NP273 Chain
Replacement Cost

The NP273 is the electric-shift version of the NP271, the part-time, chain-driven transfer case that sits behind most heavy-duty Ford Super Duty and Ram 2500/3500 trucks of the last two decades. It is a strong case. The 1.50-inch wide chain inside it is far beefier than the 1-inch chains in half-ton cases like the NP231 or NP246, and plenty of these units go 200,000 miles without being opened.

But these trucks tow, plow and idle in 4HI on job sites, and the chain is the wear item. When it stretches, it gives you a predictable set of symptoms long before it fails outright. Catch it then and the job is a chain and a reseal. Ignore it and the chain eventually slaps the case or skips teeth on the sprockets, and you are shopping for a whole transfer case instead.

What the Chain Actually Does

In 2WD the NP273 sends power straight through the mainshaft to the rear output. The chain only carries load when you engage 4HI or 4LO: the shift collar locks the drive sprocket to the mainshaft, and the chain carries that torque forward to the driven sprocket on the front output shaft. That is why most early chain symptoms only show up in four wheel drive. In 2WD the chain is mostly just spinning along.

Both the NP271 and NP273 use the same chain. The cataloged replacement is the HV-064, a 1.50-inch wide silent-type link chain sold under OE numbers including 5003453AA, 5086328AA and F81Z-7A029-AA. The same chain runs across Ford, Ram and GM medium-duty (Kodiak and TopKick) applications of this case family, which is one of the few times the aftermarket makes your life simple.

Symptoms of a Stretched NP273 Chain

• Clunk when 4WD engages, or when you go on and off throttle while in 4HI. The slack takes up all at once.
• Whine, rattle or slap from under the cab that follows road speed, not engine rpm. A chain noise does not change when you rev the engine in park.
• Metallic fuzz on the drain plug magnet or a gray, glittery tint to the fluid at service time. A little fuzz is normal; a coat of it is not.
• Excess rotational play in the front driveshaft. With the case in 4HI, engine off, rotate the front shaft by hand. A healthy case has a small amount of lash. A long chain gives you a noticeable dead spot before it takes up.
• Knock on hard acceleration in 4LO, where chain load is highest. If it ever jumps a tooth you will hear a loud bang and feel it through the floor.

Two things that get misdiagnosed as chain: a worn front driveshaft U-joint or slip spline (clunk on engagement), and a dry or failing rear output bearing (whine in all modes, including 2WD). If the noise is present in 2WD, look at bearings and fluid level first.

NP273 Chain Replacement Cost

Prices vary by region and by how rusted the truck is. On salt-belt Super Duty trucks the slow part is often the front driveshaft bolts and the adapter studs, not the case itself.

What to Replace While It Is Apart

The chain is cheap. The labor to get to it is not. Once the halves are split, these are worth doing:

• Output and input seals. Always. You already have the yokes off.
• Front output and mainshaft bearings if they feel notchy or show any spalling.
• Sprockets only if the teeth are hooked or show a wear ridge. A new chain on worn sprockets will be noisy again quickly, so look hard.
• Shift fork pads on the range and mode forks. Worn pads are the usual cause of popping out of 4LO.
• Oil pump. Inspect the pump and pickup screen; a clogged screen starves the rear of the case.

On an NP273 specifically, check the electric shift motor and its connector while the case is out. It is far easier to test and clean the motor on the bench than under the truck.

Install Notes From the Bench

• Drain the case, disconnect both driveshafts, unplug the shift motor (NP273) or disconnect the shift linkage (NP271), then support the case on a jack before pulling the adapter nuts. These cases are heavy enough that you do not want to balance one on your chest.
• Remove the perimeter bolts and split the halves at the RTV seam. Pry only at the cast pry points.
• Lift the mainshaft, front output shaft and chain out together as an assembly. Do not try to pry the chain off the sprockets inside the case.
• Reassemble the same way: loop the new chain over both sprockets and drop both shafts in together.
• Clean both sealing surfaces to bare metal, use a thin bead of RTV, and torque the case bolts in a crisscross pattern to the factory spec.
• Refill with the exact fluid on your owner's manual or the case tag. Ford and Ram do not necessarily call for the same fluid in this case family, and the wrong fluid causes shift and noise complaints of its own.

Confirm Your Case Before Ordering

Read the ID tag on the rear half of the case. NP271 and NP273 share this chain, but they are easy to confuse with other cases on the same trucks. Some Ram trucks also used the NP241DHD, older Super Duty trucks used other cases, and later model years changed suppliers. If the tag is missing or unreadable, our guide on identifying your transfer case by tag and numbers walks through it.

Still deciding whether it is the chain at all? Start with NP273 problems and cost and transfer case chain stretch symptoms. Hard parts for the rest of the drivetrain are under hard parts in our shop.

FAQ

Do the NP271 and NP273 use the same chain?

Yes. The NP273 is the electric-shift version of the NP271 and they share the housing, sprockets and the 1.50-inch HV-064 drive chain. The difference is the shift mechanism, not the chain.

How long does an NP273 chain last?

Many go well past 150,000 miles. Heavy towing, plowing, long periods in 4WD and old or wrong fluid shorten that. Changing the transfer case fluid on schedule is the cheapest chain insurance there is.

Can I replace the NP273 chain without removing the transfer case?

No. The case has to come out of the truck and be split in half. The chain comes out with the mainshaft and front output shaft as one assembly.

Is a chain noise present in 2WD?

Usually not, or only faintly. The chain carries load only in 4HI and 4LO. A whine that is just as loud in 2WD points more toward bearings or low fluid.

Should I replace the sprockets with the chain?

Only if the teeth are hooked, sharpened or show a wear ridge. Inspect them closely; a new chain on worn sprockets wears fast and stays noisy.