NP273 Transfer Case Drive Chain HV-064 Ford Super Duty

Replacement drive chain for the New Process NP273 chain-driven transfer case. It is the 1.50 inch wide HV-064 chain, sold as OE numbers 5003453AA, 05003453AA, 5086328AA, 05086328AA and F81Z-7A029-AA. The same chain also runs in the NP271 case, which is the wide-ratio sibling that shares the housing and sprockets.

The chain is what carries torque from the mainshaft sprocket forward to the front output shaft any time the case is in 4HI or 4LO. It is a silent-type link chain, and it stretches with miles and with dirty or overheated fluid. A stretched chain shows up as slack you can feel in the driveline: a clunk when 4WD engages or when you go on and off throttle in four wheel drive, a whine or rattle from under the cab that changes with speed rather than engine rpm, and metallic fuzz on the transfer case magnet at drain time. Left alone it eventually skips on the sprocket teeth and takes the sprockets with it, which turns a chain job into a case job.

On the bench the job is straightforward. Drain the case, pull it off the adapter, and split the two halves at the RTV seam after removing the perimeter bolts. The mainshaft, front output shaft and chain come out together as an assembly; lift them out as a unit rather than trying to pry the chain off in the case. Check both sprocket teeth for hooking or a wear ridge before you reassemble, since a new chain on worn sprockets will be noisy again quickly. Reseal the halves with RTV, torque the case bolts, and refill with the fluid the case calls for.

Fitment covers Ford Excursion and F250, F350, F450 and F550 Super Duty from 1999 up, Dodge and Ram 2500, 3500, 4500 and 5500 from 2003 up, and Chevrolet Kodiak and GMC TopKick from 2003 up. Verify the case tag before ordering, since Super Duty and Ram trucks were also built with electric shift and planetary cases that use a different chain.