2nd Gen Non-Engine/Transmission What is the best oil for rear axle

[JR]

A number of studies have shown that 75W-90 really isn't adequate for use behind the Cummins diesel.

The best lube for lightweight/unladen usage is Amsoil Severe Gear 75W-110.

The best lube for moderate to heavy towing and/or high power/torque operation is Amsoil Severe Gear 75W-140.

Any links to said studies? Good ol 90w is still being factory spec'd in many MD and HD rear axles. With lots more torque output than our little ol Cummins.

 

[KATOOM]

I run Royal Purple 75-140 in the rear with a Mag-Hytec cover. No additives needed as the RP recipe contains them. I tow a 14-15k 5th wheel in the summer mountainous terrain in northern CA and I feel its a great product.

 

[JDoiron]

I also use RP 75W-140 with no additives or problems at 175,000 miles.

 

[Bob4x4]

Hi everyone
Wanting to change the gear oil in my 98 2500 4.10 rearend with limited slip. Bought the truck a little over 6 months ago and its time to do that part of the maintenance. As far as I know this may be the original gear oil from 1998, (the tires were not changed since 2000 so you tell me..). I need to know a good rear end lubrication and if I need to use a limited slip additive.
I also am looking for a good transmission shop in southern california (Riverside/Orange county) to beef up the transmission for more power for towing.

the dana 70 and 80calls for 75/140 syn for towing,Alimited slip will need an additive to be used..I always have some on hand if you are local to me

 

[JMcCoy]

Many synthetics are slippery enough without the additive. If you add the additive to a lube that's already slippery enough, it will be too slippery, and you will essentially have an open differential. Change the fluid, but leave room for additive. Drive it and see what it does. If it shatters fluid little at a time until there is no more chatter.

 

[SnoKing]

The best lube for moderate to heavy towing and/or high power/torque operation is Amsoil Severe Gear 75W-140.

That's what I ran in the rear Dana 70 of my 2001.5 for 14 years(Amsoil Server Gear 75W-140). And 75W-90 in the front. It needed a little additive as for the LSD.

Snoking

 

[RustyJC]

Many synthetics are slippery enough without the additive. If you add the additive to a lube that's already slippery enough, it will be too slippery, and you will essentially have an open differential. Change the fluid, but leave room for additive. Drive it and see what it does. If it shatters fluid little at a time until there is no more chatter.

The Royal Purple 75W-140 comes with friction modifier already in it. I used it right out of the bottles with no additional friction modifier and never had any chatter with my 2002's Dana 80. As you say, to add additional friction modifier to the RP before driving it isn't something one would want to do.

Rusty

 

[The patriot]

I changed out my 1998 a while back with Mobil 1, but I forget what weight I used.
I didnt need the LS modifier.

 

[KATOOM]

Many synthetics are slippery enough without the additive. If you add the additive to a lube that's already slippery enough, it will be too slippery, and you will essentially have an open differential. Change the fluid, but leave room for additive. Drive it and see what it does. If it shatters fluid little at a time until there is no more chatter.

Just to clarify something I think a few people may misunderstand..... This is not a bash on synthetics either but merely pointing something out which is significant in the relation between synthetic and conventional and what friction modifiers really are.

Typically there is no decrease in static or kinetic friction when using synthetic lubricants. Although the more uniform molecular structure found in synthetic stocks is what gives the advantage over that of conventional lubricants under extreme temperatures and more capable of low temperature flow properties. The proprietary additives found in X brand lubricants are what people mistake as what the lubricant (oil) is doing but in reality thats not the case. Under normal driving conditions synthetics and conventional lubricants both perform exactly the same. Meaning a synthetic 5-30 and conventional 5-30 will have the same viscous properties at 210* F / 100*C. Synthetics should be used more when extreme hot or cold temperatures are common for the application. Thats not me saying to stop using synthetics either as I believe in using both conventional and synthetics as they both have their place in certain applications.

So in regards to friction modifiers..... The additive you add to a limited slip differential is no more "slippery" than the fluid you're adding it to. If it was then it would be called a friction "improver" instead of a "modifier".....and why wouldn't everyone just fill up all their stuff with friction modifiers instead of regular lubricants. But rather the modification taking place within the friction surfaces is simply because of the ingredients in the additive which have an affinity for metal surfaces. In essence, they're attracted to metal and they change the threshold properties between the transitions of static and kinetic movement in the clutch packs. Also the modifiers contain long chains of poly formulas which are basically sacrificial, and are what breaks down with use as the lubricant performs its job.

