How do you drain rear differential lube 98 Suburban?

**phoebeisis** · 06-09-2008, 05:50 PM

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

**Crawdaddy** · 06-09-2008, 08:18 PM

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...

**crane3447** · 06-09-2008, 08:45 PM

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.

**tbplus10** · 06-10-2008, 10:54 AM

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.

**phoebeisis** · 06-10-2008, 11:37 AM

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

**esponet** · 06-14-2008, 02:26 AM

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.

**phoebeisis** · 06-15-2008, 10:29 AM

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

**tbplus10** · 06-15-2008, 11:51 AM

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.

**Hummer** · 07-28-2008, 06:02 PM

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

**phoebeisis** · 07-28-2008, 07:09 PM

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