After reading so many debates one way or the other, I decided to do what mechanics for decades have done, fill to the hole. So in either instance, you need two bottles (quarts) to get the job done.

 

I used Castrol Syntrax Longlife 75w-90 for open diffs, and genuine IYK500010 for TC

I bought from autohausaz . com - no tax, free ship if you spend $48+

Castrol diff oil is $19, genuine LR TC fluid is $32

 

I wound up going with the Royal Purple 75/90 for the rear unlocked and synchromax for the transfer case. How crucial is replacing the washers for the fill plugs on the transfer case? Went to check it out this morning and seems like I’m leaking just a little bit from the drain plug on the TC. Wondering if it’s from not replacing the washers. Anyone know?

 

You should replace the washers ideally. Copper works great. If its leaking, then you should have replaced them. But they dont hold pressure, so spark them down with cleaner to be certain there is a leak. If there is, then tighten them up a bit more. TC has an aluminum housing, so dont do it when warm and dont torque too much.

 

Thanks for the awesome information. Rear diff looks to be a clean fluid change, no leaks. There was some noise, not the usual grinding, when I initially put the car in reverse this morning but was gone after I drove it around the block. Is this typical after a fluid change or something I should be worried about?

Also, tightened up the transfer case plug and cleaned it up. Hopefully will solve the drip issue.

Thanks everyone for all your help!

 

There would normally be no noise after a fluid change. Probably something else.

 

I followed this direction:

Front Differential
Oil: Castrol Syntrax Longlife 75w-90 (LRN7591) x1
Royal Purple Max Gear (01300) 75w-90 x1

1. Remove engine skid plate
2. Clean area around drain and fill plugs, remove fill plug
3. Remove drain plug, drain fluid
4. Install drain plug; up to sn 254845, hex plug = 54Nm (40 lb-ft), from sn 254836, 3/8" square plug = 28Nm (21 lb-ft)
5. Fill with 0.61 litres (1.07 pints) (0.64 US quarts) Castrol SAF-XO - 75W/90 (LRN 7591)
6. Tighten filler plug to 34Nm (25 lb-ft)
7. Reinstall engine skid Plate.


Rear Differential (Non-locking)
Oil: Castrol Syntrax Longlife 75w-90 (LRN7591) x2
Royal Purple Max Gear (01300) 75w-90 x2

1. Raise and support vehicle CAUTION: Do not undo or remove the large protruding hexagonal on the differential casing.
2. Clean the area around the differential fill plug and drain plug, remove the fill plug
3. Position container to collect fluid, remove the drain plug. Drain fluid
4. Install drain plug. Up to diff sn 254325, hex plug = 54Nm (40 lb-ft) from diff sn 254326, 3/8" square plug = 28 Nm (21 lb-ft)
5. Refill with correct fluid and quantity;
7. Install filler plug and tighten to 34Nm (25lb-ft)


Transfer Case
Oil: Shell TF 0753 (LRN0753, IYK500010) x2
Royal Purple Synchromax (01512) x2

1. Raise and support vehicle
2. Position a container to collect fluid
3. Clean area around fluid drain plug, remove plug and discard the sealing washer.
4. Allow fluid to drain
5. Clean component mating faces, install a new sealing washer, install drain plug and tighten to 22Nm (16lb-ft)
6. Remove the filler/level plug, clean the immediate are and discard the sealing washer
7. Refill transfer case until the level with the filler hole. (1.5 litres)(2.6 US pints)(1.5 US quarts)
8. Install the fluid filler/level plug with a new sealing washer and tighten to 22Nm (16l lb-ft)

 

just quoting to reiterate, ALWAYS remove the fill plug first. The last thing you want is to drain the oil and find the fill plug wont come out.

 

Thanks for this post of knowledge! Does this mean that GM part # 92184900 is exclusively meant for rear locking diffs?

 

The GM stuff is specific to carbon clutched diffs. But you can use the fluid in non-locking diffs since it won't matter. Not sure about use in other locking diffs that use different material. Would be a waste of money though.