Getting a Thicker Shaft – Swapping an Atlas Transfer Case Input Shaft

I’ve been working with Advance Adapters on a project for quite some time now and we’re getting ready to wrap things up. After many test fits with an empty mock up Atlas transfer case, it was time to order in the real deal. When it came in, I discovered a minor mixup, the input needed on this transfer case is a 31 spline but instead it was shipped with the common 23 spline input which is used on the vast majarity of Advanced Adapters’ transfer case adapters.

Instead of shipping the transfer case back to Advance Adapters, I decided to replace the input shaft myself, replacing the input myself both saved time from not having to wait on shiping both ways and gave me the opporitunity to write a “how-to” which will hopefully help someone out in the future.

Advance Adapters sent the 31 spline input ring assembly with the bearing and seal installed already. This eliminated the need to press out the input bearing and replacing it along with the input seal. Before the 31 spline input goes in, we obviously need to take out the 23 spline input.

The first thing we need to do is to get the Atlas on a work bench and flip it upside down without damaging the breather. You can either remove it or put the Atlas on a block so it doesn’t sit on the breather. You will see the the inspection cover being held on by 14 bolts. Remove these and remove the inspection cover by utilizing the pry points on each end.

Once the inspection cover is removed, you will need to remove both the front and rear cluster pin bolts then push the cluster pin out from the front while holding the cluster gear with one hand. Lift the cluster gear from the case being carefull to not let the needle bearings fall out from inside the cluster gear. Once the cluster gear is set aside, remove the two thrust washers.

Once the thrust washers are set aside, remove the 6 bolts holding the input ring to the Atlas housing and remove the input ring assembly. Remove the drive gear from the input assembly by first removing the snap ring then the drive gear. Advance Adapters says this is a light press fit, but sometimes it can be pulled off by hand. Install the drive gear onto the 31 spline input assembly and make sure the snap ring is seated in correctly.

Slide the input ring assembly into the Atlas transfer case housing while lining up the notches in the synchro. Then line up the 6 bolt holes on the input ring with the 6 bolt holes on the Atlas housing. Make sure the rubber seal is properly seated on the input ring assembly before tightening the input ring assembly against the Atlas housing.

After tightening the 6 input ring bolts, put the thrust washers back into place on both sides of the Atlas housing and lower the cluster gear back into place. You may need to rotate the input to get the gears to mesh properly allowing the cluster gear to be lined up with the cluster pin hole. Push the cluster pin back through the rear of the Atlas. Just before it’s in all the way, put a new o-ring on the cluster pin and push the cluster pin the rest of the way through the cluster gear and out the front of the Atlas housing far enough to install a new front o-ring on the cluster pin. Center the cluster pin in the Atlas transfer case housing and install the cluster pin bolts.

Before installing the inspection cover, scrape off any old gasket material that is stuck to the Atlas transfer case housing. Install the inspection cover with a new pan gasket securing it in place with the 14 inspection cover bolts.

Once you install the inspection cover, you’re ready to do it on the rocks! If you have any questions please feel free to shoot me an e-mail but i do recomend using the Atlas transfer case installation guide as your primary reference for doing work to your Atlas transfer case.

See you on the trail!