A common ancestry: Jeep U-joints
One neat thing about Jeep vehicles is that throughout the years (since 1941, to be precise), and five different parent companies, they've retained the same style 1310-series U-joint in the front and rear driveshafts. There are some exceptions to this, of course: Some early Wagoneers used a "Detroit'' joint, the Jeepster an unusually small two-piece front shaft, Grand Wagoneers a CV-joint, and the 1994-95 YJs a 1330-series yoke. While seemingly small, these 1310 U-joints are quite strong and hold up well for all uses, other than perhaps racing.
Around 1980, Jeep and Dana/Spicer (who supplied the axles) switched over to the strap-and-bolt-style yoke instead of the conventional U-bolt-style yoke. This was even used on the AMC Model 20 rearends and front output yokes on the New Venture/New Process transfer cases.
The strap type yoke (generally Spicer Part No. 2-4-6901-1X) has a bad reputation for failure, and serious Jeep owners often switch over to the seemingly stronger U-bolt-type yoke. Most Dana 30 frontends, Dana 35 rears, and Dana 44 fronts and rears use a similar 26-spline pinion shaft. The strap type yokes can be exchanged for Spicer Part No. 2-4-8091X yokes that use the full U-bolt clamping style of retention. The U-bolt kit is Part No. 2-94-28X. For AMC Model 20 rearends, the replacement Spicer part, which used a 28 spline yoke, is Part No. 2-43741. The Dana 300 transfer case's front and rear yokes, as well as the NP 207 and NV 231 front yokes, can be converted from the strap style to the U-bolt-style by using Spicer yokes (Part No. 2-4-2461X) and U-bolt kit (Part No. 2-94-28X).
Jason Bunch, owner of Tri County Gear (Dept. FW, 1143 W. Second Ave., Pomona, CA 91766, 909/623-3373) who supplied the information and part numbers, says that one really shouldn't totally condemn the strap-type yoke. Breakage usually occurs for two reasons: either the U-joint binds from excessive angularity (caused by modified suspension systems), causing an excessive load to be placed on the strap; or the U-joint itself gets worn and allows unequal loads to be put on the strap.
Jason does consider it good insurance to replace these straps (Spicer Part No. 270-18X) whenever a U-joint is changed out. If you're reusing the old bolts, a dab of blue Loctite isn't a bad idea. Torque specs are 13 to 18 pounds, just about what you can pull up to with the standard length 12-point end wrench.
On some of the strap-type yokes, Jason notes, you can drill out the threads and use a milling machine to spot-face the back side so that it'll accept the U-bolt-type hold-downs.
Jason and his crew build a lot of custom Jeeps and driveline components, and have discovered that the unusual 1994-95 Dana 35 yoke (Spicer part No. 2-4-7631-1) can actually be a good thing. It's about 5/8 inch longer in overall length and can make up the necessary needed difference in driveshaft length on some lifted Jeeps. It uses the slightly wider 1330 U-joint, but, when combined with a driveshaft that takes a 1310-series U-joint, it provides excellent clearance for high-angularity applications. A special combination joint (Spicer Part No. 5-134X) must be used. This yoke can also be drilled and milled to accept U-bolt-type hold-downs.
Most people don't grease their U-joints often enough, especially when they operate at higher angles than they were originally intended. Grease is cheep . . . but unnecessary replacement of U-joints isn't. Always put in the U-joint so that the grease fitting and the hole are in compression, not tension. I've found that U-joints without the grease hole are a bit stronger than those that are greaseable. In fact, it just may be better to use the "lubed-for-life'' style-not only are they stronger, but the seal around the bearing cap is better about keeping contaminants out.