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2003 chevy trailblazer_ls
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Discussion Starter #1
Is this the plug used to refill rear end?
we can see the spring- and the rear end. looks like a simple socket extension would do?
 

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2004 chevy
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191 Posts
Yup, that's it. Just use the square drive of an extension to loosen it. I believe it is a 1/2" drive that fits it.

Pull the rear cover, clean everything up real good and put the cover back on with a new gasket. Then fill through that hole with new oil and you're done. You will want the vehicle level when you are filling it.
 

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2002 chevy trailblazer_ls
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Yep. You may have a drain plug too. 2002's do. I think it's a 3/8" square drive. Some can be difficult to loosen. So be sure you can get the filler plug loose first before you drain it!



 

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2002 gmc envoy_slt
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I can confirm it is a 3/8".

My fill plug was really tight and I almost striped it. I got a new 3/8" breaker bar at SEARS and that did the trick. Some tools have sharper corners than others. My Craftsman extensions were kinda rounded on the corners so that was part of the problem.

I ended up getting a new plug at the dealer for like $4
 

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Discussion Starter #6
ill have to check and see if there is a DRAIN plug.
so its 3/8 for both drain and fill?
does this oil also flow easily?
Do I HAVE to remove the rear cover?
 

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2003 gmc envoy_slt
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Gear oil should drain fine unless some abnormal conditions have occurred.

At some point I think pulling the cover to check and clean out any deposits/debris is a good idea.... however when I did, the cover gasket listed at most parts houses didn't fit my 03 Envoy. Since it was an 80-100 mi. trip to the nearest parts store, plus I still don't know the correct gasket p/n, I just reused the old gasket. So far no problem.
 

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does this oil also flow easily?
Do I HAVE to remove the rear cover?

Yes it will flow. Drive it a few min to warm up the oil first if it's cold.

No you don't have to remove the cover is there is a drain, or if you have a Mity Vac or similar to pull it out through the filler. You can only get to a small area of the inside surfaces of the diff to wipe off residue if you do take the cover off. With a drain plug, you could drain it, fill, drive a couple of days, drain again to get the old stuff left residue etc picked up in the new oil, and do a final refill.
 

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Discussion Starter #10
absolutezero- you use a new gasket?
how easy a job?
 

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absolutezero- you use a new gasket?
how easy a job?
I bought a new gasket but it didn't fit. Unfortunately it's a the cabin so I can't tell you for sure the Felpro number BUT it was the only one listed at both rockauto and checker auto(partsamerica). I ended up reusing the original gasket and no problem. I'd suggest pre-buying the gasket and hold up to the exterior bolts to see if it's correct. The bolts have some thread lok on them and will come out semi-hard all the way. If you have a bottom drain plug, of course, drain the oil first.
If you can pick up one of those gear oil pumps, the kind that goes in the bottle, it makes refilling easier. You'd need a 2 qts of gear oil and will have a small amt. left over.
Base on research done by tblazed I used Royal Purple synthetic gear oil. The genuine GM stuff is pricey, around $25/qt.
 

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Discussion Starter #13
from tha manual-
SAE 75W-90 synthetic axle lube.
GM part # 78261

or lube meeting GM Spec 9986115

this what youre referring to?
 

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2003 gmc envoy_slt
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from tha manual-
SAE 75W-90 synthetic axle lube.
GM part # 78261

or lube meeting GM Spec 9986115

this what youre referring to?
Yes... turns out 12378261 has been replaced by 89021677. Often it's referred to as "grape" juice 'cause it actually smells like it. I emailed Mobil thinking their axle lub would meet GM specs, answer = no. I did find out Texaco was/is the supplier but couldn't find a discounted source. As stated tblazed also was researching this too. A rep from Royal Purple told him their gear oil did meet GM's specs but it doesn't say so on the bottle. Probably one of those mysteries of life we/I won't live long enough to know the difference!!
I got the RP @ NAPA. Don't recall exact price but around $10/qt
 

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Discussion Starter #15
what about when you put the screw back in, you guys using teflon tape?
especially on the one pointing downward?
 

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2002 chevy trailblazer_lt
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Yes... turns out 12378261 has been replaced by 89021677. Often it's referred to as "grape" juice 'cause it actually smells like it. I emailed Mobil thinking their axle lub would meet GM specs, answer = no. I did find out Texaco was/is the supplier but couldn't find a discounted source. As stated tblazed also was researching this too. A rep from Royal Purple told him their gear oil did meet GM's specs but it doesn't say so on the bottle. Probably one of those mysteries of life we/I won't live long enough to know the difference!!
I got the RP @ NAPA. Don't recall exact price but around $10/qt
So you are saying the Mobil 1 gear oil does not meet GM's specs? I thought I have read many times on this board that it does?:confused:
 

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So you are saying the Mobil 1 gear oil does not meet GM's specs? I thought I have read many times on this board that it does?:confused:
It was a couple years ago I started looking. At that time, as stated, I emailed Mobil 1 with an inquiry and as stated the answer was "no" it doesn't meet the reference GM spec. Also there was nothing on the product bottle at that time stating it met the specs. I haven't looked lately so things may have changed. This doesn't mean Mobil 1 is bad. Unfortunately I couldn't find or find anyone who knew what the details of the specs were or what portion of the spec that Mobil 1 did not meet.
My Dad often would say, son, 100 years from now you'll never know the difference! I suspect using Mobil 1 falls into that category! Since tblazed had a favorable reply from Royal Purple and it was available, that's what I used.

To answer the question about using teflon tape..... the plugs are tapered and no tape seal is required.
 

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Your DAD is a smart man. Listen to him. I have a feeling that ANY good high quality synthetic 75w-90 gear oil will work in these type cars. Whether it has a G80 LS or not. TBSS is a different story they have some issues with the axle. But a I6 or 5.3 real axle should work with, like stated above HIGH quality synthetic. If I were to use MB1 75w 90 synthetic and another uses Valvoline and another the grape juice from GM. Which is their dye color to tell the difference, probably for warranty issues. And no problems, the what of it? Its been stated on here many time that people have used MB1 without any problems. I guess we could get into splitting hairs over this issue. The same as antifreeze which some said earlier we could not use Prestone DEX-COOL. But when I found the GM bulletin that said any DEX-COOL brand that had printed on the bottle GM6277M could be used. rbarrios then changed his and everybody now will use that. Folks, find a good high quality synthetic (MB1, Valvoline, Castrol, RP, Amsoil) and go with it. And we should ask questions about what we should use in our cars and use the best we can get. Yep, here is a mystery in life. A Ford owner will use a FL1-a oil filter from the dealer thinking its better because he bought it at the Ford dealer, when he can go to NAPA and purchase a NAPA Gold made by WIX.:confused: The company I work for has fleet Ford trucks and they use NAPA oil filters instead of Ford....Go figure.....:m2:
 

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If I recall correctly, the reason I went with Amsoil and not with Mobil one, was that, at the time the MO was only a synthetic blend, and not a full synthetic. This was actually pointed out to me by the parts guy at chevy. Don't know if mobil makes a fully synthetic lube now though....
The drain plug does make it really easy too!
 

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how many quarts do you use or do you just fill till you cant anymore??
 
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