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Call or Text (352) 722-5295Differentials on the 1989-1993 RAM 5.9L Cummins
The rear differential under every first-gen Cummins truck is a Dana 70: full float, 10.5 in ring gear, typically rated at 7,500 lb. Four-wheel-drive models add a Dana 60 front with a 9.75 in ring gear. The rear takes SAE 75W-140 synthetic gear oil. Both axles use a bolt-on differential cover, and that cover is where every service, inspection and gear job starts.
Ratios are the other thing to pin down. The 3.07:1 ratio was common on these trucks, a factory 3.54:1 Dana 70 is documented on a 1993 D250, and a documented 1992 W350 runs 4.10 gears.
What goes wrong
Fluid is the big one. Run a full-float rear too long on old oil and it whines, and towing pushes the heat up. On high-mileage rears with the 3.07 ratio, pitted gear teeth add to the noise. One buyer's guide reports, secondhand, that the first-gen 3.07 gearset is discontinued, so confirm your ratio before you price gears. The documented paths are 3.54 or 4.10 gears in the Dana 70 or, on built trucks, a Dana 80 swap with a locker.
Service parts vs. replacement covers
A routine service needs a gasket and the right oil, and the MAHLE P18562 gasket handles the first part. If you want to replace the factory cover, Mag-Hytec and BD Diesel both build Dana 70 rear covers for these trucks, and Mag-Hytec's 60-DF fits the Dana 60 front. Compare product pages for material, fill and drain provisions and hardware. A cover will not cure worn gears, but the job puts the gears in plain view, which is the easiest inspection you will get on this axle.
What we carry
Covers: the Mag-Hytec Dana #70 rear cover and 60-DF Dana 60 front cover, and the BD Diesel 1061835 Dana 70 rear cover. Gasket: the MAHLE P18562, listed for 1989-2002 5.9L Cummins and several Power Stroke trucks. Hardware: an ATS Diesel Performance 402-009-1000 drain plug for ATS covers and pans. Oil: 75W-140 synthetic from Lucas Oil (10121) and Royal Purple (01301 Max-Gear) for the rear, plus Hot Shot's Secret Blue Diamond and ADRENALINE synthetics in 75W-90, 80W-110 and 85W-140, and Lucas Oil Synthetic 75W-90 and Heavy Duty 80W-90 and 85W-140.
Fitment notes
A 2WD D250 or D350 only needs rear-axle parts. Dana 70 shaft and pinion splines changed during the axle's production run, and Dana 60 units differ by drop side and spline, so match internal parts to your axle rather than the model year. Covers are listed by axle, so a truck running a non-original axle needs its tag checked; verify by VIN either way.
Frequently asked questions
Should I replace the gasket every time I pull the differential cover?
A fresh gasket is simple insurance whenever the cover comes off. The MAHLE P18562 in this collection is listed for 1989-2002 5.9L Cummins trucks. If a new cover ships with its own seal, follow the cover maker's instructions.
Does the front differential cover fit a 2WD truck?
No. A 2WD D250 or D350 has no front differential. The Mag-Hytec 60-DF is for the Dana 60 front on 4WD W250 and W350 trucks.
Can I still get 3.07 gears for a first-gen?
Maybe not easily. One buyer's guide reports, secondhand, that the first-gen 3.07 gearset is discontinued and won't accept standard Dana parts. The documented alternatives are 3.54 and 4.10. Gears are not part of this collection, so call before you plan the job.
Why does this collection include gear oils other than 75W-140?
Because many owners service more than one axle or more than one truck. The rear Dana 70 on these trucks takes 75W-140 synthetic; use the 75W-90, 80W-90, 80W-110 and 85W-140 grades only where your service manual or axle builder calls for them.
Not sure what fits? Call the shop at the number in the header, or use the fitment checker on any product page. We install everything we sell.