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Front and Rear Differential fluid R&R

Dragracer

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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.
 

pktwatch

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Dragracer said:
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
 

rcornwell1

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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

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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?)
 

SpottyJ

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Dragracer said:
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.


Question for anyone who has changed their front differential fluid - how much fluid did you use? 


I changed the fluid on my 2003 and it only took about a quart and three quarters.  The fluid was running out of the fill hole (both when front was raised and on level ground).
 

mleeber

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Well, I just changed my Diffs and transfer case, or started to.... Dealer said the containers of fluid were "single serving" and that I only needed one each. Clearly that was not right but now I find out that I got the last quart of Dino oil for the front diff, GM has discontinued it and is now subbing the synthetic PN for the rear to be used in the front as well. I have 200K on the AV and I am not going to risk seal issues so I guess it is off to the auto parts store for some 80W90.
 

Bear63

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GOOD INFO here!  Thanks!  (y)
I recently (last week) acquired a 2002 Z66 with approx 197K miles on the clock.  :B:
It seems to have been pretty well maintained (clean/clear fluids, newer hoses & belts, runs great, no vibrations, no issues, everything works  :D ), but I'll likely drain/refill the rear diff fluid anyway as I KNOW that this is an often missed maintenance item.
I also noticed that the rear diff appears to have a slow leak around either the drain plug OR the bottom of the rear cover (doesn't appear to be the pinion seal as that area is dry, but I'll need to crawl underneath & take a closer look to be 100% certain).
Q:  Has anyone used the Permatex or Loctite Thread sealant on this rear diff drain plug to prevent weeping?
Q:  What other high-quality synthetic rear-axle oils have other owners been using?  (...besides just handing over the $$ for the GM factory stuff.)
...
Also:  For those of you with 4WD systems (& a front diff), I'd recommend checking with NAPA Auto Parts for the old-school "dinosaur oil" gear oils that you require.
 

Bear63

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Has anyone used the Mobil 1 Synthetic 75W90 Gear Oil in their rear differential?  Any issues??

My local Napa sells it for $12.99/quart.  Seems like it would be a good, quality choice, at a reasonable price point.

(Napa ALSO HAS Valvoline Synpower 75W90 Gear Oil for $12.99/quart, OR Castrol Syntrax Limited Slip 75W90 Gear Oil for $14.99/quart, OR Royal Purple Max-Gear 75W90 Gear Oil for $22.49/quart, OR Sta-Lube SYN-GO Synthetic for $19.99/quart.)
 

EXT4ME

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I use Mobil 1 Synthetic 75W90 Gear Oil in the front and the rear differential.
 

Shylok's

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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.
Hi I see this is a pretty old tread but hoping you answer. So I need to do new axle and I'm gonna do it myself since the mechanic put a wrong one on and now everything is ffd up. I didn't know that you had to drain fluid from the differential to change the axle, is that what you did? Asking cuz I'm trying to watch videos and read up before I do the job I just can't trust any mechanics here. Two different guys have pretty much destroyed my beautiful truck by not doing stuff right and swapping and stealing my parts off my truck. Anyways like I was saying the videos I've watched they just take the axle off and with no oil spillage or mention that they drained it first. I'm glad I saw this first or I would've made a huge mess. So just to make sure cuz I have the same truck you do or did.
 

ygmn

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if replacing the entire rear axle assembly yes you do not have to drain since you do not need to open it up.
Front is a bit different since it is not a solid axle.
 
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