Hello;

I think I do not have a limited slip (LS) rear axle in my truck but want to bounce that off the forum. I also am looking for fluid recommendations.

My truck: 1999 Dodge Ram 2500, Cummins, 4x4, Quad cab, 5 speed manuals transmission

The glove box tag says the following for my axles:

DJF --- front axle (DANA 60F)
DRL --- Rear axle (DANA 80 Hybrid)

When I look in the factory service manual, I see nothing like these codes! It talks about a 286-RBI for the rear (in both the LS and open axles) and a 248 FBI for the front.

When I go to this webpage I learn more:

http://dodgeram.info/tech/BRSpecs/fluids/specs.html

Looking at the webpage along with all the other info I feel confident I have the 286-RBI rear axle; but how do I know if it is a LS or "open" prior to opening the differential cover? The webpage only gives information to add friction modifier to the DANA 80 axle, so does that mean I have a LS?

I plan to change the fluid soon to both these axles, and I'd like to know ahead of time what all I need. (friction modifier or not?)

Also, any recommendations for gear-oil? I used to use Castro Syntec gear-oil and have been happy with it; but I have not been able to find it anywhere

Thanks in advance for any and all replies.

--Matt

 

The glove box sticker will have the words anti-spin. My 2WD has three entries for axle on the sticker:

Axle: Dana 70
Axle: 3.55 ratio
Axle: Anti-spin differential


Another way to find out is to chock the front tires, jack up the rear end, and support it on jack stands. Then with the park brake released and the transmission in neutral, spin one of the rear tires while watching the opposite side. If you have a LS diff, the other tire will spin in the same direction. An open diff, the tires will spin in opposite directions.

Use the friction modifier only in the LS diff if you have it, it is not needed in an open diff. If you do need it, do not use the whole bottle. You only add a few ounces at a time, and then drive the truck. Do a few tight figure 8 turns. If the rear end feels too "grabby", or you get wheel hop during the turns, add a little more and try again. Adding too much keeps the clutches from doing their job effectively and they will slip too much.


I used Valvoline synthetic in my rear axle on the last change. If you don't tow anything, use 75w90. If you do tow (or tow heavy) use 75w140. No problems using the thicker oil while unloaded, it will only get as thick as it needs to based on oil temperature (heavy loads=higher differential temperatures). The service manual calls for 75w140 only in the front axle.

 

Actually the thicker 140 weight will always run hotter than the lighter 90 weight simply because of the added friction as the thicker fluid is pushed around by the hypoid gear action. Also, because thicker fluid doesn't dissipate the heat as fast as the lighter fluid the 140 will run hotter under lighter loads.

This doesn't mean you shouldn't use 140 but rather that the decision to use it shouldn't be based merely on the fact that you have a heavy trailer behind you. There are MANY more variables involved, but generally the lubrication engineers allow for consumer ignorance by making fluids more applicable and/or tolerant to a wider range of applications.

That said, I run a synthetic 75-140 in the rear but I've toyed with switching back to a 75-90 or 80-90 simply because I'm curious to experiment with differential temperatures. The stuffs too expensive to toss in and out just for fun.

 

Thanks to both of you for the replies! I am confident now that I have an open rear-end.

I have used Valvoline oil in almost all my vehicles (gas-powered) for years and have been very happy with it. I was actually considering their synthetic gear oil. I think that's the direction I will go.

Previously I used 80w-90 syntec in both the front and rear axle. That was 50,000 miles ago... No issues. I'll change out to the 140 in the front axle just to match factory specs. I don"t tow heavy very often so Ill just stick with the 90 weight in the rear.

Just curious, what would you consider "heavy" towing? I pull my single axle trailer quite often to move mowers and long pieces of lumber, but I would guestimate it to be only 1500-2000#'s. Once in ahwile I use a 20' flatbed to move a tractor but that is only 1-2 times a year.

Thanks again for your input.

--Matt

 

You're welcome, and jrs_dodge_diesel is a very smart individual offering some good information.

But in regards to what's "heavy towing", that would be more in the range of trailer weight up around the towing capacity of the truck. And....if the ambient temperatures are close to triple digits while towing and/or in more mountainous terrain.

I dont think a couple thousand pounds behind your truck constitutes as heavy.

 

Thanks again.

My single axle pulling is probably more like 2000-2500 #'s, but I still don't think that is too bad either.

My 20' flatbed is used to haul a 50 HP tractor that weighs about 7K, so plus trailer weight that is at least 8K. I would consider that heavy, but since I only do that a couple times a year I think I will be fine with the lighter oil.

Thanks again,

Matt

 

Thanks KATOOM You're pretty sharp on these trucks too!

It has been a while since I measured my axle temp (IR thermometer) when towing long range, but I don't recall the temps being excessive. They stayed below 200º while towing in ~95º weather. That IR thermometer was also handy for checking wheel bearing temperature too.

I went with the 75w140 because I was towing long distance and didn't want to risk the extra wear and tear on the gear teeth if the lighter oil wasn't up to the task.

Another thing I'd like to point out. Make sure that whatever gear oil you choose has a rating of GL-5. And double check the capacities for you axles in the manual. Each axle (Dana 60/70/80) has different capacities.