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Front and Rear Differential fluid R&R

Dragracer

Full Member
Joined
Jun 17, 2005
Messages
123
Location
NH
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.
 
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
 
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
 
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?)
 
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).
 
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.
 
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.
 
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.)
 
I use Mobil 1 Synthetic 75W90 Gear Oil in the front and the rear differential.
 
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.
 
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.
 
bringing this back to the top. Went to the dealer to verify the correct fluids and they told me that the front and rear diff get the same fluid....the 75W-90 synthetic GL-5. I saw another post about this earlier in this thread. Can yall confirm that info is correct? I hate to rely on a one persons answer at a dealer. I did go with the AC Delco fluid, but they only had 4 quarts. I got the rear diff cover pulled, and cleaned off the gasket material, but ran out of daylight, so I will resume tomorrow on the rear. Let me know what yall are running in the front these days. Thanks! OH...and I hope I have the right gasket. The part number Oreily looked up and gave me is a Fel Pro RDS 55028-1. Hope its the right one or Im going back to the store again.

While on the subject.....with the gasket, do yall put the rear end permatex RTV onto each side of the gasket (with a light coating) in addition to the Fel pro gasket to keep things in place?
 
Following is the installation procedure as outlined in volume 1 of 4, page 4-161 of the actual 2003 GM Service Manual.

I will try to faithfully type it as it appears.

Installation Procedure
1. Install a new gasket and rear axle housing cover.
Notice: Refer to Fastener Notice on page P-9 in Cautions and Notices.
Important: Do not reuse the rear axle housing cover bolts.
2. Install the new rear axle cover bolts (1).
Tighten
Tighten the bolts to 40 N-m (30 lb ft).
3. Fill the rear axle. Use the proper fluid. Refer to Capacities - Appropriate Fluid on page 0-35 and Fluid and Lubricant Recommendation on page 0-36 in Maintenance and Lubrication.
4. Install the rear axle fill plug.
Tighten
Tighten the rear axle fill plug to 33 N-m (24 lb ft).
5. Lower the vehicle.


As I read it, there is no recommendation of any type of additional sealer to be applied to the rear axle cover gasket, so I am sure you would be correct in not using any.

Second, it is stressed to discard the old bolts and install new ones.

In regards to the torque specs, years ago I had a Suburban that kept developing leaks at the rear axle cover.

Amazingly, I had a couple of different shops attempt to remedy this situation, with limited success each time.

Finally, the last mechanic I chose to look at it discovered the actual cause of the leak.

After very carefully examining the rear axle cover, he found if he placed the cover in a vise and carefully flexed the cover with a pair of pliers at each bolt hole, there were tiny hairline cracks around several of the bolts holes.

When not under flex pressure, the cracks in the cover were not visible.

Once we acquired and installed a new cover with new bolts, gasket and proper installation techniques, the saga of the leaking rear end on that truck was finally concluded.

We surmised that during previous attempts at fixing the leak, copious amounts of sealer and over tightening of the cover bolts did nothing but stop the leaks in the short term and ultimately damaged the cover to the point it needed to be replaced.
 
My 2003 takes just over 1.5 quarts in front diff.
Believe there the same

No rear diff plug, it was worthless anyways just
Like the trans drain plug. Most trans plugs could not loosen.

Front leaks out On most GM front diffs, I use 80w 90 supertech

Mobil 1 or valvoline 75w 90 in rear diff just fine
 
Last edited:
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.
Im having a hell of a time locating OEM part # for all of the fluids. The transmission is in a 2010 and I think I got the OEM fluid #s. But the three holes below , front and rear differential, plus transfer case #s I cant find to order on line. Every time I do a search some other brand oils, lubricants and such pop up. Even though I Google OEM only I get Amazon oil, mobile one, and other brands .
Just want original fluids so if any one has a 2010 AV and knows the GM Original part #s I would appreciate it if you got back with me.
 
check your owners manual
 
check your owners manual
Your right. We sll should just buy a owners manual so nobody will ask questions on this forum. Then advertisers would not get to people. And nobody would ask questions , and no body would make new friends. I get insulted and feal like Im being talked down to because I do not have a owners manual , ( not yet ). And I guess I should just wait until I get my very own copy. 🥺 whats the point in the AV club than❓
If you or anyone gives a smart comment for me to get a owners manual so I will know how or what to do , others will see what You are. Do you want people joining this club or not?
 
Your right. We sll should just buy a owners manual so nobody will ask questions on this forum. Then advertisers would not get to people. And nobody would ask questions , and no body would make new friends. I get insulted and feal like Im being talked down to because I do not have a owners manual , ( not yet ). And I guess I should just wait until I get my very own copy. 🥺 whats the point in the AV club than❓
If you or anyone gives a smart comment for me to get an owners manual so I will know how or what to do , others will see what You are. Do you want people joining this club or not?
I think the point is he provided you with an electronic version of the manual which is a benefit of this site for those who no longer have one. As far as getting detailed write ups to specific issues or ideas one may want to try, one need look not further than many of @EXT4ME detailed write ups.
 
I don't think it should be required for everyone to purchase an owner's manual.

I did seek out on eBay and purchase one for each of my trucks, along with other factory documentation.

But, that's just the way I roll.

As shown above, there are links to free digital versions both on this forum and through GM online that you can search for on Google.

Those should be sufficient for most people.

I also purchased a full set of factory service manuals that cover both of my trucks in great detail, but that is certainly a bit extreme and an expense I doubt most will go for.

Full blown online in detail service documentation is available for the DIY'er or for anyone that requires such things.

I'm sorry your experience is not what you were hoping for on this forum.

My take on the situation is you were looking for a simply friendly and direct answer for a simple and friendly question, but what you received was not perceived as simple and/or friendly.

Unfortunately, tone and intent are things that are extremely difficult to gauge in written form.

I am getting the feeling that those from both sides are being misconstrued.

Not much I can or care to do about it.

At any rate, I hope you choose to stick around and I hope you find future conversations are more productive and to your liking.

Rest assured, no one here has purposely insulted you over this matter.

However, if that is your perception, it is quite unfortunate and I imagine not much is going to be done about it or change.

I truly hope you have a great day.
 
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