You have to pull the transfer...
You have to pull the transfer case out of the vehicle. Remove the rear output yoke and drain the oil. We decided to do it in just that order. Bad idea. Drain the oil first.
Remove the speedo gear assembly....
Remove the speedo gear assembly. You will reuse this in the new tailhousing. If you have the early Dana 300 with the short shaft youll need to purchase the later assembly.
Unbolt and pry the oil pan...
Unbolt and pry the oil pan off of the transfer case. Then remove the aluminum tailshaft housing.
The front index retainer is...
The front index retainer is pulled after removing the six Allen bolts. You do not need to disassemble this component.
This is where it got tricky....
This is where it got tricky. Our bearing puller wasnt long enough (story of our lives), so we used an air hammer on the end of the shaft while a buddy held the sliding gear in place with a prybar. In a pinch, you may also be able to rap on the shaft with a soft-faced hammer while holding the gear. The puller is obviously the best method.
Heres the beef: The...
Heres the beef: The 32-spline shaft (right) dwarfs the weenie stock shaft (left).
The new housing (right) is...
The new housing (right) is made of aluminum just like the original. However, its way beefier and houses larger bearings. Its actually a modified Atlas piece.
The tailshaft comes with a...
The tailshaft comes with a new pocket bearing already installed. Pull it through the slider gear and use the included shims and bearing. Each kit is set up with the correct shims, so no measurements need to be done.
Reinstall the input retainer...
Reinstall the input retainer and seal it with a small bead of silicone.
Install the speedo snap ring,...
Install the speedo snap ring, gear (visible through speedo hole), and new tailhousing. The housing is sealed with silicone and held in place with the included Allen bolts. Miller claims Allen bolts make everything go faster; who are we to argue? Gun the yoke down to 150 lb-ft.
Make sure the assembly spins...
Make sure the assembly spins freely. If you want to use a yoke other than the nonCV 1310 yoke thats included in the kit, youll have to have it machined for proper spline engagement. The new parts are about a 1/2-inch longer than stock, so you will be able to avoid driveshaft modifications in some cases.
The original speedo gear assembly...
The original speedo gear assembly is reinstalled and adjusted.
Seal the cover, punch it back...
Seal the cover, punch it back in the Jeep, fill it with oil, and hammer down!
It seems like everything has some sort of negative ramificationTV will rot your brain, speeding will get you tickets, reading magazines other than Jp will make your hair fall out, and throttling on your Dana 300 transfer case will snap the rear output shaft.
While all of these may not be proven facts, one of them will surely ruin a good day of wheeling. The Dana 300 is surprisingly strong and has many impressive features for Jeeps running tires smaller than 39 inches. Its found in 80-86 CJs. Salvaged cases are usually snatched up quickly by those in the know. The 300s gear-driven design, mostly iron case, and multiple shifting options make it a sweet swap for CJs older than 1980. However, the smallish 1 1/8-inch-diameter 26-spline rear output shaft is often the fuse in the driveline that isnt exactly an easy trail fix.
Until now, the cure was to install an expensive Atlas transfer case or an overweight NP205. Or, you could scrounge and search for shafts at a junkyard that more than likely wont be interested in parting out a complete Dana 300. Interestingly, Dana still makes these shafts, although they arent any stronger than stock. Advance Adapters recently introduced a tailshaft upgrade for the 300 that is substantially stronger than the stock shaft assembly. The new shaft is 1 3/8 inches in diameter and sports 32 splines. The kit comes complete with bearings, a 1310 yoke, and all the parts youll need to get a real shaft in your 300. The only specialty tool required is a large bearing puller, but we found a way to remove the bearing without damage using an air hammer and a prybar. We took our case and kit to 4Wheel Parts Performance Center in San Marcos, California, to have Jay Miller make the swap. Heres what we found.