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ChevroletGuy
I have a 2001 k2500 suburban w/ 125K and I just have a few questions. I think I'm going to change my differential fluid tomorrow. First off, they say in the owners manual to use 75w-90 synthetic. In my repair manual it says the same thing, but it says with limited slip differential you should add some additive. Here are my questions:
Is it wise to change the fluid, or should I just add some additive?
If I change the fluid, how much will I need to fill it back up?
I have a locking differential, should I add some additive?
If I add additive, what should I use?

Thanks for answering ahead of time!
jmbaker
When I have used Mobil 1 I have never needed to add the LSD additive as it has enough friction modifiers in it already.

As for capacity, I am not sure on a 2500. Been too long since I did one, but guessing ~5 quarts.
Lynn
QUOTE(ChevroletGuy @ Mar 10 2007, 11:48 PM) [snapback]124904[/snapback]

I have a 2001 k2500 suburban w/ 125K and I just have a few questions. I think I'm going to change my differential fluid tomorrow. First off, they say in the owners manual to use 75w-90 synthetic. In my repair manual it says the same thing, but it says with limited slip differential you should add some additive. Here are my questions:
Is it wise to change the fluid, or should I just add some additive?
If I change the fluid, how much will I need to fill it back up?
I have a locking differential, should I add some additive?
If I add additive, what should I use?

Thanks for answering ahead of time!


ChevroletGuy, you'll need 5.5 pints. Just short of 3 quarts.

Lynn
jmbaker
Lynn:

Are you sure about your post above. I thought the 3/4 ton (12 bolt I think) took more juice than a 10 bolt. I am not certain though.
ChevroletGuy
Thanks for your posts guys!

I've been told by a former GM mechanic (he injured his back by catching a falling 4.3L v6 back in '91) tell me that I should just add some GM additive to it and not bother changing it. What do you think?
Scott
QUOTE(ChevroletGuy @ Mar 13 2007, 12:30 AM) [snapback]125220[/snapback]

Thanks for your posts guys!

I've been told by a former GM mechanic (he injured his back by catching a falling 4.3L v6 back in '91) tell me that I should just add some GM additive to it and not bother changing it. What do you think?

That's nonsense - Change it!
Ur2respect
Yea, change it, it's not that hard. If you use certain fluids like Royal Purple you don't need any extra additives even though you have a Limited Slip.
Dave in Mpls
QUOTE(ChevroletGuy @ Mar 13 2007, 12:30 AM) [snapback]125220[/snapback]

Thanks for your posts guys!

I've been told by a former GM mechanic (he injured his back by catching a falling 4.3L v6 back in '91) tell me that I should just add some GM additive to it and not bother changing it. What do you think?


Did he injure his back or his mellon?!?

I'll side with Scott - change it!!

As you said, the 2001 rear differential takes a 75W-90 synthetic gear lube. GM specifies spec 9986115 for the lube. The only lube I am aware of that meets this spec is GM fluid 12378261, which retails for around $22/quart!! Royal Purple verbally claims their synthetic 75W-90 meets the spec, but I have never seen anything in writing to confirm this.

That said, a vast majority of folks are running the Mobil 1 75W-90 synthetic gear lube with no problems. As you are talking about limited slip additives, I assume you have the G80 option. The Eaton G80 is more of a mechanical locking differential, versus a clutch-based limited slip. In any case, if you use the Mobil 1 75W-90 synthetic gear lube, you do NOT need to add any additional additives.
Matt
I have been running Mobile 1 75w-90 for as long as I can remember with no adverse effects...
ChevroletGuy
QUOTE(bekind @ Mar 13 2007, 12:00 PM) [snapback]125271[/snapback]

I have been running Mobile 1 75w-90 for as long as I can remember with no adverse effects...


Do you have the locking differential? (G80)

Dave in Mpls
Yes, I do have the G80 option. If I use mobil 1 do I need to add any additive? The GM additive for the locking differential is only $7.80. Also, when I change it, do I have to jack up each back wheel seperatly to get them to drain out of the axle? I've heard that you need to do that to get it nice and drained.
blindmouse
you shouldn't need any additives, even with the g80. the g80 is a mechanical locker, theres no clutches to engage and all that, so no need for any special additive besides the normal gear oil. with that said, if it would make you feel better, you could add the additive. its cheap enough, and i dont think it should interfere with anything.

in the truck shop here, i've only seen em jack it straight up, drain and fill.
Dave in Mpls
QUOTE(ChevroletGuy @ Mar 13 2007, 12:26 PM) [snapback]125276[/snapback]

QUOTE(bekind @ Mar 13 2007, 12:00 PM) [snapback]125271[/snapback]

I have been running Mobile 1 75w-90 for as long as I can remember with no adverse effects...


Do you have the locking differential? (G80)

Dave in Mpls
Yes, I do have the G80 option. If I use mobil 1 do I need to add any additive? The GM additive for the locking differential is only $7.80. Also, when I change it, do I have to jack up each back wheel seperatly to get them to drain out of the axle? I've heard that you need to do that to get it nice and drained.


If you go with the Mobil 1 synthetic 75W-90 in the G80, you will NOT need any additional additives.

Being you have an '01, the rear differential may have a drain on the underside. If you elect to use the drain (if it has one) I would still recommend pulling the cover to clean off the magnet, inspect, etc. When I service my 1500 rear differentials, I use the factory gasket with a thin coat of Permatex aviation gasket sealer on both sides. Your diff may not utilize a gasket, so check with a dealer on that.

