Quality Time With the Transfer Case
In the last installment (June ’11), we tapped ATS Diesel Performance with a rebuild of our Ram’s slipping slushbox. While we were in rebuild mode, and the T-case was out of the truck, we decided that we’d go through that vital drivetrain component as well. We expected the 175,000-plus-mile NP241 to be in the same sad shape as the rest of the truck. However, once we got through the ½ inch of 17 years of accumulated road grime and cracked into the T-case, we found a much different story.
The old fogeys at the off-road rags of days gone by were quick to denounce the chain-driven and aluminum-cased gear splitters when they started popping up in the early to mid-’80s. And, truth be told, those first boxes weren’t the best examples of a T-case out there. However, by the time the NP231 and NP241 rolled around, the chain-driven cases had come into their own. Of course, the fuddy-duddies were still on about cast iron and gear drives. They said things like, “The cast-iron case can take the occasional rock hit and is much stronger than the thin aluminum cases.” We wonder if they’ve ever heard of skidplates. They said things like, “The direct gear drive is a much stronger method of transferring power to the front axle than any chain.” We’ve not seen a lot of chains that just went pop.
The fact of the matter is, the newer T-cases are reliable and have fewer moving parts than their heavy gear-driven predecessors. That means you don’t need three hands when rebuilding them, and just about anyone who can do a brake job (especially drum brakes) can do it. In our case, we were all set up for a full-on rebuild, but once we opened the case up, we found the chain was in great shape with no noticeable stretch or wear, as were all of the vital internal parts. We wonder if the previous owner ever even used four-wheel drive.
As much as we like the chain-driven cases, we just can’t abide by the slip-yoke tailhousings. If your rear driveshaft goes, there is only so far that a spray-can cap and duct tape can take you. Once we were inside the case and everything was in good shape, our rebuild became a simple slip-yoke eliminator conversion. So, we contacted JB Conversions for a heavy-duty 32-spline slip-yoke eliminator kit and shot some pictures as we went along. Normally, when you do a slip-yoke conversion, you will need to either order a new driveshaft or modify your existing one. We have some things in the works for the rear axle, and we’ll be adding some lift in the next installment so we are holding off on the driveshaft until we are done with that stuff. By eliminating the Achilles’ heel of the slip-yoke tailshaft, we hope to see another 175,000 miles of trouble-free service.
This first step is actually easier to do if the T-case is still bolted to the transmission. While the directions don’t say it, pull the front yoke or driveshaft flange off before cracking the case open. It will save you trouble down the road.
You are going to want a decent pair of duckbill-type snap-ring pliers if you are doing this at home. The pin-style pliers just won’t work, and there are enough snap rings that need to be removed and reinstalled that a pair of regular pliers just isn’t worth it. Don’t force anything—if a part doesn’t want to come off, look for the snap-ring holding it on. This is right inside the factory slip-yoke tailshaft.
The speedometer drive gear is made out of plastic and rides on the mainshaft between two snap-rings. Pay attention to where it rides as there are two sets of grooves that you can reinstall it on the aftermarket shaft. Only one location is correct.
Once the speedometer drive gear is out of the way, pull the eight bolts holding the case halves together. There are two cast-in pry locations in the case. One is in the lower right corner, and one is in the upper left corner (if you were looking at the case as it sits in the truck from the rear). Pry in these locations and it should come apart. If it doesn’t, use great care prying in other spots. You don’t want to damage the sealing surface.
This little washer could make life interesting if we were doing this job in the truck. This is the shift fork spring, and the washer prevents the hardened steel spring from scoring the aluminum of the T-case, so it isn’t something you can just throw away.
Once you’ve got the case open, remove the mainshaft, chain, and front output all at one time. Keep the chain parallel to the case and it should all slide right out.
The earlier New Process chain-driven cases have two sets of needle bearings lightly pressed into the main gear on the mainshaft. Later on down the road, the company figured out that the added moving parts weren’t really necessary and stopped using them. The JB Conversions mainshaft doesn’t use them either, and they need to be removed from the gear. We didn’t have a piece of solid stock with the proper outer diameter, but since it was a light press fit, we had no problem using a 1½-inch x ½-inch drive socket. They can also be carefully driven out with a brass drift.
In addition to reducing moving parts, the elimination of the captured needle bearings resulted in the ability to bump the diameter of the shaft up at the gear. Also note the size increase of the 32-spline output over the factory part. The size increases make for a much stronger mainshaft.
Before putting the case back together, make sure that the plastic shift fork bushings are present and in good shape. If yours are hashed or missing, take the time to order new ones. JB Conversions stocks them for some applications, but we’ve also had good luck with Rock Auto for these parts. The shift ring rides on these and they prevent wear of the ring.
When you pull the gear off the mainshaft, pay attention to the orientation of the gear. It’s a 50-50 shot that you’ll get it back on the right way, but this isn’t something you want to leave to chance. The JB Conversions kit comes with all new snap rings for whatever ones we had to remove. Make sure that new rings are fully seated in the grooves.
Clean the mating surfaces of both case halves. These cases have no gaskets for sealing—they rely on RTV, and as such, clean mating surfaces are important. Since we were able to pry our case open using the cast-in recesses, we were able to use a Scotch Brite pad to get the job done. If you have a harder time separating the case halves, you might have to use a file to get the aluminum flat again before cleaning off the old silicone.
The oil pump is driven by the mainshaft and vital to the case’s operation. We always clean the oil pickup when we’ve got one of these open. The pickup tube just slides into the pump and is sealed with an O-ring. Make sure the tube is in the pump and the O-ring is present before sealing the case up. Splash-oiling alone won’t keep these things alive.
We went with the basic kit that reuses the front part of the factory tailhousing. We have plenty of rear driveshaft length, and our ’94 still uses a speedometer gear, rather than a tone ring for the speedometer signal, so we saved some coin by going with the basic kit. Regardless of which kit you choose, there are four ears on the oil pump that index into the tailshaft housing. Make sure they are aligned, and don’t force the tailshaft housing into the case.
We’ve seen a bunch of these cases that were missing this magnet. The magnet collects any ferrous debris floating around in the case, keeping it away from the moving parts. Steal one off the fridge if yours is missing. Clean it before reinstallation. We’ve found it helpful to put a dollop of silicone on the magnet so it stays in place while reassembling the T-case.
All of the bolts that hold our case together are dry bolts. That is, they don’t have any oil behind them, so it isn’t necessary to apply silicone around the holes. We use Permatex’s Right Stuff for a leak- and worry-free seal. A 1⁄8-inch bead is plenty if your sealing surfaces are in good shape. Too much silicone can work its way into the case and gum things up.
After replacing the tailshaft bearing with the new included one, the new tailshaft retainer needs to be installed. Before installation, grease the seal and the outside of the new yoke. Failure to do so can lead to premature seal failure.
Even though the kit includes new rubber star washers to seal the yokes, we like to put a little bit of Right Stuff on the splines of the yokes to be doubly sure that no ATF can get through.