Mark, You may want to keep a spare set of bolts around if you use them to replace roll pins. From an installation viewpoint, the bolts are much easier. From a durability standpoint, the roll pins should withstand the stresses much better. If you do use bolts, I recommend Grade 8, which you can get at Tractor Supply. Some of the hardware store bolts are ungraded or grade 2 and may not last.

I agree that graded bolts are much better than the generic hardware store items, and that spare bolts and nuts are always good to have on hand, but in this case the torque of the shaft is taken up by a spline. The roll pin is not acting like a shear pin, so only needs to restrain the u-joint axially to the stub.

Looks like your next purchase might be a gas powered pressure washer that could double as an irrigation pump!

Thank you David and Jim, your comments really help me when I'm trying to figure out these things.

I think it might be wise to get a higher grade bolt. The one I got at the hardware store is clearly cheap and low grade.

Mark,

The best bolt for this is a shoulder bolt that is slightly smaller than the hole.

The splines will carry the torque load, but the pin has to carry any loads along the axis of the shaft. That shouldn't be all that much (otherwise a spring pin would not be sufficient) but the round shoulder of the bolt is much better at carrying shear loads without deforming than the thread surface.

Chris--You noticed that layer of dirt on the ATV frame....yeah, a pressure washer would make cleaning the mud off easier, and probably have some other uses I'm not thinking of now. One thing this incident has taught me is to keep the drive section clean and maybe even reapply grease a few times a year.

Do the cross-pieces in the universal joints have a grease nipple?

If not, you can get aftermarket ones that do. Instead of disassembling the joints to lube it you than just give it a squirt with a grease gun.