80w 90 or 75w 140

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I have a 2009 Dodge Ram 1500 4x4. I just installed an Auburn lsd and there manual says to use non synthetic 80w 90 and that synthetic is NOT recommended because of chatter, but my Dodge truck manual says to use 75w 140 synthetic. If I use one oil I lose the warranty on the lsd, and if I use the other oil I lose the warranty on the rear. I can buy Royal purple in a 75w 140 non synthetic. What would you do?
 
What is more important? Sounds like you just changed the guts of the rear, so you may have already lost the warranty on it, and seems to me the expensive parts are the LSD/gear mechanism. If that is the case, then Id be sure to ensure the LSD/gear mechanism is warranted.

That said, chrysler vehicles seem to have these lifetime powertrain and similar warranties, and you would want to be sure that they couldnt void it somehow overall if something else went wrong (doesnt seem plausible to me though).

Many syn diff lubes have additives to prevent LSD chatter. Id think that besides maybe an initial dino fill or breakin (go lighter and easier on it), then do some experimenting on the lubes to see if you have any issues with a range of diff lube. Ive never had an issue with mainstream syns in my LSDs. You can change brands and you can add friction modifier as well to adjust the lube properties.
 
I think you already lost the warranty on the rear when you installed the Auburn. I run 80W90 in most of my solid axle rigs. It works well. My Ford still has the factory "trash lock" (which still works though) and it gets the 75w140.
 
If you tow anything I would go with the 75W140. I'm not sure why any company would say not to use syn. I run Amsoil 75W140 in my Grand Cherokee with Detroit Trutracks limited slips in the front and rear. No issues at all.
 
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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Originally Posted By: Zaedock
I think you already lost the warranty on the rear when you installed the Auburn.


Yup, the poster above is 100% correct.

renos09ram;

You have altered/moddified the rear end by changing out the LS unit so your warranty on it( 3/36 and any extended power train warranty )is pretty much now voided. If a non related part to the LS unit fails such as a bearing they are not going to cover that most likely because you got in there and altered it. They "might" but I doubt it unless the dealer installed it. Even if they decided to if they see you went with an 80W-90 conventional instead of the spec'd 75W-140 they absolutely will not cover any of the other parts. Guarantee if you change the LS unit out and run a fluid other than the OE spec one your warranty is long gone.

Just keep in mind the Dodge 1500 rear ends run very hot which is why the OE fluid is a 75W-140 synthetic. You better plan on changing the fluid every 10K or so. I would add a larger aftermarket diff cover to increase fluid capacity and help with cooling.

Also, you said...

Originally Posted By: renos09ram
I can buy Royal purple in a 75w 140 non synthetic.


Where did you see that or who told you Royal Purple offered a non synthetic 75W-140 gear oil? RP MaxGear is a full synthetic synthetic gear oil.

Originally Posted By: RoyalPurple.com
Max-Gear is an ultra-tough automotive gear oil. It’s designed to maximize power and provide unsurpassed protection to heavily loaded gears. It makes gears run smoother, quieter, cooler and longer without overhauls.

Max-Gear outperforms other gear oils because it combines the highest quality synthetic oils with Royal Purple’s proprietary Synslide additive technology.

Max-Gear is recommended for use in truck, motor home / RV, and automotive front or rear differentials, manual transmissions, and lower gear units of marine engines that specify use of an API GL-5 or GL-4 fluid. All viscosities of Max-Gear are formulated with hypoid friction modifiers necessary for use in clutch or cone type differentials. No additional additives are necessary.

http://www.royalpurple.com/gear-oil.html


I don't really know what to tell you. As I said the Ram 1500 rear ends run very hot which is why Dodge spec'd a heavy synthetic gear oil to be used. I would definitely keep it changed often if running a 90 weight conventional oil.
 
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NHEMI- I have a lot of info on the 9-1/4 axle under the half-ton Dodges and nothing I have indicates they run substantially hotter than any other half ton rear axle. They have slightly more hypoid offset than some 1.85-in vs the more common 1.50-in). Is this documented in some way, or just something "everybody knows." I have two file drawers full of axle stuff alone, so if this is a real deal, I want to update my files.

