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I have a little over 1000 mi on my truck and I am getting ready to change the fluid in the front and rear differentials, transfer case, and Allison spin on filter. (Already did the oil at 500 mi and plan to change again at 1500)

From reading previous posts I understand that there is some debate on the issue of using anything other than the GM grape juice in the G80 rear differential. I would rather be safe than sorry so I have ordered some grape juice for the rear. Is there any debate (as far as warranty or any other issues) on the use of Mobile 1 75/90 synthetic for the front differential? How many quarts does it take?

Thanks for the help.
 

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The GM in the owner’s manual and the Helms shop manuals refer to a specific API grade or "equivalent" for the G80 axle. I'm one of many on the forum who uses Mobil 1 75/90 synthetic, which, according to GM, is an equivalent lubricant for the G80. I believe the front diff holds 3 quarts. I run Mobil 1 75/90 in the front also.


I don't pull anything at this time, so I'm running 75/90. If I decide to pull anything (5er) in the future, I will replace the Mobil 1 with grape juice. The grape juice has a higher overall operating temperature range.
 

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Isn't the Grape juice 75-90 WT. to?
 

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Dura_Mike, why not just run the grape juice all of the time, rather than switching from one to the other? Just wondering.


Reggie








Dura_Mike said:
The GM in the owner’s manual and the Helms shop manuals refer to a specific API grade or "equivalent" for the G80 axle. I'm one of many on the forum who uses Mobil 1 75/90 synthetic, which, according to GM, is an equivalent lubricant for the G80. I believe the front diff holds 3 quarts. I run Mobil 1 75/90 in the front also.


I don't pull anything at this time, so I'm running 75/90. If I decide to pull anything (5er) in the future, I will replace the Mobil 1 with grape juice. The grape juice has a higher overall operating temperature range.
 

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Reggie1 said:
Dura_Mike, why not just run the grape juice all of the time, rather than switching from one to the other? Just wondering.


Reggie








Dura_Mike said:
The GM in the owner’s manual and the Helms shop manuals refer to a specific API grade or "equivalent" for the G80 axle. I'm one of many on the forum who uses Mobil 1 75/90 synthetic, which, according to GM, is an equivalent lubricant for the G80. I believe the front diff holds 3 quarts. I run Mobil 1 75/90 in the front also.


I don't pull anything at this time, so I'm running 75/90. If I decide to pull anything (5er) in the future, I will replace the Mobil 1 with grape juice. The grape juice has a higher overall operating temperature range.

I can get Mobil 1 for $7 a quart. Grape Juice from GM is $23 a quart. Since I'm not pulling anything right now, it is more cost effective to run the Mobil 1.
Edited by: Dura_Mike
 

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Dura_Mike said:
… the owner's manual and the Helms shop manuals refer to a specific API grade or "equivalent" for the G80 axle
IIRC the last time I checked my 03 manuals ONLY the GM 12378261 lube was specified for the rear diff - the words "or equivalent" were not there. However the "or equivalent" phrase was there for the front diff. That said, according to Eaton (manufacturer of the rear diff .. see post by TxDoc) a GL-5 rated 75W- 90 synthetic is what's required for the rear diff (75W-140 for heavy towing).

 

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Is the Mobil 1 OK for the limited slips also?
 

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st_pinetree said:
Is the Mobil 1 OK for the limited slips also?

According to GM literature, the G80 does not require any additional friction modifier additives for limited slip components. According to the info on the Mobil 1 container, it is suitable for use in limited slip applications. Mobil 1's API ratings match those of GM's "equivalent" lubricant.


My old Wrangler had a Dana 44 with Trac-Loc (limited slip). Daimler Chrysler required a friction modifier additive to be used with the axle lubricant.


I'm sure that GM would like nothing more than to have everyone buy a specific lubricant that they recommend (75/140 grape juice) at inflated prices. Other brands of 75/140 lubricants are $10 to $12 less than GM's exclusive grape juice. It seems pretty odd to me that the lubricant GM recommends is ONLY available at GM stealerships.









Edited by: Dura_Mike
 

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jbplock said:
Dura_Mike said:
… the owner's manual and the Helms shop manuals refer to a specific API grade or "equivalent" for the G80 axle
IIRC the last time I checked my 03 manuals ONLY the GM 12378261 lube was specified for the rear diff - the words "or equivalent" were not there. However the "or equivalent" phrase was there for the front diff. That said, according to Eaton (manufacturer of the rear diff .. see post by TxDoc) a GL-5 rated 75W- 90 synthetic is what's required for the rear diff (75W-140 for heavy towing).


Here are some quotes from the post by TxDoc:
"I noticed in the latest GM owners manual the term "or equivalent" when
referring to the lube specification." "The axle is filled at the factory with a synthetic 75w90 GL5 rating made by Texaco under part # 2276."



Mobil 1 meets or exceeds the synthetic 75w90 GL5 rating.



