Front and Rear Differential fluid R&R

[Dragracer]

I searched the archives on friday and found very little on this, as far as capacitys, some misinformation, and some differences from what was posted. My truck is a 2002 Z71 1500 4X4. I did both axles yesterday and here are some numbers and info. The front takes almost 3 qts of SAE non-synthetic 80W90. You need to pop off the front skidplate of a Z71 truck to allow the fluid to drain. 4 bolts. You could do it without removing the plate, but it could make a big mess. The fill/drain plugs are accesible with the skidplate in place. The lower drain plug is magnetic on the front diff. The rear differential takes just shy of 3 qts of SAE Synthetic 75W90. One thing that I was surprised to see(after I had purchased a cover gasket already) was that there is actually a drain plug on the very bottom of the differential. It is the same type of square head as the fill plug that you simply use a 3/8" drive extension directly to remove. The drain plug is a taped seat countersunk into the housing flush. I was prepared from reading the archives to remove the differential cover to drain the fluid. Not necessary in this case with a drain plug provided. GM does not recommend changing the fluids at any point up to 150K as specified in the maintenance, but I would recommend if anyone's truck is at or approaching 100K to do it anyway. My fluids were pretty black when drained at 140K. I also felt that since GM doesn't require the fluids to be changed, the OEM fluid must be pretty good, so rather than buy a decent Amalie/Kendall or Mobil 1 to put back in, I would rather spend the extra bucks and buy the fluid directly from GM. The rear sythetic is about $20/qt and the front is cheaper at around $5/qt. The gasket was $5 but I didn't use or need it as mentioned. The GM p/n's are in the owners manual for the fluids. Hope this info helps someone out when the time comes to do it.

[isjustus]

I think in 03? they lost the rear diff drain plug.

[Z66 BUTCH]

The rear differential takes just shy of 3 qts of SAE Synthetic 75W90.  GM does not recommend changing the fluids at any point up to 150K as specified in the maintenance, but I would recommend if anyone's truck is at or approaching 100K to do it anyway. My fluids were pretty black when drained at 140K. I also felt that since GM doesn't require the fluids to be changed, the OEM fluid must be pretty good, so rather than buy a decent Amalie/Kendall or Mobil 1 to put back in, I would rather spend the extra bucks and buy the fluid directly from GM. The rear sythetic is about $20/qt and the front is cheaper at around $5/qt. The gasket was $5 but I didn't use or need it as mentioned. The GM p/n's are in the owners manual for the fluids. Hope this info helps someone out when the time comes to do it.

So is GM using SAE Synthetic 75W90 in the rear diff from the factory? I have a Z66 with the locker.

Butch

[cadboy1]

I think in 03? they lost the rear diff drain plug.

My 03 does NOT have one

[rcornwell1]

I'd like to add to dragracer's comments.  I bought all three fluids from the dealer front/rear axel plus transaxle fluids at $63.38.  That was 3 bottles each.  I had a little left over of each.  There would have been more of the transaxle fluid but I left quite a bit on me and the floor.  Invest in one of those hand pumps from Harbor freight 5-10 bucks is worth it.  I only have 40,000 on an 02' Z71 and I think $63.00 is cheap insurance.  One other item you may need.  The rear fluid is to be
5/8 to 1 5/8 inches below the fill plug.   Just bend a coat hanger a little over 1 5/8 and cut to length 1 5/8.  Notch down from the bend 5/8" now you have a dipstick to measure the rear axle fluid.


Cheers
Bob

[loneraider]

From what i have seen here   (in posts)  the rear diff plug was stopped in production in May 2002 or shortly there after....
also the transmission pan drain plug was deleted in 2003 ( can antone verify this?)