According to the Ford and GM engineers I have spoken with, the reason many current OEs spec 75W140 is that the half tons are rated to tow and carry more than ever before. A load is when a small ring gear axle tends to get HOT. The synthetic 75W140 helps protect the axle in that situation without any cost to fuel economy. If the OP plans to tow/haul a significant period of time, a non-syn 90 grade MIGHT be an issue. If in doubt, the "equalizer" would be the Mag-Hytec cover that offers 3-4 extra quarts and about 15 deg. of temp knocked off. Even better, install a rear axle temp gauge, since the port is right in the cover.

Anyway, I wouldn't go all Chicken Little here over the switch to 90 grade
 
Originally Posted By: Jim Allen
NHEMI- I have a lot of info on the 9-1/4 axle under the half-ton Dodges and nothing I have indicates they run substantially hotter than any other half ton rear axle. They have slightly more hypoid offset than some 1.85-in vs the more common 1.50-in). Is this documented in some way, or just something "everybody knows." I have two file drawers full of axle stuff alone, so if this is a real deal, I want to update my files.

According to the Ford and GM engineers I have spoken with, the reason many current OEs spec 75W140 is that the half tons are rated to tow and carry more than ever before. A load is when a small ring gear axle tends to get HOT. The synthetic 75W140 helps protect the axle in that situation without any cost to fuel economy. If the OP plans to tow/haul a significant period of time, a non-syn 90 grade MIGHT be an issue. If in doubt, the "equalizer" would be the Mag-Hytec cover that offers 3-4 extra quarts and about 15 deg. of temp knocked off. Even better, install a rear axle temp gauge, since the port is right in the cover.

Anyway, I wouldn't go all Chicken Little here over the switch to 90 grade


Seems to be something everyone knows on the Dodge forums.
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My mechanic who is installing this has a co worker who drags alot of cars and he was able to get the Royal Purple 75w 140 in a mineral base. I did order the Mag Hytec cover so it will hold more fluid. I am definitely staying with a mineral base, so do you think I should stick with the 80w 90 mineral base, or if I am able to get the 75w 140 in a mineral base. I am in construction and it's only heavey when I do the demo of either a kitchen or bath and I don't tow. thanks for all the research and replies.
 
renos09ram: I think I'll have to call "Bovine Scatology" on the guy telling you there's a mineral base RP 75W140. I'll gladly eat a crow sandwich later if someone proves me wrong. I don't even think it's possible... strike that, advisable, to make a mineral base gear oil with a viscosity spread like 75W140. If such a thing were possible, it would have to have so many VIIs (Viscosity Index Improvers) that it would be very unstable and shear like mad. If I'm wrong, then this is a teachable moment for me.

An 80W90 should do you fine, IMO. Since you are getting the cover, why not add a diff temp gauge? AutoMeter has some that even say "DIff Temp" right on them and the cover is plumbed to accept them. Not too expensive, either. Then you get to educate us on how hot the Mopar 9-1/4 runs ( : < ). I have diff temp gauges on both my trucks and had them on some GMs as well. Very useful for towing but educational as well. If it turns out you are running hot, you can always go up to an 85W140 mineral oil... but based on my testing and research, you won't have to ... unless you tow a lot.

So what's "too hot?" In my opinion, if the axle stays under 200F in normal solo operation, you have no problems at all and can run a 30-60K mile OCI on mineral oil. If it runs under 180, as most of mine did (do), even better. If it runs above that significantly, then you have to think about things.

Remember that the oil's hot viscosity is graded from it's 210F temp. If you run significantly above that, the oil is thinner than it's grade. That isn't a problem in the short run (depending on how hot... 250F vs 300, for example). At 250, f the oil is running in the 80-85 grade and that's sorta OK but the heat causes the boundary lubrication additives to break down more quickly, hence the need for more frequent OCs. When those additive are gone, the axle starts eating itself up.

In high temp situations, you want to try to stay within the 90 grade if possible, or as close as you can, but if you are combining high heat and a high load, you don't want to be running below that for any length of time and that's where a 140 grade comes in. At 270 or so, it's thinned down to a 90 grade and you still have than minimum of protection. The additive package is still being eaten up by temps, but the axle is better protected until it does.

On the other side of the coil, if you are running a too-thick oil during the 95 percent of truck operation when the axle is below 200F, then that 90 grade might be running as a 140 and the 140 in a higher grade (250 is the next, I think), I haven't actually looked above the 140 grade temps recently. That's extra rolling resisitance from the high viscosity oil and it can is cost you MPG in whole numbers, not the tiny fractions that a thick engine oil might cost.
 
