2004 Pontiac GTO Halfshaft Upgrade - Bulletproof Your Goat

Here is the completed cover, stub axles, and halfshafts. Refill the center section with fluid and friction modifier. You'll need three bottles of SAE 75W-140 GL-5 Synthetic Gear Oil (GM PN 89021809). The new Harrop setup takes just under 3 liters and requires the addition of one and a half ounces of GTO-specific friction modifier (GM PN 89021958).

For those with an aftermarket exhaust, note that this work was done at Stainless Works while prototyping an after-cat system. Our BMR carbon-fiber driveshaft doesn't clear the stock exhaust, so keep this in mind. This beautiful piece of craftsmanship is rated to well over 800 hp and carries a critical speed of over 8,000 rpm. Each BMR driveshaft comes with a cryogenically frozen front yoke and a custom-machined 300M billet pinion-yoke adaptor for maximum durability.

Installing the BMR driveshaft is simple. Unbolt and take out the stock driveshaft. Using an impact gun, remove the stock pinion yoke adapter, and replace it with the BMR billet piece. Torque the pinion-yoke adapter nut to 120 ft-lb.

Unbolt the upper center-section mounts, and install the included spacers to move the driveshaft down to clear the floorpan as shown. You may need to trim one of the rear seatbelt bolts that protrudes into the driveshaft tunnel, but on our particular GTO, it wasn't necessary.

If your GTO has a Harrop rear differential cover as ours does, remove the upper differential-to-frame mount, and install a spacer like this one made for us at a moments notice by Stainless Works. Since this was the first time anyone had done this combination, no one knew to expect this. BMR now stocks these spacers. Double-check all the changed bolts, and check for differential fluid leaks. If everything is up to snuff, take your Goat for a ride!

Slip the front driveshaft yoke into the transmission, and secure the rear driveshaft-mounting flange to the rear pinion-yoke flange using the included nuts and bolts. Double-check the suspension clearances to make sure the driveshaft won't hit anything.