50k service

debo4x4 · November 19, 2003

I am going to change front/rear dif fluid, transfer case fluid, replace break pads and flush break system myself. Decided I will take it in for trans flush though. I need part #'s and quanties so i can order this stuff online. I checked the plugs and wires and they were fine so I'm going to wait while on those. Can someone help me out?

gm part #

#12378508 for transfer case-- how much?

#1052271 front diff fluid --how much?

#12378261 rear diff fluid--how much?

???? break pad#'s

use standard break fluid or the gm stuff?

I do have the autotrac so I hope this new blue fluid will take care of my "normal" clunk.

Thanks in advance!!

JayMan · November 20, 2003

According to page 0-38 of my Helm shop manual:

AutoTrac: 2.3 quarts, so you need 3

Front axle: 1.75 quarts

Rear Axle: 2.1 quarts, but it WILL hold 2.7 quarts.

Get 5 quarts of gear oil.

For some reason, GM does NOT want you to fill the rear axle all the way up to the bottom of the fill plug. Not sure why. I've always filled mine until it seeps out.

If you've never serviced the transfer case before, make sure to change it again about a week later. MountineerTom has an EXCELLENT guide for this under Important Topics! This is a MUST READ!

The front axle needs regular GL-5 80W-90 gear oil. The rear axle with G80 GovLok needs that expensive GM stuff. Don't use a commercial synthetic 75W-90 or the GovLok will stop working (I speak from experience!).

I now use Mobil 1 75W-90 in both axles. The GovLok seems to work fine. I pay $5.25/quart.

Some more head's up:

Remove the front skid plate before servicing the front axle. This makes the job MUCH easier! Unless you don't mind gear oil oozing off your skid plate Yuck what a mess!

Like MountineerTom said, easy with the transfer case drain/fill bolts. REALLY easy to bugger up the threads or crack the magnesium case. I use a dab of Harvey's Pipe Thread Compound (Thick goopy stuff in a small can) on the bolts. That stuff is good around the house for plumbing and for the truck.

If you don't want to use an expensive synthetic gear oil in the front axle, use something cheap like NAPA 80W-90. Make sure you check the magnet on the drain plug though. The front axle is aluminum and the oil tends to turn to gunk. You may have to drain/fill, drive a week, drain/fill a few times to get all the crap out.

I changed all my fluids at 1600km / 1000 miles and it took 4 times to flush out the front axle. Has been ok since with Mobil 1 Gear Oil.

Good Luck! All the fun in owning a truck is getting dirty, oily, and scraping your knuckles!

ness5575 · November 20, 2003

i just did my front and rear diff's last week, and can pretty much second what jayman said.

why do you want to do the brake pads? mine rear pads lasted till 82k and the fronts still look good at 88k.

debo4x4 · November 20, 2003

The breaks have just gome soft, might not have to replace the pads....we'll see when i got the wheels off. Thanks for all the other tips, i'll keep ya'll informed how everything goes.

seadoons · November 20, 2003

What is govlock? When I changed my rear diff. fluid at 30k I didn't change it again a week later, should I have though? I am planning on changing it again at 60k.

JayMan · November 21, 2003

Order code G80 is the "locking" differential, which is an Eaton Automotive design. Like a limited slip, there are clutch plates inside the carrier.

Instead of using a preload spring to compress the plates, the GovLok uses a governor assembly with flyweights attached to it. When one wheel spins and the other is on firm ground, this causes the flyweights to push out and engage a pawl, which forces the clutch plates together. The axle is now "locked" and you have better traction. GM muscle cars and HD trucks in the late 60's first had this feature.

Advantages are many: You don't have as much drag and friction when the locking isn't needed, and it tends to lock up much better when traction is poor. Though not anywhere near as good as a "real" locking differential.

Most limited slip differentials are torque-sensitive and only transfer 10-30% of available torque to the wheel sitting on bare pavement. A hot rod doing a smoky burnout can force an almost equal transfer, but who drives like that? Not me!

The clutch plates used to be organic, but Eaton Automotive has had much better durability with Carbon Fiber material. The Eaton URL has a lot of information, they used to have a neat video showing how the parts fit together and how they work:

http://www.traction.eaton.com

I think a Detroit Locker is still the best, but every time you turn a sharp corner you have to put up with CLANK CLANK CLANK and that would drive me bonkers!

I was refering to the front axle fluid change possibly needing to flush a few times. The rear axle is iron and the front axle is aluminum. Unless you're having problems with your GovLok I don't think you would ever have to flush the rear axle.

I used to have a 1990 Toyota 4Runner and it had a similar aluminum front axle. The fluid also turned gunky and needed flushing.

If you've never changed your front axle gear oil, be prepared for some nasty stuff when you take off the drain plug. The magnet on the drain plug will probably be covered with black sludge and tiny filings.

Note: never, EVER put solvent or gasoline into a differential to "flush" it! The solvent will get all foamy and you'll have major problems with gear scoring and wiped bearings.

Just use the cheapest gear oil you can find: drain and refill, drive it 20-50 miles to stir things up, drain and refill, drive 20-50 miles to stir things up, etc etc.