Rear Differential question...

[{tpc}]

Ok to add to the list of things I am working on for my truck, I want to change the rear diff fluid. Its is the g80 with 3.73 gears, for reference.

Seems easy enough, buy gasket, buy 3 quarts of mobil 1 synthetic 75w90, get fill plug loose, pull diff cover, drain, clean, back together with new gasket and fill.

Ok now for the dumb questions. For anyone who has done this, is getting 3 quarts a waste? It seems from the alldata info that its a bit over 2 quarts to fill, hence why I was getting 3. But maybe it is wrong, I dunno.

Second, is there any reason at all to "lift" the vehicle when doing this? I can see maybe moving the spare out to make it easier, but it seems unnecessary to lift it. However in the all data procedures it says lift the vehicle. I'm fairly certain I could shimmy under where all this is with no need to lift anything.

Anything I may be missing?

 

[triz]

On the TB its about the same.I just did it recently, off memory it was about 2.5. Still have the half in the back. If your just changing fluid. make sure your fill plug comes loose first before draining.

Do you have a drain plug as well or do you have to remove your diff cover?

 

[DAlastDON]

I had access to a lift when i did mine when i first purchased the truck. Did not have to remove the spare but i would imagine the quarters being tighter without it lifted.

When putting the bolts back in snug them in a criss cross star pattern like you would lug nuts. Do you already have a pump to get the fluid into the differential?

 

[{tpc}]

I "think" the cover has to be removed. I have the hand pump I used for the front diff so I could use that or buy a clean one. Really gives the forearms a workout! Lol

 

[HARDTRAILZ]

I would remove the cover and take a look and give it a good cleaning while you are doing it. Simple enough not to skimp on.

 

[seanpooh]

There's a magnet on the inside of the cover too which you could wipe off clean. It's beneficial.

 

[{tpc}]

Ok so I am going to work on this today, hopefully. 2 questions. One is about the gasket. The only ones I can find around here are the $5 blue felpro gaskets. Are these good to use? Or should I wait and try to find a gm one to replace it?

Second question is about the gear lube. So originally I thought I was able to find mobile 1 synthetic. But the mobile 1 I found says LS on the bottle, as does most of the gear lubes I find. Actually, most everything states "suitable for limited slip". I was able to find a lucas oil gear lube that doesn't say LS on the bottle. So which to use? I have the G80, and I have heard or read that your not supposed to put any limited slip additives in there, hence my question.

So basically, are felpro blue gaskets for $5 crap? And what 75w90 synthetic gear oil should I put in there? LS on the bottle or definitely not?

Thanks all for the help on everything.

 

[Sparky]

These differential covers have a reusable rubber gasket. I just cleaned mine up before reinstalling.

Not really sure on the G80 thing as mine is open. I just have some plain old Valvoline 75W-90 in mine.

 

[BlazingTrails]

I use gasket maker on mine. G80 just need reg dif fluid.

 

[{tpc}]

Mine doesn't have the reuseable gasket....some paper stuff...looked to be original. I used the felpro one with a thin coating of ultra black. Just waiting a little while before I dump the gear lube back in. Also went with the lucas oil stuff.

Has to be better than the stuff that came out which was fairly dark. No metal though, magnet looked pretty good too.

 

[{tpc}]

Here is another interesting question. How do you know its full? When it comes back out of the hole?

 

[Wooluf1952]

Here is another interesting question. How do you know its full? When it comes back out of the hole?

[SIZE=12.0524063110352px]That's it. IIRC, it only needs to be about a 1/4' below the fill hole, but even with the hole won't hurt.[/SIZE]

 

[{tpc}]

Well all done. Took for a little test drive, sounds normal, maybe better than normal. So far so good, no leaks!

 

[Sparky]

I realize now we're talking about your Tahoe not a GMT360. Sorry, my reusable gasket reference only applied to that platform

 

[Mooseman]

If I don't have a reusable rubber gasket, I just use RTV, no gasket. Been doing this for 30+ years, saved some $.

For reference for the lube, it doesn't matter if it has the limited slip additive or not. It's just a friction modifier for the clutches in LS diffs so they slip better. As long as it's synthetic 75w90, it's good to go in open and G80 diffs. LS has to have the additive unless the bottle says it's included.

 

[{tpc}]

If I don't have a reusable rubber gasket, I just use RTV, no gasket. Been doing this for 30+ years, saved some $.

For reference for the lube, it doesn't matter if it has the limited slip additive or not. It's just a friction modifier for the clutches in LS diffs so they slip better. As long as it's synthetic 75w90, it's good to go in open and G80 diffs. LS has to have the additive unless the bottle says it's included.

That's good information to know, thank
you. Again, I figured I was being overly anal about the subject, so I decided to jump in with both feet lol.

Funny the things I worry about sometimes..

 

[BlazingTrails]

I use gasket maker on mine. G80 just need reg dif fluid.

Sorry I was busy earlier and didn't have time to elaborate. Thanks mooseman

 

[{tpc}]

Sorry I was busy earlier and didn't have time to elaborate. Thanks mooseman

Sorry, I didn't mean anything by my earlier comment. The gasket maker stuff makes sense, I didn't even know I had ultra back (son had it in the garage) before I bought the gasket itself. My comments to mooseman were directed towards the explanation on the fluid. I looked high and low trying to figure that out, and didn't have much luck. Lots of opinions out there, but I trust the people here a lot more than in some other places.

Anyways, hope you didn't take offense, blazing. I do appreciate the help.

 

[BlazingTrails]

No offence taken. I literally didn't have time to elaborate when I posted. I usually like to include some reasoning in my post. Mooseman filled in the gap.

 

[Blackwater]

I know this is possibly after the fact. With a G80 there is a special fluid from GM that needs to be added to it for the limited slip. When I put my Detroit locker in it only recommended Lucas synthetic 75/90W. It was the same for the primary and secondary tranny. I also took the liberty to add two heavy duty magnets from radio shack to the bottom of the pumpkin away from the ring gear.

 

[Wooluf1952]

The G80 is a locker and doesn't need a special fluid. The SS diff.(G86?) is limited-slip and needs a special fluid.