The "or equivalent" statement regarding rear axle lubricant can be found in the 2003 Service Manual, Volume 1 of 5, page 4-146, near the bottom of the page on the right side. Same info on page 0-42 in volume 1 of 5.Edited by: Dura_Mike
 

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I went to the Chevy dealer today and asked for the correct 75-90 wt. rear gear lube for my 6.6 and he put 4 qts. of Mobil 1 75-90 on the counter. I asked him for the Grape Juice and he said that Mobil 1 is all they use! He wanted to charge me $20.00 a qrt. for the M1. Of coarse I didn't buy it.
 

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Roy C said:
I have a little over 1000 mi on my truck and I am getting ready to change the fluid in the front and rear differentials, transfer case, and Allison spin on filter. (Already did the oil at 500 mi and plan to change again at 1500)
Just an FYI, in case you were planning on having the dealer do it - I just had the dealer do all of that to mine. Total bill came out to $450.75!!!

I usually do all my own maintenance, but figured since they were changing the oil anyways (first oil change was free) I'd just have 'em do the diffs and trans too.

Definitely learned THAT lesson the hard way.
 

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Discussion Starter #13
Thanks for the heads-up Jim but no, I did it myself. Very simple and cost me $20.00 for the Mobil-1. Would have been even easier if I didn't have a skid plate that had to come off first but it was only four bolts.
 

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Dura_Mike said:
.. The "or equivalent" statement regarding rear axle lubricant can be found in the 2003 Service Manual, Volume 1 of 5, page 4-146, near the bottom of the page on the right side. Same info on page 0-42 in volume 1 of 5.
Mike,

Thanks for correcting my error
and the clarification!!
I'm taking my truck to the dealer tomorrow to have a leaking rear axel seal replaced and I was worried they may try to blame the leak on the Mobil-1 75W-90 I put in the rear diff. I'll be sure to have a copy of the Helms manual page you referenced with me. I guess the only thing that might be in question is if Mobil-1 is "explicitly" equivalent" to the GM spec. I can't remember who but someone wrote to Mobil asking if M-1 met the GM spec and Mobil responded that it didn't "explicitly' meet the spec - probably GM's grape color is the only difference.


 

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Dura_Mike said:
[ The grape juice has a higher overall operating temperature range.
It does?

But if it didn't, aren't we splitting hairs here?

Its a RING and PINION, not the Space Shuttle.

Synthetic GL-5 of any make should be FINE.Edited by: Lawnboy
 

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Bill -


Let us know how your rear axle seal problem turns out. My truck has 2250 miles on it and I have a very slight leak on the driver's side rear axle seal and I will be taking it in to my stealer if the leak ever forms a drop. I would be very surprised if GM told you the axle seal problem was caused by Mobil 1. GM's 75w90 "grape juice" has the same GL-5 rating as Mobil 1's 75w90. If GM says there is any warranty problem by this, I would be asking them if they know anything about the Moss-Magnussen Act.


I'm pretty sure that GM has an agreement with Texaco to produce grape juice exclusively for GM. GM can then set the price as high as the demand will allow and they could easily mislead the public into thinking that their synthetic 75w90 GL-5 is better than Mobil's synthetic 75w90 GL-5.
 

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Dura-Mike,

You seem to be contradicting yourself.

One post your claiming that if you'd be towing you'd switch to the Grape Juice, and you downgrade to Mobil-1 while your just solo. Also saying that Grape Juice has a higher operating temperature range.

Now your saying that the Grape Juice is the same as the Mobil-1, and any other Synthetic GL-5 lube.

Where do you stand? On the fence post?

 

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Lawnboy said:
Dura_Mike said:
[ The grape juice has a higher overall operating temperature range.
It does?

But if it didn't, aren't we splitting hairs here?

Its a RING and PINION, not the Space Shuttle.

Synthetic GL-5 of any make should be FINE.

Tom -


I was referring to the 75w140 which has a higher temperature range (able to withstand higher operating temps) than 75w90. IMO you are correct, any brand 75w90 GL-5 should work just fine, but I've used Mobil products forever and that why I use Mobil 1.



Its possible that the Space Shuttle has fewer injector problems than the Dmax....
 

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Lawnboy said:
Dura-Mike,

You seem to be contradicting yourself.

One post your claiming that if you'd be towing you'd switch to the Grape Juice, and you downgrade to Mobil-1 while your just solo. Also saying that Grape Juice has a higher operating temperature range.

Now your saying that the Grape Juice is the same as the Mobil-1, and any other Synthetic GL-5 lube.

Where do you stand? On the fence post?


GM recommends 75w140 grape juice if you are going to do any serious towing. IIRC Mobil does not market a 75w140, but I could be wrong. When I get the fiver, someone's 75w140 will be in the rear axle, until then Mobil 1's 75w90 makes it happen.



My GM stealership refers to "grape juice" as being both 75w90 and 75w140 in the GM product line even though they are 2 different products. Maybe thats where the confusion is?
Edited by: Dura_Mike
 

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Gotcha on the 75/140 vs 75/90 mixup. Sorry!

It IS thick stuff though. Good for heavy towing during the summer heat.

Wouldn't want it in the colder months towing or not.
 
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