The 2015 4th Gen Ram 2500 farm truck gets used a lot around here. So much so that I didn’t even notice when the 150k mark came and went. But when I did notice at 160k, I asked myself a few questions. Namely, have I ever changed the drivetrain fluids?
I’m pretty sure the answer is no. Although the 6.7 Cummins has enjoyed regular oil and fuel filter changes, the drivetrain has not. And now it’s time to catch up on some long-overdue maintenance, like swapping the fluid in the front and rear differentials, the transmission, and the transfer case.
Choosing the Right Fluids
RAM did a ‘great job’ on page 250 of the manual, where they specify the fluid types but mention no quantity amounts. They also specify a specific MOPAR fluid for the transfer case. (A very expensive one at that..) I broke it down below and will make a few recommendations for what I am using to get the job done.
I will add that getting a straight answer on capacities and fluid suggestions is an absolute fool’s errand online. So, I deciphered the above in the chart below and made a few suggestions while avoiding overpriced fluids. The capacities listed are from practical experience during the change. The products I use are non-expensive, readily available fluids that work great in racecar diffs and transmissions and will be fine in the 6.7 Cummins drivetrain.
| Location | Specification | Capacity (Quarts) |
|---|---|---|
| Front Diff | Synthetic GL-5 SAE 75w-85 | 2.4 |
| Rear Diff | Synthetic GL-5 SAE 75w-85 | 4 |
| Manual Trans (G-56) | Mopar ATF+4 | 6-7 |
| Transfer Case | Mopar BW44-44 | 2 |
My Recommendations
- Front Diff and Rear Diff – I have a bunch of Mobil 1 75w-90 and Valvoline 75w-90 from racing that I will use. There is no need for anything exotic here. Anything that is a synthetic GL-5 75w-85 or 90 will work fine.
- Manual Transmission and Transfer Case – Valvoline ATF+4 will work great in both the transmission and transfer case, and the cost is significantly less than the Mopar offerings. (The BW44-44 is over $50 per quart.) Don’t overthink this one. Many people blend multiple oils or buy $30+ per quart oils. All of it is overkill. ATF+4 works great.
Maintenance Intervals
This is where I dropped the ball. My 4th gen has the 6.7L Cummins Diesel mated to the G56 manual transmission. I change the engine oil every 15,000 miles and alternate between changing one of the two fuel filters. However, I haven’t touched the differentials, transmission, or transfer case during this time. They have all racked up 160k miles on the original fluid. Below are the maintenance charts from the manual.
First up is the differential interval. I know 150k miles is too much, but a 24k-mile or 12-month interval for differential fluid is absurd. This is a great money maker for the dealerships. Going forward, I will change the differential fluid every 75k – 100k mi, especially considering how well the original fluids held up.
Below is the transmission interval. This seems right, and I will change the transmission and transfer case fluids every 100k miles.
Changing the Front and Rear Differential Fluid (the easy way)
Tools Required:
- 3/8″ ratchet
- Oil transfer pump
- 4 quarts of diff fluid for the front diff
- 2-3 quarts of diff fluid for the rear diff
I started with the rear differential, and I was immediately shocked to find that the diff cover did not have a drain plug. The ‘proper’ method to drain the differential is to remove the diff cover. This requires removing a bunch of bolts and letting the fluid fall out. Then you dry the reusable gasket, clean the mating surfaces, and reinstall the gasket and cover. Finally, everything is bolted back together before filling the diff back up.
No, No, No. Let’s cut this 1+ hour job down to 10 minutes.
To do this, remove the fill plug with the 3/8″ ratchet and insert the suction side of the transfer pump through the port. It is very easy to feed the line in, and it will easily push to the bottom. Then pump the fluid out. I used a marked bucket to see how many quarts came out. After removing 4 quarts of old oil, I poured 4 quarts of new oil in. Wipe off the fill plug, reinstall the plug, and you are done.
Repeat the process for the front and change both differential fluid sets in under 30 minutes.
(Note: I found it funny how everyone removing the diff cover online states, ‘Now is a great time to inspect the condition of the differential.’ … For what? … I have never once had to ‘inspect a differential.’ It is not a traditional wear item; it either works great or quickly lets you know something is wrong. They don’t fail slowly.)
Changing the G56 Manual Transmission Fluid
Tools Required:
- 14mm hex head socket 3/8″ or 1/2″
- 7 plus quarts ATF+4. I am using Valvoline as it is $30 per gallon.
- Oil transfer pump
Now we are talking; no corners are cut here. This transmission is equipped with both a fill and a drain plug. The standard procedure is to remove the fill plug first. It’s no use draining the transmission to find out the fill plug is seized.
After removing the fill plug with the 14mm hex, remove the drain plug and be ready to catch the oil. It dumps fast. Clean and reinstall the drain plug once the oil drain slows to a drip or stops altogether. I tighten the plug snug by hand and then a quarter turn with the ratchet. (It gets tight quickly, so be careful not to overtighten.)
The transfer pump is then used to transfer the ATF+4 fluid into the transmission through the fill port. Add fluid until it begins to leak out of the port. Finally, clean and reinstall the fill plug and you are finished.
Changing the Transfer Case Fluid
Tools Required:
- 3/8″ ratchet
- 2 quarts ATF+4
- Oil transfer pump
Change the transfer case fluid just like the transmission, except we will use the 3/8″ ratchet to remove the fill and drain plugs. Once again, the oil dumps fast, so be ready. Once the draining finishes, reinstall the drain plug, pump ATF+4 fluid into the transfer case until it overflows the fill port, and then reinstall the fill plug. It’s that easy.
Conclusion
First, don’t overthink it and get stuck in the collective analysis paralysis online. Simple oils for a simple drivetrain work. Sure, some exotic, overpriced blend may anecdotally make some think the shifts are smoother, but none of it is quantified, except in extra dollars spent. Second, there is a lot of wiggle room in the fluid change intervals, as evidenced by how good my 10-year-old 160k-mile fluids looked and functioned. However, I plan on doing a little better and changing them again after another 100k miles. And finally, if you don’t get hung up on the process and can live without ‘inspecting’ your already working perfectly fine gears, you can finish all of these in less than an hour with a slight adjustment to the process.
