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Rear diff oil

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Old 12-04-2010, 03:47 PM
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Default Rear diff oil

Probably this question has been asked before, however i want to change the oil in the rear diff, and the dealer wants to much money! Now i have done some research and i cant decide on what kind of oil should i use on my rear diff and how many qt does it take.
What is everyone using? and not void the warranty in the same time!
Amsoil, lucas, royal purple, mobile1 , valvoline... mopar...

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Old 12-04-2010, 04:20 PM
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You need to use something that matches the manufacturer spec (MS-8985) I used Valvoline SynPower when I did mine. I think it took 3-4 pints but I don't remember for sure.



Rear Axle MOPAR
Synthetic Gear Lubricant SAE 75W-140 (MS-8985). Limited-Slip
Rear Axles require the addition of 118 ml (4 oz.) MOPAR

Limited Slip
Additive or equivalent.

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Old 12-04-2010, 06:03 PM
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You should use a good quality, name brand, 100% synthetic.

I currently have Royal Purple in my front differential, but I am using Lucas CONVENTIONAL in my rear differential. I am doing so because I have an aftermarket LSD which STRONGLY specifies a non-synthetic for proper operation.
I really weighed out whether or not to do this in the rear differential, but after talking directly to Auburn Gear, I went with the Lucas conventional.
To offset not using a synthetic in the rear, I change the fluid at 15k miles (and add 4 oz. of friction modifier). For the front, because I am using a full synthetic, I change at 30k mile intervals or every other time I change out the rear.

Unless you run a LSD which specifically calls for a conventional lubricant, stick with the synthetic at 30k, or go to 15k if you tow/haul regularly...
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Old 12-04-2010, 07:48 PM
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I have talked to some people and they have told me amsoil is the best. I guess is a matter of preference. I do a little bit of towing, but not that much to make a huge difference.
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Old 12-04-2010, 09:53 PM
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Quote:
Originally Posted by ram09red View Post
I have talked to some people and they have told me amsoil is the best. I guess is a matter of preference. I do a little bit of towing, but not that much to make a huge difference.
Just make sure that they list MS-8985 as a spec they meet if you like your warranty.
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Old 12-05-2010, 08:10 PM
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I did alot of research and you have to use a 80w 90 mineral based gear oil if you have the Auburn limited slip. My opinion on Lucas oil is that it is junk. I had it in my other truck and when I went to change the fluid it came out very foamy. Here is a link that shows why
JHZR2 & wm1998: I know exactly why this company cautions against synthetic and I got it from the horse's mouth. Here's the skinny.

This is a cone clutch limited slip, currently the only such unit on the market. Instead of clutch plates, it uses a cone shaped member combined with the side gear that fits into a recepticle and the friction between those two parts is what provides the axle torque (braking) for limited slip operation. You can see an exploded view of the unit here, as well as an explanation on how it works:

Auburn Insto

The bias ratio of the unit is calibrated on a certain friction coefficient, so the first thing that happens with a synthetic is a loss of bias ratio (the unit is less effective). The next thing that happens is a polishing of the active surfaces of the two clutch members and this further reduces the bias ratio. Once that surface is altered, that loss is permanent. Unless, I am told, you dismantle the unit and rough it up again. I was told that Auburn Gear has experimented with some types of synthetics. I was told that they are looking into the issue again and if I hear anything, I'll pass it along.

How do I know this? Look at the byline on the attachment.

To the OP, I would use a 80W90 mineral. That's what the engineers at Auburn Gear installed into my truck when they installed my unit. The 2.5 and 3.5 bias ratios Auburn advertises are calibrated on a Chevron 80W90 gear oil, so you'll get the advertised performance on that oil... with the correct amount of friction modifier of course (which comes with the unit).

Does RP have any non synthetic oils? I don't think so, nor do I think there are any non-suyn 75W140 oils.

PS: wn1998: Detroit recommends mineral oil for Truetracs as well. Synthetic do reduce the bias ratio of that unit as well because friction is what is'a all about in that apparatus. There can be adverse symptoms too, such as odd noises and squealing but not always. Anecdotally, we know some syns produce no adverse noises in Truetracs, Amsoil is one. I have a Trutrac in another truck and had Amsoil in it for a time with no noise. Someone at Eaton knows more about which oils cause this but they won't name any names. Rumor has it that it's Redline, but I have never been able to verify that. Any Truetrac owners out there running Redline?
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Old 12-05-2010, 09:28 PM
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I have an 09 ram hemi,3.92 with a detroit truetrac and amsoil severe gear 75-140, no noise or issues at all.The Eaton tech told me they have had issues with synthetic lubes in the past.He said if it made any rude noises to switch back to dino lube. That was one yr. ago.
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Old 12-05-2010, 11:47 PM
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It may not make noise but your probably not using the lsd to it's full potential by using synthetic.
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Old 12-05-2010, 11:47 PM
 
 
 
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