Well, you ruined that housing-you can't weld cast to mild steel." Jay Prosche-Jensen of Ultimate Driveline has heard that from "experts" for 30 years. Being the mild-mannered guy he is, his reply is always the same: "That's what everyone keeps saying, but I've never had one fail, and I've built thousands of rearends this way."
If you've spent any time around dirt and Danas, 12-bolts, or Ford 8.8s, you've learned these housings can be weak where the tubes press into the cast center. Over time it's common for the plug welds that hold those tubes in place to fail. At the very least, they'll leak after flexing from trail use, high mileage, or abuse on the street. At worst, they'll outright fail and leave you stranded, as our Dana 44 did.
1. Most axletubes are pressed...
1. Most axletubes are pressed into cast centers and secured with a few plug welds. This Dana 44 had six plug welds around each tube, and all were cracked, resulting in 1/16 inch of play where the tube pressed into the center and a whopping 5/16 inch of runout at the wheel bearing. This eventually destroyed the axle splines, spider gears, and internals in the posi, and spun the carrier bearing, which junked the housing.
The ultimate fix is to fully weld the tubes to the center housing, but there's some mystery and myth surrounding the process. The problem is welding dissimilar metals; it's not so much their alloy composition as the difference in cooling rates. "When it isn't done right, you'll hear a loud tink! as each weld breaks loose when it's cooling," Prosch-Jensen told us. Since the cast steel housing cools slower than the mild steel tubes, the weld pulls away from one side of the joint.
The accepted solution is to bring the whole assembly up to a given temperature in an oven, make the weld, and then control the cooling rate to keep the weld from pulling away. Prosch-Jensen doesn't have an oven, but he does have a secret weapon. He found a particular MIG wire that allows the molecules to keep "flowing" as the weld cools, allowing the weld to stretch and give. The result is a strong weld with no tink! If you're handy with a MIG, you might be able to do it yourself, though the Esab high-silicon wire is expensive.
Prosch-Jensen custom-builds extreme-duty rearends week in and week out, and still takes the time to swap the spool of wire just for welding tubes to cast housings. You also need to be spectacular at controlling heat buildup and penetration, otherwise you'll warp the housing. Prosch-Jensen built a custom Dana 44 for us, and he's like a machine: When we got the housing back, the axles slid home perfectly. With fresh plug welds, extra-thick-wall tubing, and a full radius weld, this housing is up to whatever abuse we'll give it.
 2. Our trashed rearend was...  2. Our trashed rearend was an extreme case-they don't usually fail so completely. But Jay Prosch-Jensen at Ultimate Driveline said it's not at uncommon for axletubes to come loose and rotate in the housing or pull out. At best, you'll end up with a persistent leak at the tube. At worst, you're walking off the trail. |  3. As with any welding project,...  3. As with any welding project, success depends on the prep. Prosch-Jensen uses a torch to burn out any grease and oil from between the tube and the cast housing, ensuring there's nothing in there to contaminate the weld. |  4. After the grease is thoroughly...  4. After the grease is thoroughly burned out of the joint (and there was a lot of grease), the metal is ground down to get a good, clean surface to weld. Use a sanding disc, not a grinder, as you just want to remove surface rust, not dig down into the tube and make a thin spot. |
 5. The plug welds need to...  5. The plug welds need to be ground away with a carbide tip before being welded. Supposedly the factory brings the housing up to temp in an oven to make these plug welds, but Prosch-Jensen says they're almost always cracked. He has seen rearends come from the factory with a bead of silicone around the seam to fix a leaking joint. |  6. Prosch-Jensen demonstrated...  6. Prosch-Jensen demonstrated by custom-building a replacement Dana 44 with extra-thick-wall axletubes, starting with a bare casting. Our truck is fairly light duty, so we went with the 44 rather than the Dana 60s he usually builds. |  7. Here's our original, reinforced...  7. Here's our original, reinforced housing in bare metal. The plug welds are perfect. Prosch-Jensen filled in the big housing spreader bosses (used by the factory to install the differential) and completely welded the tube to the housings. The MIG wire he uses is an Esab high-silicon wire, which keeps a median temperature between the different cooling rates of cast and mild steel. Without the special (and extremely expensive) wire, the welds would pull away from one side of the joint and do absolutely no good. |