You can certainly jack up each rear wheel seperately to run any lube out of the axles, although I have never done this. It makes sense and certainly won't hurt anything. If it makes you sleep better, knock yourself out. Next service I do I will try it, just to see how much residual lube remains in the axles. I suspect not enough to worry about.
Matt
QUOTE(ChevroletGuy @ Mar 13 2007, 01:26 PM) [snapback]125276[/snapback]

QUOTE(bekind @ Mar 13 2007, 12:00 PM) [snapback]125271[/snapback]

I have been running Mobile 1 75w-90 for as long as I can remember with no adverse effects...


Do you have the locking differential? (G80)

Dave in Mpls
Yes, I do have the G80 option. If I use mobil 1 do I need to add any additive? The GM additive for the locking differential is only $7.80. Also, when I change it, do I have to jack up each back wheel seperatly to get them to drain out of the axle? I've heard that you need to do that to get it nice and drained.


Yes I have the G80 and it operates perfectly with just the Mobile 1 fluid.
ChevroletGuy
Thank you all for your answers. I'm not that ambitious about taking the cover off. I just kind of want to do a quick change. I bought 5 quarts and the additive. I'll probably just take the additive back. I probably won't jack up the wheels either. I'm 99% sure mine has the plug. I'll just pull the plug, let it drip for a while and refill. It's better than nothing I suppose.
jmbaker
QUOTE(ChevroletGuy @ Mar 13 2007, 12:00 PM) [snapback]125295[/snapback]

It's better than nothing I suppose.


Way, way, better than nothing. You should be fine. thumbsup.png
Matt
Hmm, I don't think my rear diff has a drain bolt but my front diff does. I have only changed mine once and then top it off occasionaly.
ChevroletGuy
QUOTE(bekind @ Mar 13 2007, 02:03 PM) [snapback]125298[/snapback]

Hmm, I don't think my rear diff has a drain bolt but my front diff does. I have only changed mine once and then top it off occasionaly.

Well now you got me wondering...I'll have to go check.
carguru
Up through the '02 model year all of the 1/2 tons still had the drain on the bottom of the rear axle. 3/4 ton and above still have the drain.
Dave in Mpls
My '02 has a drain plug, my '04 does not. Most probably discontinued with the '03 changes.
ChevroletGuy
Why did they stop with the drain?

Mine does have it and I'm draining it as we speak.
ChevroletGuy
QUOTE(Lynn @ Mar 12 2007, 08:58 PM) [snapback]125191[/snapback]

QUOTE(ChevroletGuy @ Mar 10 2007, 11:48 PM) [snapback]124904[/snapback]

I have a 2001 k2500 suburban w/ 125K and I just have a few questions. I think I'm going to change my differential fluid tomorrow. First off, they say in the owners manual to use 75w-90 synthetic. In my repair manual it says the same thing, but it says with limited slip differential you should add some additive. Here are my questions:
Is it wise to change the fluid, or should I just add some additive?
If I change the fluid, how much will I need to fill it back up?
I have a locking differential, should I add some additive?
If I add additive, what should I use?

Thanks for answering ahead of time!


ChevroletGuy, you'll need 5.5 pints. Just short of 3 quarts.

Lynn

Man, you were right on the money! I was right on my 3rd quart and it started pukin out a little bit so I let it sit for a bit to get any excess oil out and then put the plug in. Took me 1/2 hour because I let it sit to get all of the old stuff out. VERY EASY JOB! Thanks guys! good.gif
carguru
QUOTE(ChevroletGuy @ Mar 13 2007, 06:21 PM) [snapback]125319[/snapback]

Why did they stop with the drain?

Mine does have it and I'm draining it as we speak.


The 14 bolts still have it. GM discontinued it in late '02 on the 10 bolts as part of the cost reduction effort. They just changed it back to the way things were before '99.
ChevroletGuy
I'm sure it didn't save them THAT much money. Oh well, people should probably check things out anyway when changing it.
Lynn
Guys, here is part of a 2005 White paper on differential wear that explains why you should change your differential fluid after a few thousand miles. It's on the AMSOIL TSB section and I can provide you with the link if you'd like.

Short version: "The importance of changing the factory fill break-in gear lube within the first few thousand miles was proven in a field test using four similar vehicles. Oil analysis confirmed that most of the wear occurs during the break-in process and that the oil should be changed for optimizing differential life."

Seems to me that since most wear occurs within the first few thousand miles, the longer we leave all those shavings in the diff lube the more wear we'll have. The person who recommended just adding some additive and leaving the old fluid in place needs to read this.

Hope this helps.

Lynn good.gif
Ken
thanks Lynn - never seen a recommendation to change the diff fluid after break in but I suppose it makes sense. I will have to do this soon.
ChevroletGuy
I never get to buy new vehicles so I just have to hope that it was changed after break-in. That makes complete sense though. They tell you to change the oil right away too in the engine because of shavings, it just makes sense to do that to the differential too. Don't you think that someone one should do that to all enlcosed mechanics? ie:(tranny, all differntials, transfer case, etc.)

EDIT: The guy that said to add additive (which is my girlfriends dad) has a philosophy where he doesn't fix anything 'til it's broke. I, for one, hate that. I like to take every precautionary measure I can. Changing fluids, lubing stuff, replacing worn parts. It just keeps a good state of mind instead of the, "Am I going to break down on this trip" feel. I'm glad I have this forum otherwise he'd probably talk me in to not doing anything. Thanks everyone!
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