|NP203 - Atlas Doubler Shift Linkage|
After stripping out the teeth on a Dana 300 transfer case, I knew that it was time to invest in the mother of all 4x4 t-cases ... the Atlas II from Advance Adapters! I chose the 3.0 gearset because of the variety of gearing options I would have with my Wagoner Machine Shop NP203 doubler. (2:1, 3:1, or 6:1 in the t-cases alone!) This made my lowest available crawl ratio right around 150:1 and my highest around 50:1. I could have gone with the 4.7 gearset, and a 240:1 crawl ratio, but wheelin' in the southeast requires wheel speed sometimes and 150:1 is more than low enough for serious crawling, IMO! However, while the NP203 doubler is AWESOME to have, it does make for some difficult shift linkage for the Atlas. Where my old D300 had plenty of space for the shift rails to go straight out from the front of the case, the Atlas II is a little larger and the shift rail for the rear output goes directly into the NP203 case. In fact, it has so little clearance that some modification is required to even get the linkage to work. The steps contained below are meant as a reference for those who encounter this problem and in no way are condoned by Advance Adapters. I am sure that some of these modifications may void certain warranties from AA. Perform at your own risk. I also have to thank Casey at WMS for his excellent customer service, suggestions and kindness in hooking me up with the right people to do this.
|First thing is first ... the rear output shift rail of the Atlas II goes directly into the body of the 203 doubler. (Assuming you have the 203 clocked upside-down.) The rail simply does not have enough room to extend all the way. Fixing this requires several things. This pic shows the thread-on ends that come with the generic shifter package included with most Atlas II transfer cases. Cut it down so that the shift rail can go all the way into it. I also grinded down the outside as far as I felt comfortable to save on the next step ...|
|Next, grind off some of the threaded portion of the rear output shift rail. I estimate that I took off about 1 cm, but the only way to tell for sure is to put the doubler adapter plate on the Atlas II and test fit several times.|
|This shows how much I took off of the rear shifter rail in comparison to the unmolested front one.|
|I used this Craftsman 1/2-20 die on the shift rail to keep the threads from getting too messed up on the tip. I would simply thread this on before I started grinding and then back it off once I was done to restore proper threads and make threading on the end fittings easy.|
|The length difference with end fittings attached. Stock front shift rail is on left, modified rear rail on the right.|
|Close up of how close the rail comes to the adapter plate at full extension. I estimate about 1/16" - 1/8" ... It's CLOSE.|
|I utilized the stock shift linkage hardware that was included with my transfer case. I was lucky enough to have a 1.75" piece of DOM tubing that ran across the middle of my cab in the perfect place, so I cut and welded a piece of the large threaded rod that came with the Atlas II to the tubing. This is where the aluminum AA shifter block bolts to at and angle to bring my levers closer to the center of the cab. If you don't have a piece of tubing running in the right place, you can either do something else or make one run there. I'm sure you can improvise. :)|
view from above in the cab.
FOLLOWUP - 8/10/03: During a recent trip to Tellico the bolt welded to the tube in this pic broke off at the weld. As a result, I would suggest finding a more sturdy way of mounting the shift block than the one shown in this pic. I will probably drill a hole through the tube and use a longer bolt that goes all the way though without a weld next time.
|The smaller threaded rods that came with my t-case were about the right length. However, since my linkage was above and behind the shift rails, they required a 90 degree bend. A short session with the oxy-acetylene torch made it an easy feat.|
|A view of how the shift sticks interact with the shift rails.|
|Another view. In the end I used only components that came with my Atlas II. It seems to work good right now. I ended up loosing my detent balls a little to make shifting easier.|