ACDelco Transfer Case Synchro Hub Assembly - XHD | 2001 - 2007

What is a Transfer Case “Pump Rub” Failure?

GM transfer cases used from 1998 through early 2007 use a gear pump inside the case that is driven off the mainshaft. The pump forces oil to the planetary as well as the drive sprocket sleeve. Because the pump is driven by the shaft, the housing of the pump must "float" in the rear housing. There are tabs around the pump housing that fit into spots in the rear housing to locate the pump housing and prevent it from spinning inside the case with the mainshaft. Over time, the pump tabs can start to wear on the rear housing. GM installed a spring steel clip in the housing intended to prevent wear, but the clip can break and be rendered useless.

Since the pump housing is aluminum and is a harder material then the magnesium rear housing, it can wear a hole in the rear housing and cause a very small leak. This leak is frequently high enough on the case that it typically will not leak when vehicle is not moving and therefore not leaving any drops on the ground; it will however leak while the vehicle is in motion. Unfortunately, since the transfer case does not have a low fluid indicator the pump rub failure is often not found until there is transfer case damage from running the case out of fluid.

Avoid costly repairs to your transfer case by preventing “Pump Rub” by installing a Merchant Automotive Transfer Case Pump Upgrade kit in your transfer case today, before it happens to your vehicle.

With installation of this kit, you will have a LIMITED LIFETIME WARRANTY against pump rub. If your case ever wears a hole in the new rear housing with the upgrade installed. We will buy you a new transfer case. However, if you already have a hole in your case, we recommend installing a new rear housing for a complete repair. The MA Lifetime Warranty will only apply to installations with a new rear housing.

FAQ:

How do I know if I have an older style bushing synchronizer hub or the newer style bearing synchronizer hub?

Some early model NP261XHD and NP263XHD transfer cases used the busing style mainshaft and synchronizer hub, while all later model NP261XHD and NP263XHD transfer cases used the bearing style mainshaft and synchronizer hub. Unfortunately there is no way to verify which style was used in a transfer case without disassembling it and checking to see if the hub gear uses a bushing or bearing. If the mainshaft and hub gear use a bearing then the newer bearing style Synchronizer Hub Assembly will work. If the mainshaft and hub gear use a bushing then the mainshaft (MA #401672A) and synchro hub gear (MA #88962335) will need to be replaced to update them to the newer style bearing units.

I hear a grinding noise at low speed after reassembling my transfer case. What could that be?

A low speed grinding noise is most commonly caused by the rear output bearing snap ring not being fully seated causing the bearing to move out of proper alignment. Verify that the snap ring is fully engaged and properly seated in the rear housing and the locating groove in the bearing.

What would cause a speed sensor correlation code after reassembling the transfer case?

A speed sensor correlation code is often accompanied by a low speed grinding noise and is frequently caused by the rear output bearing snap ring not being fully seated causing the bearing to move out of proper alignment. Verify that the snap ring it fully engaged and properly seated in the rear housing and the locating groove in the bearing.

What fluid should I use in the transfer case and how much is needed?

We recommend our Performance Transfer Case Fluid for use in ALL transfer cases and have seen improved performance over the factory recommended ATF or other alternate oil recommendations. Two-quarts are required to fill the NP261HD, NP263HD, NP261XHD and NP263XHD transfer cases.

How tight do I tighten the transfer case mounting nuts for the NP261XHD and NP263XHD at the transmission output adapter?

The factory recommended torque specification is 37 ft-lbs for the transfer case adapter nuts for both the NP261XHD and NP263XHD.

How tight do I tighten the transfer case assembly bolts for the NP261XHD and NP263XHD securing the case halves together?

The factory recommended torque specification is 27 ft-lbs for the transfer case assembly bolts for both the NP261XHD and NP263XHD. 

Can my original transfer case gasket be reused if it is not ripped?

We recommend replacing the transfer case gasket any time the transfer case is removed from the transmission output adapter. It is cheap insurance against leaks that not only make a mess but could also damage your transmission!