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renos09ram( and Jim Allen );

I am going to defer to JA on this if he says the axles do not get as hot as I have heard about. He clearly is knowledgable about this stuff and to a higher degree than I am. I am just going by what I have heard and been told( Dodge truck specific sites and from dealer not to mention an aggressive/proactive 15K diff service recommended by Chrysler ).

I can only say that is a common concern on the Dodge truck forums with these axles just in general. Replacing the diff cover to increase fluid capacity and cooling is a very popular thing to do. Not just to do it but because of the heat issues( they say ). It is very common to caution against changing when people talk of going to conventional gear oils and/or going to a lighter weight.

I am also going to cry pig poo along with JA about your buddy's claims of a RP mineral base 75W-140. As JA says I will eat crow if shown it exsists but I am not going to skip lunch so I can be hungry enough to eat it. RP 75W-140 is synthetic period.
 
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Hemi, I don't peruse the Dodge boards much, so keep your eyes open in case somebody lists actual observed temps on the 9-1/4 as oppose to just 'Runs hot.. I'm very deep into axle stuff and was even trained to work on those axles. Heck, they should be cool running... one of the biggest ring gears on half-ton axles out there and a fairly large oil capacity stock (compared to the Fords 8,.8 and the GM 8.6, especially). The only thing that could point to higher temps is the hypoid offset... but it's not that much more than what's common these days. There's just no reason I can think of why they would run substantially hotter than anything else out there... but I'm open to the possibility. I'm just not accepting it at face value... hence my spending renos09ram's money on an diff oil temp gauge. Then we would know! ( : < )
 
I have read that the Castrol Hypoy C 80w 90 oil is very good as a mineral oil, would this oil be suitable and what does hypoy c mean?
 
"Hypoy C" is Castrol's schtick, but my interpretation is that it refers to the old "Hypoid" gear oil designation (the way the gears are made.. almost all are hypoid now) and the milspec "Hypoid C/D" gear oil classification. I think it's just a name now, but it's good gear oil.
 
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Originally Posted By: Jim Allen
NHEMI- I have a lot of info on the 9-1/4 axle under the half-ton Dodges and nothing I have indicates they run substantially hotter than any other half ton rear axle. They have slightly more hypoid offset than some 1.85-in vs the more common 1.50-in). Is this documented in some way, or just something "everybody knows." I have two file drawers full of axle stuff alone, so if this is a real deal, I want to update my files.

According to the Ford and GM engineers I have spoken with, the reason many current OEs spec 75W140 is that the half tons are rated to tow and carry more than ever before. A load is when a small ring gear axle tends to get HOT. The synthetic 75W140 helps protect the axle in that situation without any cost to fuel economy. If the OP plans to tow/haul a significant period of time, a non-syn 90 grade MIGHT be an issue. If in doubt, the "equalizer" would be the Mag-Hytec cover that offers 3-4 extra quarts and about 15 deg. of temp knocked off. Even better, install a rear axle temp gauge, since the port is right in the cover.

Anyway, I wouldn't go all Chicken Little here over the switch to 90 grade



When I first read his response, the first thing I thought was how many MILLIONS of the 9.25 came from the factory with nothing more than conventional 80w90! The Corp 9.25 has been used since the mid 1970s, its not like it made it debut in the 2003+ trucks.

Just like the whole G80 Gov-Loc thread the other week...just because the manuals have been updated, doesn't mean those fluids weren't successfully used before synthetics were widely accepted.
 
Originally Posted By: NHHEMI


OY! Not exactly something you want to use as the sole basis for your decision. Highly disputed and contested.


That's true but the problem is that we don't have anything to counter it with. Either Amsoil or their lab outright lied and/or falsified the information, there were some terrible flukes or mistakes, or it's correct. Until we see something done on a similar level, perhaps by a more independent outfit, we have nothing to counter it with but insufficient comparable data from the other oil companies in the test and anecdotal stuff. I don't want to necessarily accept it at face value either but they are the only company publishing comparative data at that level and you have to give it a certain credence. I find it hard to buy into the falsified data thing... too much for them to lose if someone proves they did it. I'm more into thinking some of those results were flukes, which Amsoil would naturally pounce on relentlessly. I could buy into the scenario of 10 samples of a particular oil being tested, and if one sample delivers bad results, that's the one they publish.
 
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