2004 Pontiac GTO Halfshaft Upgrade - Bulletproof Your Goat

In case you forget which is which, the included BMR cap is on the left and the stock cap is on the right. Failure to swap them could result in a loose half shaft as the stock units actually lock into the stub axles.

Here are two swapped assemblies: the stock unit on top, the BMR on the bottom. Notice the significant difference in shaft diameter, 131/48 inches versus 111/416 inches stock, and the heavy-duty CV boots on the BMR unit. The BMR shaft is made from 300M axle material and has a billet CV joint. These puppies won't break anytime soon!

Install the BMR halfshafts with OEM end caps in position.

Using a liberal helping of thread lock, reinstall all the OEM bolts ...

... and torque them to 75 ft-lb. If you're using new stock bolts, torque to 37 ft-lb and 68 degrees.

Apply a liberal layer of RTV to the perimeter of the Harrop differential cover. RTV with a high heat rating is always recommended. Let the RTV set a little but not too much: You want it tacky, not gooey. While you're waiting for the RTV to set up, use a razorblade or gasket scraper to remove the OEM silicone from the center-section mating surface. Make sure to clean off as much as possible for a good, leak-free seal.

Carefully hang the differential cover mount. Leave the included bolts that hold the upper mount to the body loose so you can maneuver the cover into position easily. To fit the cover onto the dowel pins and the bushings into the mounts at the same time, you may need to shim one side of the cover with a razorblade, as we did.

Using the supplied bolts, attach the Harrop cover to the center section, taking great care not to wipe or smear off the RTV during installation, and torque to 45 ft-lb. This new differential cover not only increases fluid capacity, thereby decreasing heat, it also replaces the mushy single rubber mount with two polyurethane bushings. This increase in stiffness yields a significant decrease in wheel hop for most users. Raise the differential so that the upper mount traps the bushings on the cover. Attach the cover to the upper mount using the supplied bolts.

Use an open-end wrench to slowly draw in the body-to-mount bolts. This is a tedious process that requires patience.