GM NP246
Transfer Case Chain Replacement Cost

The NP246 is the electronically controlled case GM put behind the automatics in 1998-2007 Silverado, Sierra, Tahoe, Yukon, Suburban, Avalanche, and Escalade trucks with the Autotrac system. On the dash you get 2HI, Auto 4WD, 4HI, and 4LO. Inside you get a planetary low range, a chain to the front output, a small oil pump on the rear output, and a wet clutch pack that the case uses to send torque to the front axle when it is in Auto 4WD.

That clutch pack is the reason the NP246 chain lives a harder life than the chain in a plain part-time case. In Auto 4WD the chain is loaded every time the clutch pack bites, which on a lot of these trucks is all winter long. Combine that with a pump that likes to eat its way through the rear case half and drain the fluid, and you have a case where chains stretch early and almost never fail alone.

Before you order anything, confirm you have a 246 and not a 236 or a 261/263 from a different trim. The ID tag on the rear half tells you. The NP246 problems and cost guide covers the whole case.

Chain Stretch Symptoms

• Clunk on and off the throttle. The slack in the chain gets taken up every time torque reverses. You feel it most in Auto 4WD or 4HI, pulling away from a stop or lifting off.
• Slap or rattle from under the cab. A badly stretched chain hits the inside of the case on the slack side. If you hear this, stop using 4WD until it is fixed.
• Whine that follows road speed in Auto 4WD. Changes with road speed, not engine RPM, and often goes quiet in 2HI. That points at the chain and sprockets, or bearings that ran low on fluid.
• Glitter in the fluid. Fine metallic paste on the drain plug is normal wear. Fluid that looks like metallic paint means the chain and sprockets have been grinding, or the pump is chewing the case.

Ignore it long enough and the chain jumps a sprocket or breaks and holes the case. The chain stretch guide covers telling chain noise from driveline noise.

Check the Rear Half Before You Buy Only a Chain

This is the step people skip, and why so many NP246 chain jobs come back. The oil pump sits on the rear output inside the rear case half. Over time the pump housing rubs against the aluminum case and wears a groove into it, sometimes all the way through. Fluid leaks out, the chain and clutch pack starve, and the chain stretches.

Look at the outside of the rear half around the pump area for a wet spot, a seep, or a visible worn patch. Once it is split, look at the inside where the pump housing sits. A polished ring is the start of it. A groove you can catch a fingernail in is serious. A hole means the rear half is scrap.

If the groove is shallow, the pump rub upgrade kit ($52.99) replaces the factory pump housing with an aluminum one so it stops wearing. It includes an adapter gasket, RTV, and threadlocker, but not the pump itself, so you reuse a healthy pump. If the case is worn through or close to it, buy the Dorman 917-561 rear case half ($355.99), which comes new with seals and fits the NP246 and NP261. The pump rub fix guide covers this in detail.

The Clutch Pack in Auto 4WD

While the case is apart, look at the clutch pack. Burnt friction plates, blued steels, or a smell like burnt fluid mean it has been slipping, usually from low fluid or the wrong fluid. A worn clutch pack can bind or shudder in Auto 4WD and can trigger a Service 4WD light. If the plates are cooked, do them now. The NP246 rebuild kit buyer's guide explains what the kits include.

Procedure Overview

An overview only; get the service manual for your year.

• Unplug and remove the encoder motor from the side of the case. Note its position and do not spin the shift shaft once it is off.
• Drain the fluid, then pull the front and rear driveshafts and unplug the speed sensors and wiring.
• Support the case on a jack, remove the case-to-transmission nuts, and slide it back off the output shaft.
• On the bench, remove the rear output hardware and split the case halves. Pry at the provided pry points, not on the sealing surface.
• Lift the chain and both sprockets out together.
• Inspect everything, replace parts, clean the sealing surfaces, and reassemble with fresh sealant.

The chain is the HV-072 drive chain ($110.99): 1.25 in wide, 0.375 in pitch, 49 links. It also fits the NP149, NP241 (GM), NP243, NP261, and NP263 behind GM automatics with the 5.3, 5.7, and 6.0 V8s. Count the links on your old chain before you install the new one. If the count does not match, stop and check your case tag.

What to Replace While It Is Open

• Pump rub kit or rear half. Depends on how deep the wear is, as above.
• Seals. Front and rear output seals and the input seal.
• Shift fork pads. They wear thin, and then the fork wears into the shift collar. Replace them every time.
• Sprockets. If the teeth are hooked or sharp, replace them with the chain.
• Planetary carrier. Check for chipped teeth, pinion end play, and a rough feel when you spin the pinions. A bad carrier means grinding or a noisy 4LO. The GM genuine planetary carrier 84635180 ($213.99) is the replacement.
• Encoder motor. If the truck was also throwing Service 4WD or not shifting, test the motor while it is off. The encoder motor for 2003-2007 GM ($155.99) replaces Dorman 600-910. Earlier trucks use a different motor, so match your year. See the encoder motor guide and the Service 4WD light guide.

Fill with GM Auto-Trak II transfer case fluid. GM has changed fluid part numbers more than once, so verify the spec for your year in the owner's manual or at a GM parts counter. Do not put ATF or gear oil in an Autotrac case.

NP246 Chain Job Quick Reference

DIY vs Shop vs Used vs Reman

DIY: Chain, pump rub kit, seals, pads, and fluid run roughly $200 to $300. Add the rear half and you are around $550 to $650. Add a carrier and it climbs from there. You need snap ring pliers, a seal driver, and a safe way to drop a heavy case.

Shop: Expect roughly $900 to $1,600 for a chain job with removal and install. Pin the shop down on whether the quote includes the pump rub fix. A chain job that leaves the old pump housing in place is a comeback waiting to happen.

Used: Junkyard 246s are common and run a few hundred dollars, but they are the same age as yours and many have the same pump rub and stretched chain. If you go used, split it on the bench before it goes in.

Reman: A remanufactured NP246 usually runs well over $1,000 before install. It makes sense if the planetary is chewed, the case is cracked, or you want a warranty.

Our take: if the case is not cracked and the planetary is healthy, do the chain and the pump rub fix together and you have a case that will outlast most of the truck. Chain alone on a rubbed case is money thrown away. For the full rebuild-or-replace math, read transfer case rebuild vs replace cost.

FAQ

How much does it cost to replace the chain in an NP246?

Doing it yourself, a chain plus seals, fluid, and a pump rub kit runs roughly $200-300 in parts. If the rear case half is worn through, add a new rear half and you are closer to $550-650. A shop chain job with removal and install is usually $900-1,600 depending on what they find inside.

Can I just replace the chain and not the sprockets?

You can, and plenty of people do, but inspect the sprocket teeth first. A stretched chain wears the sprocket teeth into a hooked shape, and a new chain on hooked sprockets will be noisy and stretch faster. If the teeth look sharp or uneven, replace the sprockets with the chain.

Why does the NP246 chain go bad at the same time as pump rub?

The oil pump housing rubs through the rear case half and the case loses fluid. Low fluid starves the chain, sprockets, and clutch pack. So by the time you hear the chain, the rear half is often already damaged. Inspect the rear half around the pump before you buy only a chain.

What fluid does the NP246 take?

GM specified its Auto-Trak II transfer case fluid for the NP246. GM has superseded fluid part numbers over the years, so verify the current spec for your year against the owner's manual or a GM parts counter. Do not use ATF or gear oil in an Autotrac case; the clutch pack is built around the specified fluid.