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Discussion Starter #1
I want to drain and change the lube in my 1998 Suburban 1/2 ton 2wd.Imagine my surprise when I looked at the diff and can't find a drain plug.I found the plug to add fluid, but nothing to drain it.
The manual also don't say anything about routine maintenance-draining and changing the lube.It does mention topping it up, but nothing about draining.
I've had it about 1 year, put about 8000 of the 202,500 miles on it. It runs great, and I want it to continue that way! It also get 21 mpg at 70 mph, so I really want to keep it! Typical 12-14 mpg city-3.42 diff..

Is this supposed to be last forever lube- a no maintenance-other than topping it- rear differential.

I'm considering sucking it out with a 60cc syringe and a bit of tubing.I don't know that something that thick would siphon out.

Any ideas?
Thanks,
Charlie
 

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It's pretty easy, but very messy. You have to pull the rear diff cover. Make sure you go and get a gasket for the diff cover. You should have a 10-bolt under there. Lossen all the bolts on the diff cover, top first, then bottom. All the fluid's gonna come out between the diff cover and the diff. Clean everything out pretty well, scrape off any old gasket material, and bolt the cover back up with the new gasket. Fill 'er up and drop some of the poistraction diff fluid modifier in there for good measure. You're done...
 

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You can also get a fill kit with a hand pump so you don't have to try and get the little tip of the bottle in the hole in the top of your diff. Tkink there pretty cheep too.
 

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I'm lazy, and I dont like the mess of all the diff fluid draining into a drip pan I've then gotta clean up. So a few years ago while laying under my truck stalling and delaying the inevitable chore of pulling off the rear cover I came upon the idea of using the syphon pump I bought to change the oil in my boat.
After removing the fill plug I stick the pump suction hose in the fill plug hole, stick the pump exhaust tube in an empty gallon jug and give'er a few pumps, only takes about 5 pulls to remove all the lube from the diff. Cap the jug, remove the suction hose and refill the diff.
 

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Discussion Starter #5
Crawdaddy,Crane3447, tbplus10,
Thanks for the info guys. No drain plug. I also hate the mess, and diff lube is the smelliest stuff so if/when I get it on my work clothes, it will take forever to come out. My wife won't be too happy about me throwing than in the washer.

I think I'll get one of those siphon sucker outters and something to pump it back in also. If I take the cover off with my luck I'll screw up the reinstall and develope a slow leak.

I'll try the expensive syn lube.I kinda doubt I'll measure better mpg, but I'm curious.
Thanks,
Charlie
 

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if you have not done this chore. before you do it, go buy yourself one of those cool looking cover with a drain on it. so next time all you have to do is drain and re-fill.
 

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Discussion Starter #7
I took TBPLUS10's advice,and siphoned it out. I got out about 2.25 quarts- it took about 40 minutes for the flow to stop since the lube is sooo thick. I refilled with Mobil I 75W90 syn lube.It was lots of fun turning the refill bottles upside down and getting them to drain in. I finally reached around and stabbed the bottom with a pocket knife to get it to drain faster - not a lot of room, exhaust and some lines in the way. Now I'm ready for another 3000 mile trip next month.

esponet-Yes, it would be cool to have a nice finned aluminum cover with a drain plug- next time.

Thanks guys,
Charlie
 

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When you decide to buy a new cover spend a little time researching them. The cheaper stamped steel covers have been known to warp and cause leakage, they dont always seal properly even with the correct gasket material.
 

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I pulled my cover, it all went in drain bucket, scrapped off the old material, ran a 1/4" bead of black Permatex around the housing, screwed the bolts back in and laid the Mobil 1 75-90 to it. I also wiped out excess inside, found not metal grindings. I hit the outside of the cover with a wire brush and got off a bunch of rust (been run in PA during winters) painted the cover with moly lube which is a excellent corrosion fighter.
I will probably put in some moly powder at some point when I feel energetic.
No leaks
 

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Discussion Starter #10
I don't know if the 75w90 Mobil 1 syn helped my mpg but it sure didn't hurt.Got 21.2 mpg on our last trip to Arizona 3 weeks ago(3085 miles). Two months earlier the same trip got 21.3 mpg -BUT this trip it was hotter than Hades the whole trip ,and the AC- both ft and back- ran on the highest setting the whole time.

It was over 100 degrees from 200 miles East of Dallas Fort Worth to 100 miles NW.DWF was a LOT HOTTER THAN New Orleans!! The trip before - early May-it was cool averaging maybe 65 degrees and it snowed in Flagstaff.

