- ⅜ Ratchet
- 12mm, 14mm, 30mm Sockets
- Air Wrench
- Needle Nose Pliers
- 3/16 Diameter Pin Punch
- Snap Ring Pliers
- 6mm Allen Wrench
- Gasket Scraper
- Flat Blade Screwdriver
- Adjustable Wrench
- Permatex® Ultra Grey® Silicon
What is the difference between 21 and 23 Spline Gears?
The transfer case input gear is the gear that slides into the transmission. V6 and turbo transmission use a 23 spline gear that is slightly larger than the 21 spline gear used on 4 cylinder transmissions. On a single transfer case you must use the gear type that matches the transmission. If you are building a dual transfer case assembly, the front case input gear must match the transmission output gear. The rear case of a dual transfer case can be set up with either 21 or 23 spline gears. When purchasing a dual transfer case adapter you can choose to purchase a 21 or 23 spline version. The only difference between a 21 and 23 spline dual adapter is the coupler that connects the front and rear case. It is important to match the dual adapter and rear gear set. If your rear case is going to run the stronger 23 spline gears you must also run a 23 dual adapter coupler. If your rear case is going to use 21 spline gears, then the dual adapter coupler must also be 21 spline.
In a dual transfer case with 21 spline gears in both cases the weak spot and most common failure point is the input gear to the rear case. A dual transfer case built with 21 spline gears in the front case and 23 spline gears in the rear case is stronger and now the most likely point of failure becomes the rear output shaft. If you‘re purchasing both a dual adapter and 4.70 gears for the rear case, order both in 23 spline. There is no cost difference building with 23 spline parts if you order both the dual adapter and gears in 23 spline configurations. In these instructions we refer to different transfer case housing sections by number. The pictures below show each of the housings and its number.
1. Remove the 30mm rear output flange nut and slide the flange off the output splines.
2. Remove the speedometer sender bolt.
Transfer Case Oil:
After installing the transfer case, remove the rear fill plug and fill with 80/90W GL5 gear oil. Once oil starts leaking out of the fill hole, the transfer case is full. The transfer case oil level should be checked after 10 miles of driving and topped off as necessary. Conventional or synthetic oil may be used.
Transfer Case Oil Service Recommendations:
After any major internal work to the transfer case, we recommend that the oil be changed after the first 1,000 miles or after the first trail ride (which ever comes first) to remove debris suspended in the oil. After the initial change, the oil should be change once each year or each 10,000 miles which ever comes first. The fluid level in the case should also be checked each time the engine oil is changed. The fluid level should be checked after a roll-over as it is possible for fluid to leak out of the transfer case when the truck is on its side or is inverted.