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If you own a second generation Ram with a Cummins, you have one or the other. The NV4500 was the manual from 1994 to about the 1999 model year behind the 5.9L diesel, and it stayed behind the gas V8 and V10 for a few more years. The NV5600 took over behind the Cummins in mid 1999 and stayed until the G56 replaced it in 2005. Both are iron case, both are heavy, and both have strong followings. They are very different boxes to live with.
Side by Side
| NV4500 | NV5600 | |
|---|---|---|
| Speeds | 5, with deep granny 1st | 6, with overdrive 6th |
| Ram years (Cummins) | 1994 to early 1999 | Mid 1999 to 2005 |
| Overdrive | 5th, about 0.73 | 6th, about 0.73 to 0.79 depending on version |
| Torque capacity | Good for stock and mild power | Higher, built for the HO Cummins |
| Signature failure | 5th gear nut backing off | Input shaft and bearing wear, 6th gear issues |
| Rebuild difficulty | Simple, well documented | More involved, fewer people do them |
| Parts supply | Excellent | Good but pricier |
Ratio numbers vary with year and version, so treat the table as a guide and check the tag. The overall story holds: the NV4500 is the simpler box with a granny low, and the NV5600 is the stronger box with a better spread for highway towing.
NV4500: Simple and Tough, With One Big Weakness
The NV4500 is the box a lot of builders swap into other trucks because it is compact for what it handles, easy to rebuild, and parts are everywhere. The deep 1st gear makes it a crawler's favorite. On a stock 12-valve or early 24-valve Cummins, it lives a long life if the fluid is right and the 5th gear nut is tight.
That nut is the weakness. The 5th gear retaining nut can back off, and when it does the 5th gear and synchro walk off the mainshaft. The first sign is often 5th gear going away or a buzzing from the back of the box. Ignore it and you wreck the gear, the hub, the shaft and sometimes the case. Our NV4500 5th gear nut guide covers the fix and the upgraded nut.
Past that, NV4500s wear synchros like any manual, usually 2nd and 3rd first. A complete Dodge NV4500 synchro ring kit or the GM version covers every gear during a rebuild. See NV4500 rebuild cost for real numbers.
NV4500 and NV5600 Parts
Synchro kits, input shafts and shifter fixes for both boxes.
NV4500 Synchro Kit → NV5600 Shifter KitNV5600: Stronger, Smoother, Costlier to Fix
The NV5600 handles more torque, which is why Dodge paired it with the high output Cummins. The extra gear gives a tighter spread, so a loaded truck stays in the power band better on the highway, and the 6th gear overdrive keeps cruising RPM down.
It is also more expensive to keep healthy. The most common complaints we see are input shaft and bearing wear, gear noise that changes with the clutch, and upper gear trouble on trucks that towed hard in 6th. Like the ZF6, towing heavy up grades in the overdrive gear is hard on it. The NV5600 also tends to get blamed for dual mass flywheel and clutch noises, so rule those out first. Our NV5600 problems and cost guide goes through each.
A cheap and common NV5600 fix is the shifter. The factory tower linkage wears and gets sloppy, which leads to missed shifts. Our NV5600 short throw shifter kit replaces it. For the NV4500, the matching fix is the NV4500 shifter tower and bushing kit.
Which One Should You Want?
Pick the NV4500 if you crawl, work off-road, want a box you can rebuild in the garage, or are building a swap where size and parts cost matter. Keep power reasonable, use the right fluid, and fix the 5th gear nut before it fails.
Pick the NV5600 if you tow heavy at highway speed, run more power, and want a smoother gear spread. Budget more for repairs and find a shop that actually rebuilds them before you need one.
Swapping one for the other in a Ram is possible but not bolt-in. The case length and crossmember position differ, so the driveshafts need changes, and the shifter location moves. Most people are better off fixing the box they have.
Fluid for Both
Both boxes are fussy about fluid. Check the tag and owner manual for your year, because the factory spec changed over time. Wrong fluid shows up as notchy cold shifts and faster synchro wear. Our NV4500 fluid change guide covers capacities and the fill procedure, and our GL-4 vs GL-5 guide explains why the oil type matters.
Rebuild Cost Comparison
| Job | NV4500 | NV5600 |
|---|---|---|
| Shifter tower or short throw kit | $100-$250 | $90-$250 |
| Bearing and synchro rebuild, parts | $300-$700 | $500-$1,100 |
| Shop rebuild, out of truck | $1,500-$2,600 | $2,200-$3,800 |
| Remanufactured exchange unit | $2,000-$3,200 | $2,800-$4,500 |
Ballpark numbers. Add removal and install labor, and on 4x4 trucks the transfer case comes out too. Parts for both are in our rebuild kits and hard parts sections, and our sister store CoreTransmissionParts.com carries more.
FAQ
Is the NV5600 stronger than the NV4500?
Yes. The NV5600 has a higher torque capacity and was paired with the high output Cummins. The NV4500 is plenty for stock and mild power and is simpler and cheaper to rebuild.
What years did Dodge use the NV5600?
Behind the Cummins from mid 1999 through 2005, when the G56 replaced it. The NV4500 was used behind the Cummins before that and behind gas engines for a few more years.
Can I swap an NV4500 into a truck that had an NV5600?
It can be done but it is not bolt-in. Case length, crossmember position, driveshaft lengths and shifter location all change.
What is the most common NV4500 failure?
The 5th gear retaining nut backing off, which lets 5th gear and its synchro walk off the shaft. Fix it early with an upgraded nut.
Which is better for towing?
The NV5600, for heavy highway towing, because of its torque capacity and gear spread. Either box should be kept out of overdrive when pulling heavy up grades.