11.5 american axle gear oil weight.

[The motor guy]

Why is it that they specify 75w140 for the half ton trucks and only 75w90 for the 3/4 and 1 tons? Ive been running 75w90 in my rear diff which is what it calls for. I change it every 15,000 miles which is what it calls for also. I think 15,000 miles is rediculous but that's besides the point. Anything wrong with running the 75w140? I am using 75w90 amsoil right now. That gear lube is actually sort of on the thin side for a 90 weight. I think its 16.5cst at 100C. There 75w140 is also on the thin side also. It is 24.5cst if I recall correctly. 24.5 is still considered a 90 weight according to the old viscosity chart. What are the benefits of the 90 vs the 140? Other than slight fuel economy gains.
BTW my main concern is to get long life from this unit. I don't believe in saving 2 tenths of a mpg while decreasing the lifespan of my rear diff.

 

[Hemi426]

I have Lucas "Heavy Duty" 80w-90 in my Chrysler 9.25 truck rear end. Are you sure that you didn't get the recommendations reversed? I would think the heavier rear would take the heavier oil but I'm no expert.

 

[The motor guy]

Im sure. They require 75w90 and for it to be changed at 15,000 miles intervals.

 

[The motor guy]

Ive already changed out the factory fill at 15,000. I put amsoil 75w90 in there and will changed out again at 30,000. Is it going to hurt anything if I put a 75w140 instead. I think i am going to send in an oil sample of the 75w90 and also the 140 and see if there is a difference. But I won't do that if my diff is going to blow up from the thicker fluid.

 

[Hemi426]

I wouldn't think your rear end would blow up ,however, you may notice a decrease in your fuel mileage and a slight sluggishness from your ring and pinion having to churn through a heavier gear oil. My advice is to stay with the 75w-90 unless you do a lot of heavy hauling or towing.

 

[The motor guy]

I think im going to step it up to the 75w110 weight for this next change. I think it's a good in between. Then if for whatever reason they quit making the 110 I can still mix the 90 and the 140 to come out with a 75w110. It kind of gives me the best of both worlds. I think these axles were around back in the days or the old spec for differential weight anyways. They probably called for the 90 weight because if they called for the 140 the cst could be as high as 40 cst so that would probably cause problems.

 

[Stewart Fan]

What do you have against the 75w-90? The AAM axle in your Dodge is also used in the GM trucks with the Duramax and the old 8.1 liter has engine. GM also specs 75w-90.

I ran 75w-90 in my '01 Chevy 2500HD with no issues. Towed 7000ish lbs on a regular basis. No axle related issues.

I run 75w-90 in my '07 Ram and it tows an 11,000lb fifth wheel. No axle related issues with my Ram either.

If you spend any time on either the GM or Dodge diesel forums,you find the 11.5" AAM is a very stout axle and seldom fails.

The 15,000 mile interval is nonsense though. On GMs trucks its 50,000 miles. Same axle,two different manufacturers and a 35,000 mile difference in OCI. I'm going to be changing mine at 50,000.

 

[The motor guy]

I thought gm called for 20,000 mile service intervals for the 11.5?

 

[The motor guy]

I just don't think you put a 75w90 gear oil in a differential that has to deal with 650 pound feet of torque. Why do the gas engines get 75w140? All it takes is one good long grade to get that fluid extremely hot and thin it out more than it should be. I prefer the extra cushion of the thicker fluid to keep the parts further apart which would in theory keep it cooler.

 

[Stewart Fan]

AAM rates the axle in our Dodges and the GMs at almost 11,000lbs. Dodge and GM both use the tire capacity to rate them,Dodge is 6200 and GMs are 6084.

The axle is rated about 1.75x more than what Dodge and GM use for their rating. You aren't stressing the axle running the torque of a CTD or Dmax through them.

I'll keep running the 75w-90 until my axle gives me a reason not to.

 

[Jim Allen]

Ditto to what Stewart Fan says above.

A half ton truck with an 8.6-inch ring gear and holding 2.5 quarts of oil is going to run hotter than a 3/4-ton truck with an 11.5-inch ring gear and holding 4 quarts. The need for a thicker oil is more demonstrated.

OIl temp often dictates the viscosity choice and gear size vs the rated load is one of the variables that influences oil temp. There is less tooth contact with the smaller unit so more load is placed on less tooth area and more heat and pressure is developed and you need a thicker oil. The half-tons are obviously running closer to their load limits than the 3/4-tons (have you noticed how much the tow rating have increased on half-tons vs the past?). I think it very likely GM knew exactly what they were doing spec'ing a 75W90 for the 2500. You can double check them by installing an oil temp gauge. If you do, and seldom see temps above about 225 or so, you are good to go with 75W90 IMO.