I guess in point, synthetic differential fluid requires friction modifiers just as conventional fluid does. Its just that most synthetic differential fluids will already contain the additives in their recipe.

I've used Valvoline synthetic differential fluid in another vehicle and had to add an unusual amount of friction modifier. Even at that the LS wouldn't stop chattering when the differential warmed up. Didn't really care for the stuff either and eventually changed it out for conventional fluid. Yet I'm pleased with the Royal Purple I have in my truck.

 

[SBettencourt]

I used Red Line 75W85 in my '01, no friction modifier required.

 

[fest3er]

... Typically there is no decrease in static or kinetic friction when using synthetic lubricants. Although the more uniform molecular structure found in synthetic stocks is what gives the advantage over that of conventional lubricants under extreme temperatures and more capable of low temperature flow properties. The proprietary additives found in X brand lubricants are what people mistake as what the lubricant (oil) is doing but in reality thats not the case. Under normal driving conditions synthetics and conventional lubricants both perform exactly the same. Meaning a synthetic 5-30 and conventional 5-30 will have the same viscous properties at 210* F / 100*C. Synthetics should be used more when extreme hot or cold temperatures are common for the application. Thats not me saying to stop using synthetics either as I believe in using both conventional and synthetics as they both have their place in certain applications. ...

When they are brand new, both synthetic and conventional lubes will have the same viscous properties. But over time, the viscosity of the conventional 5W30 will increase, and can increase greatly. Why? The primary reason is volatility. Conventional lube is assembled from a range of molecules that average out to 5W30 viscosities; over time, the lighter, more volatile molecules boil off (evaporate) leaving the heavier and longer molecules behind which increases the viscosity. Synthetic lube is built using very specific molecules that are all very close to the 5W30 viscosities; synthetic lube maintains its viscosity far better largely because there are very few lighter molecules to boil off. 'Shear' is another condition that affects a lube's viscosity.

Basic lube is basic lube. The additive packages make the lube do things plain oil cannot. One additive will make the lube achieve a fairly consistent viscosity from -30°C through to 200°C. Another additive will neutralize acids that build up in the lube. Another may coat metal parts with a sacrificial compound that provides some mechanical protection when the system fails to maintain a proper film of lubrication. One additive may greatly reduce washout. Another may greatly resist pound-out. Each special-purpose grease and lube (engine, transmission, differential, wheel bearing, ball-n-socket, open chain, heavy knuckle, etc.) has a unique additive package designed for that specific purpose. The quality of the additive packages is just as important as the quality of the basic oil. Some companies use the best packages available. Some use the cheapest they can get. Most use packages of average quality that generally do an average job of short-ish duration that ensures continued, frequent purchase of the products.

Friction modifiers often increase friction. Synthetic lubes can be so slippery that they prevent clutches from doing what they should. More than one performance transmission builder told me that they don't use Amsoil because it is far too slippery: the clutches (and other parts that use friction to prevent movement) slip under very high torque conditions. But for normal driving conditions, the most slippery lube is to be preferred.

Like everything made by man, some lubes are very good. Some are very poor. Many are 'average'. Some companies strive to build the best lubes available that significantly exceed the relevant specs. Others care only about profit and produce lubes that only barely seem to meet the relevant specs. Most companies generally produce average products that do an average job and encourage repeat business. Some companies have good 'names'. Others have good reputations. Few have both.

We each do our own diligent research and make our own decisions based on what we discover.

 

[KATOOM]

Well put explanation.....and hopefully others understand after reading all these lengthy posts why synthetics offer a longer change interval. Its not that the synthetic fluid is doing a better job under "normal running conditions" but that synthetics can last longer by retaining its original properties over time.

Nonetheless, in regards to the thread topic, I just returned from a camping trip where my truck and trailer gross around 22k pounds. Pulling all that weight in an average 110* triple digit summer heat up 3000 feet in altitude over 100 miles, the differential temperature slowly climbed and remained steady at approximately 210*.