AFAIK GM put the front axle to the same synthetic 75W-90 "grape juice" as used in the rear axle. I used to have a 2000 GMC Sierra 4x4 and the dealership told me about a tsb dated Feb of 2003 regarding use of synthetic oil in the front axle.
Any way I can attach pdf's to this forum? At one time, anybody could access the GM TechLine website and download bulletins, now you require password access. I do have the bulletin in question if anybody is interested:
"IMPORTANT: This information is
intended for vehicles sold in very cold
weather climates, especially those in
Alaska and certain regions of Canada.
An upcoming bulletin addresses the
use of synthetic front axle lubricant for
4wd C/K trucks with 9.25-inch front axle
assemblies sold in cold weather climates.
TIP: Provide a copy of the bulletin to
the owner when the lubricant is replaced.
The mineral based fluid
used in the front axles of
these vehicles may not
lubricate properly at -12°F
(-24°C) or below. This may
contribute to premature
pinion bearing wear if a
vehicle is driven extensively
in very low ambient temperatures.
Before delivery to the
first retail customer, the
front axle fluid should be
drained and refilled with
synthetic axle lubricant, following
the service manual
procedure (document
673354)."
When my 2000 GMC had around 1,000 km on it, I drained and refilled the front axle to Exxon Synthetic 75W-90. I changed the front axle yearly with a heavy duty 75W-90 lube.
Kind of cute how at first my dealership told me I was "wasting money" by putting a synthetic in the front axle, then with a red face he handed me a tsb several years down the road that recommended it.
My truck had the AutoTrak, so only AutoTrak II fluid can be used. It's a distinctive blue color
The rear axle needs the dealership "grape juice" synthetic 75W-90 at around $25 a litre. Supposedly it has the additives needed to keep the clutch plates working in the G80 "locking" rear axle. I've used Mobil 1 Gear Oil 75W-90 with good results, the G80 kept workikng
The 4L60E needs whatever current Dexron spec fluid GM recommends for that year. My 4L60E had a factory drain plug but it was fubar'd from the factory, so I had to use a MityVac to siphon out the fluid, then drop the pan. It's tight clearance between the exhaust crossover and the pan, but you can get it off.
I serviced my 4L60E the same time I did the axles and transfer, at 1,000 km. Then every 12 months