I don't know how much full AC-front and back- hurts FE but it is probably much more than .1mpg.The Suburban has a huge interior- lot of volume to cool. Oh,I am sure glad it is white-much cooler than the little black Prius we have-that sucker is an oven all summer. Never buy a black car if you live in the south.

Charlie
 

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Do any of you who are running Mobil1 synthetic in their rear difs have the Limitied Slip (G80) differential?

This is what I have and my manual calls for synthetic fluid plus I'm told that you are supposed to add the LS additive to the G80 differentials. However, the Mobil1 lable says that it is forumlated with the LS friction modifiers. But if you go to the Mobil1 website, it says you can still add manufacturer-specific LS additives to the Mobil1 fluid.

I think I may first try it without the additives and see how it goes but I thought I would see if anyone has had any experience doing it one way or the other.

Also, I've seen some conflicting info on the bolt torque for the cover bolts. I have something printed from the service manual that says only 13 ft-lb but I think I've seen 28-29 ft-lb elsewhere.
 

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A little extra friction modifier never hurt, but not enough definitely will. My uncle and I actually put the LS friction modifier in our non-LS rearends to make sure they stay nice and quiet. I'm still running good-ol' dino gear oil.
 

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A little extra friction modifier never hurt, but not enough definitely will. My uncle and I actually put the LS friction modifier in our non-LS rearends to make sure they stay nice and quiet. I'm still running good-ol' dino gear oil.
I just came across this discussion on the use of Mobil1 and LS modifiers for the G80.

To summarize, if you use Mobil1 then the modifiers are not needed. Also says you can run dino oil with more frequent fluid changes than the synthetic.

On another subject (that I'll probably post on its own thread), what is eveyone using in their tranny? You can't find just Dexron-III in most parts stores anymore, just Dexron-VI which works but is still pretty expensive because it is synthetic. If I want to do a full fluid change it will be 14 quarts of the stuff.

I'm leary about the multi-purpose Dex/Merc fluids and I'd rather pony up for the DexVI than go with one of the multi-purpose fluids (even though they say they are Dex-III compatible). I know from having a Chrysler that you can easily kill a tranny by using the wrong fluids even if you use the additives that are supposed to make them compatible.

I may still be able to get true DexIII from the dealer but I'll have to check on that.
 

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You have to remove the differential cover. If you are going to use a gasket, make sure that you clean off the surface of both the differentail cover and the differentail housing. You can use brake clean to clean off the surfaces. While you are there you might want to wipe out the bottom of the differential case but, make sure that you don't spray the differentail carrier bearings or ring gear and pinion bearings.

If you are using a Anerobic Silicone Gasket (not the Silicone for caulking bathtubs and around the house usage) make sure you use a quality automotive anerobic gasket silicone!!! Follow the directions on the package. If you don't it will leak!!!

Torque the bolts to 13-18 ft. lbs and fill with the recomended gear oil.

If you have a limited slip differential don't forget to put in the limited slip friction modifier or you will burn out the clutch packs in the diferential clutch packs! Make sure you follow the directions on the bottle or the manufacturers directions.

Top off gear oil to the bottom of the fill plug, but do not overfill past that.
Afterwards, I usually tilt the vehicle side to side on a slight incline of a hill to make sure the gear oil flows to the outer left and right wheel bearings.

Hope this helped for all of the DIY out there!
 

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It might be worthwhile to add a drain plug to the bottom of the cover. They make the drain plug bungs that you drill the hole and bolt or weld it in. You could add a temperature sender while you were at it too... ;)
 

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It might be worthwhile to add a drain plug to the bottom of the cover. They make the drain plug bungs that you drill the hole and bolt or weld it in. You could add a temperature sender while you were at it too... ;)
I just did a fluid change on my 2002 with the G80 and it has its own drain plug (not on the cover). Since this was the first time I changed the fluid, I went ahead and removed the cover so I could see what kind of debris was stuck to the magnet. It was all very fine stuff, no shavings whatsoever and the gears looked good.

Of course the tough part of this job is cleaning the old paper gasket material off of the cover and its mating surface. I used about 2.5 qt of Mobil 1 75W90 LS to fill it back up. Also used some Permatex high-tack gasket adhesive on a new Fel-Pro paper gasket. All told it is about a 1 hour job but next time, I might just drain it from the plug and fill it. That could be done in about 10 minutes.
 

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The pump is the way to go. Take your time and try to get all the fluid at the bottom. It is not the same detail as pulling the cover, but unless you have problems with the gears, this will do the trick in about 5 minutes.
 
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