Going thicker, like a 75W140, won't cost you a thing except fuel economy. More if your diff runs cold (oil more viscous) and less the hotter it runs. Bear in mind a higher viscosity than you need also can increase oil temp a little due to fluid friction.

Bottom line, a 75W140 or 110 isn't going to hurt the axle. If you tow a lot, especially in hot-ol-Texas, it might be a benefit. Thing is, you don't really know unless you've monitored oil temps over a long period. Going solo, based on all the miles I've put of 3/4 and half-ton trucks with oil temp gauges installed, I doubt you need a heavier oil.

 

[meep]

if the gearing is different, the stresses on the fluids will be different. a higher ratio should put less stress on the lubricant, assuming the dia of the ring is the same. The larger vehicle may have higher ratio, maybe a larger ring gear...

My silly little grand cherokee wants 140 weight.... but it has a 3.07 final drive.

M

 

[The motor guy]

What do you guys think about the 15,000 mile service interval? Is stewart Fan right about GM requiring 50,000 mile intervals? I just don't think that every 15,000 is necessary. I figured atleast 50,000 miles. Maybe chrysler just wants more money from service. Even though I change it myself it still takes my time and costs me like 50 bucks. I guess I don't really need to use amsoil but I read in a test that it is the best... Hopefully.

 

[Stewart Fan]

I use either Royal Purple or Mobil 1. Whatever the parts store has on hand when its time to change. Typically the store doesn't have enough of either,so one diff gets RP and the other M1.

 

[Jim Allen]

Originally Posted By: meep
if the gearing is different, the stresses on the fluids will be different. a higher ratio should put less stress on the lubricant, assuming the dia of the ring is the same. The larger vehicle may have higher ratio, maybe a larger ring gear...

My silly little grand cherokee wants 140 weight.... but it has a 3.07 final drive.

M


The differences are very minor. Yes a 4.10:1 gearset will run a little hotter than 3.73:1 but it might be on the order of 5 degrees or less. You'd see a wider variance comparing 2.73s to 7.17s but, yeah, taller gears run cooler than shorter because there is more tooth contact. The load is spread out over a wider area leaving more surface for the oil.

 

[dnewton3]

I'll cut to the chase ...

People often get wrapped up in the dino/synthetic issue in the GM truck world because of the GM "grape juice" diff fluid, which is spec'd by GM# 9986115. So, I did some research. Here is what I found ...

http://www.swedishbricks.net/700900FAQ/Driveline1.html


Eaton actually makes the differential/locker set up, and then AAM buys it and puts it in the axle. If you read that link above, about 1/2 way down, you'll see a copy/paste from an Eaton rep (Michael Asmussen). He clearly states that several different grades of lube will suffice, and also states that both dino and synthetic will suffice. In fact, he basically says to use "GL-5" lube and not worry about it. But, to tow the company line, he does acknowledge that "Texaco" was the OEM lube supplier, and that is all they tested with.

If one wants a heavier lube, then that is fine; I do believe that the actual application makes some amount of difference.
Do you tow?
In what season?
What are the year-round temps you'll experience?
What is the design of your equipment?
Etc.

The 11.5" differentials in the 1-ton GM and Dodge trucks are physically larger, and have more capacity, than do the 1/2 ton trucks. Therefore, the fluids stay cooler in the heavier trucks.

If I towed all summer long in 90+ deg heat, and never saw temps below freezing, I'd opt for a heavier grade lube such as the 110 or 140 grades. But I see temps below zero deg F in my winter 4x4 drives. I also see temps above 100 deg F in summer towing. I need an 'all around' lube grade.

GM, AAM, and Eaton all say that 75w-90 or 75w-140 will suffice, and that is good enough for me. When was the last time you saw one of these HD axles fail from lube grade choice anyway?

 

[The motor guy]

Well looks like I'll use the 75w110 then on the next change. Thanks for the explanation. I think the 110 will suit my needs for 100-110 degree temps in texas and also very cold temps if I ever go up to a cold part of the country. These trucks are so big and can tow so much I don't see why they spec thinner fluids just because it increases fuel mileage if that is their reason. I don't think fuel mileage loss would be noticeable anyways. There are too many other factors to deal with like how hard the wind blows and that type of stuff so you would never notice a gain or loss in fuel mileage anyways. Thanks again for your thorough post.

 

[Dualie]

Originally Posted By: dnewton3

When was the last time you saw one of these HD axles fail from lube grade choice anyway?


well for me it was last week but it was 80K miles with heavy towing and factory fill. so some abuse was involved.

 

[dnewton3]

Originally Posted By: Dualie
Originally Posted By: dnewton3

When was the last time you saw one of these HD axles fail from lube grade choice anyway?


well for me it was last week but it was 80K miles with heavy towing and factory fill. so some abuse was involved.


