rear axle should be between 5/8 and 1 5/8 inch below the filler plug but that doesn't tell how much oil I'll have to buy ( plus the additive for the clutch) . I looked in the shop manual and it says:

8 1/2 inch ring gear : 2.1 quarts

9 1/2 inch ring gear : 2.7 quarts

10 1/2 inch ring gear : 3.25 quarts

I guess I'll buy 3 quarts and put the additive first and then the oil until it reach the maximum level of 5/8 inch below the plug.

Thanks again!

Stef

Your specs. should be right on, My 03' has a 10 Bolt, 8.625" (I guess they round to 8.5), 30 Spline Open Carrier. I had to check when I was going to order a locker. Even if yours is a LSD unit, the dimensions should be the same.

I guessing you must have the LSD rear and not the open since you are going to use the additive? (I've forgotten to add that stuff in my old truck probably 2 or three times since it was an LSD, and I bought it for my new truck with an open carrier. lol)

I have the same setup with an open diff... It took me just a hair over 2 quarts (just like you posted) of mobil 1 for mine. I used an allen wrench marked at 1 inch depth (I figured it was a good compromise for the level in the owner's manual) to check the level.

The guy at the GM parts counter told me I didn't need any RTV or anything on the new gasket, so I didn't use any. It seems to be doing fine after about 4,000 miles so far. Good luck with it!

Will

Greek · April 22, 2004

I've replaced mine three times so far. First time I also replaced the gasket. I used the little finger method the first time. Second time I used the allen wrench, much better method. The stuff goes in real slow so you have to be patient. I used Mobil 1 the first time then the GM Synthetic(2000 -1500 Z71 Silverado, with a 5.3 engine, 54K miles).

ness5575 · April 22, 2004

I guess I'll buy 3 quarts and put the additive first and then the oil until it reach the maximum level of 5/8 inch below the plug.

i thought that no additive was required for the nbs trucks?

tmf6902 · April 22, 2004

This has nothing to do with the topic...well sort of...anyway I was watching a off roading tv show..and they showed this trick if your off road and need to take the diff cover off...losing your fluid and have no funnel to get it back in there....stick it(the oil) in a zip-loc bag...but the bag in the diff.....bolt it up, and turn the wheels by hand....the diff will bust the bag...and bam..you have a filled diff...they said the bag gets ground up harmlessly.....so they say

silverado19 · April 22, 2004

I just did my rear. (10 bolt) Removed the cover, cleaned the magnet, removed the old gasket....got as much of the old gasket off the cover and housing I could, installed a new gasket and bolted it back up. I used the allen wrench method to measure the 5/8" to 1 and 5/8" of RedLine 75W90 oil I put in. I used a bit over 2 QTs. No leaks and all seems well.

There is also a guide on how to change the fluid. Just click on the guides link on the home page for this site and find the guide that says...Change the Rear Diff. Oil!

Good luck.

silverado19 · April 22, 2004

I forgot to mention in my prior post....It is a good idea to remove the filler plug bolt first. This is so you can be sure you can add the new oil to your rear end.

Nothing is worse than getting the drain plug off, draining the old oil, taking the cover off, cleaning everything off, installing the new gasket and cover.....AND YOU CAN'T PUT ANY OIL IN THE REAR END!!!! @#$%%^$#@!!!!!

If your filler plug is frozen, deal with this issue first and the rest will be a breeze!!

stef8 · April 23, 2004

I noticed that some of you are talking about removing the cover and replacing the gasket. Why is this necessary, isn't the magnet located on the drain plug? Unless a lot of dirt is sticking to the cover and needs to be cleaned properly?

Stef