Changing fluid in Rear Differential

I will do my best to explain this hopefully someone will understand.

I have a 1997 Cheverolet, Silverado CK2500, 4x4. We were changing the rear brakes and my husband said the fluid in the rear differential was bad and neaded changed. Ok, I went to the parts store and they gave me 2 jugs of oil, 80/90wt.

The fellows at the part store told me that my truck has a ton'er rear end under it(redoing brakes cost a lot). We were reading in the owners manual and are totally confused. IT looks like there could be 2 different types of rearends under it and don't know how to figure out which one is in the truck. Is there any way to tell? There are 14 bolts(in case that helps). Both rearends require different types of fluid, don't want to mess that up.

Any insite would be helpfull.

I wouldn't fix it unless leaky gaskets or seals.
He can check the fluid with his finger.

He told me it looked "dirty and used". I want to use the truck this weekend and asked if it would hurt anything, he wasn't happy, but said he would check the fluid levels and add any if he needed to, I guess it looses a little when he was changing the brakes?

I don't believe its leaking.

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Both take GL5/80W-90W gear grease.
If limited slip add the additive for it with the new oil.

so you have the 14 bolt locking diff . this in the glove box sticker label should indicate G80 this is the dff. code for the locking differential.

on the diff fill area should be a tag which gives you the oil required. should be 75-90 wt synthetic oil.

when replacing this fluid / gear oil remove the rear cover and clean the metal sludge out. also the cover magnet needs to be cleaned . use paint thinner mineral spirits to clean this .

use form a gasket with a thin paper gasket place on cover let dry for 45 min then install. fill to 1/2 inch below the fill hole.

make sure the venting tube to diff is not restricted.

oil should be brown in color if gray its in need of replacing/cleaning out.

Boy am I glad you guys showed up! Thanks for the info, I am going to print it off and give to him in the morning. Thanks Guys!!

Oh gosh, I just looked up limited slip, I'm totally confused. Can someone exlpain it in laim-ems terms? How do I know if it has limited slip?

You know its terrible, I can drive the truck, pull a trailer and get it in and out of some sticky tight situations, but I have no idea how they work. I even have a "gas ferry".

But, I did get into the brake with my husband yesterday and I cleaned all the little parts and springs. Thats a big thing for me!

Oh gosh, I just looked up limited slip, I'm totally confused. Can someone exlpain it in laim-ems terms? How do I know if it has limited slip?

You know its terrible, I can drive the truck, pull a trailer and get it in and out of some sticky tight situations, but I have no idea how they work. I even have a "gas ferry".

But, I did get into the brake with my husband yesterday and I cleaned all the little parts and springs. Thats a big thing for me!

you have a 2500 4X4 truck . this type of heavy duty vehicle requires the locking differential, or it is possible you have an open differential which does not engage both rear wheels for traction.

both differentials require the use of this synthetic oil because of the high loading on the gears.

limited slip is used in light duty vehicles like cars. this type of diff in a truck would not last very long. this is why the locking differentials are used with our trucks.

the glove box sticker has the coding to inform you of what your vehicle has for equipment. G80 is locking diff..............

the dealership can give you details of this by giving them the VIN number if neccessary.

Thanks iCat, the info was helpful. I stuck my finger in the fluid and it was brown. It didn't look dirty at all as he had said, he is color blind though, that could be the problem. We didn't change the fluids, thankfully, no nead to. THanks

Being a 4X4, the front hud should be checked, and also the transfer case.

If the carrier has weights and springs it is a locker:

http://www.wwdsltd.com/files/373Carrier3.jpg

You can also take a dab of it and let it soak into a business card or other heavy paper stock (this can take some time with higher viscosity oils). New oil would be clean, with a tan color. It will look opaque as it gets dirtier...the spot would look gray and spread out. If the grime is concentrated in the center then the oil dispersants have been depleted and past its life.

Wow, that quite a picture, its a good thing I never strived to be a mechanic!