Do you really believe the failure was due to lube GRADE (by "grade" I'm referring to what most commonly call the "weight"), or was it the 'abuse' and/or lack of OCIs? IOW, if the lube was not changed, and therefore became degraded to a point where it failed to protect, was the the lube's fault, or the owner's for not OCI'ing in a timely manner? Would one blame engine oil for engine failure if the oil was allowed to degrade so badly that it fell way out of grade, and the contamination became too great? You indicate that it was "factory fill" with "heavy towing". Let's not blame fluids for what amounts to neglect. Further, if the factory had installed a 140 grade instead of a 90 grade, that does not mean the failure would not have occured; it just may have taken a bit longer to occur, given the use severity and lack of maintenance.

I'll let you in on another little "secret". It's commonly known among some GM forums that the AAM axles are not always filled as much as perhaps they should be. It's not uncommon to find brand new trucks with less than the full fill. My Dmax 11.5 AAM equipped truck was just one example; it was about 1 qt low upon delivery. I check all fluids the moment I get home (speak volumes for the dealer's "pre-delivery inspection", does it not?). So, it's possible that on top of your heavy-towing, factory fill OCI, you may have been down on fluid from the beginning. Typically, they hold 4 quarts; being down 1 qrt is 25% less fluid to take the heat and loads. How is that a fault of the lube grade?

I owe you an apology up front, because I'm not trying to flame you, but I'm trying to draw a distinction here. (You many not even be the owner; you might be working on it for someone else for all I know). Bottom line: the OEM spec's several fluid options. As long as you use one of those, IN A PROPER MAINTENANCE PLAN, they will suffice quite well. In my mind, 80k miles on factory fill with heavy towing is NOT a maintenance plan. These are NOT, after all, "fill and forget" diffs and fluids.

Back to the OPs question: he can safely use any of the aforementioned grades. He may have to tailor his grade selection to his specific maintenance plan and severity of use. But that is true of ANY product, is it not?

 

[Jim Allen]

Towing at or above the GCVWR can result in oil temps at 325F +. No lube can stand that for long.

According to axle insiders, you wanna know what the most failure prone truck axle is? Dana 80 DRW in motor homes. They are often grossly overloaded and overstressed and neglected.

While doing research for a book, I spent some weeks in a well known axle shop. A 24 foot motor home came in with a raucous howl. Pulling the pan yielded an odor worse than dead bodies in the hot sun (well maybe not that bad, but I've managed to put that experience far behind me). In the oil world, I do believe burned gear oil is the worst possible odor you can encounter. The ring and pinion gears were blue-black, what was left of them. The oil level at or near full but the oil had simply been cooked.

Typically the lighter motor home chassis are near their weight limit once the houses are added. When Ma and Pa get through loading all those "essential" things, plus a full tank of good water from home, that chassis and axle may be well over recommended ratings. I have been told by a reliable source that 375F has been seen in certain motor home axles.

The point is exactly what Dave said above. The oil can handle high temps... for a while... but it breaks down and ceases to lubricate. Failure of the lubricant results in failure of the axle. That is a maintenance or operator failure, not an axle or lube failure, when you get right down to it.

This brings me back to my point about diff temps. If you know what temps you run, you can make a good guess at OCI and at any deviation necessary from the factory viscosity recommendations. I've had diff temp gauges on my trucks for years now, both with and without the very nifty Mag-Hytec covers (which will knock 15+ degrees off temp BTW). With a slippery oil and those covers,even towing, I can run 90 grade oil because they keep the oil temp down to a low level. The benefit for me is slightly better fuel economy but there's no risk because I know exactly what's going on.

Late Addition: Not sure why new trucks would come a quart low, but too much oil in the diff can make it run hotter. I could cite some examples of that, including overfilled diffs that overheated and foamed out the vent. There too low, too high and just right as far as oil level goes.

Here's the AutoMeter gauge in my old Ford truck

Here's the Mag-Hytec cover on the 10.25 in the '86 Ford F-250. It has a built in bung for the temp sensor (not visible) but you can see the ground wire. I also had a gauge with the original cover, welding in a bung purchased from AutoMeter. The cover also adds about 3 qts to oil capacity, which both helps with cooling and extends OCI. Several sources recommended putting the sensor in line with the oil being slung off the ring gear, rather than bulk temp. Seem to read a little higher than bulk but perhaps it delivers a little better picture.

Yeah, I take my gauges seriously. The two at the bottom of the dash are diff temp and trans temp on the "new" '05 Ford. I can also read trans temp off the programmer on the left, but hte gauge reads bulk temp and the programmer reads in the valve body. They are all Isspro. Yes, my name is Jim, and I'm a gauge-o-haulic.

A mild case of what happens to ring gear teeth when the lube fails. I have pics of the aforementioned motor home axle, but they are B&W on film and I'm too lazy to scan the negs.