I am finishing up replacing the mopar OEM flex? joint with two Flaming river U joints, when I switched from PS to manual. The issue is, the shaft is .75", the billet u joint outer diameter at the shaft, is approx 1.125". I joined the two with, at this time, a 5/16" allen shoulder bolt. Its a nice snug fit. The shoulder bolt has a 1/4-20 male thread. Do I want the 1/4-20 to try and compress the billet u joint further for an even tighter fit? Personally I don't think it would do a lot of compression, if any, being its small size, and robustness of the u joint. Or just tighten a 1/4-20 lock nut against the shoulder, and let it float? However if it ever develops any play, it will only increase over time. Play on the steering is not my goal. Welding is not an option. Other then that, I am happy with the end result.

If the shoulder bolt does not go through a indent on the shaft you risk the shaft/joint coming apart. You won't get much clamping force from a 1/4" bolt , I don't think a shoulder bolt is a quality bolt for strength. Might look at pinning the shaft / joint to keep it from coming off. This is not just something that you just say yah, that'll work.

There's a roll pin that goes through the coupler and steering shaft. If it fits correctly use it.

Yes, I thought that was to be my solution, but the pin hole in the one u joint already drilled I had on the shelf, and the oem pin, both measured an odd to me, diameter like .334"? reproducing that hole in the shortened shaft was an issue, so I went the 5/16" bolt route. Thanks

So you drilled out the pin hole to the larger 5/16" shoulder bolt? thats OK . Now the steering shaft has splines that the bolt goes through? if so you should be good to go. If not the hollow shaft will shear the bolt off from the back and forth movement, I have seen it happen, totaled the car.

are you using a hardened "stripper" bolt ? that is one with a allen hex round end about 1/4" thick, the shoulder [which in this case is 5/16" diameter], and 1/4x20 threads on the end. if using this in the .334dia. pin hole, that is too sloppy of a fit. even if it feels pretty good, there is too much play there, allowing for back and forth movement which will probably/eventually lead to a failure at some point. the .334 diameter of the pin is because it is intended to be driven into a smaller hole, and because it is a split pin [it is, isn't it ?] it will take out all movement. i also believe the pin is made of a kind of spring steel. of what grade, i can't say.

Let me clarify a few points. My OEM shaft is solid 3/4", to add the pair of U joints, I shortened the shaft 2+", this removed the OEM .334" dia solid pressed pin, I drilled a new 5/16"hole
thru the new u joint and the now shortened shaft, and used as you mentioned, what seems to be a precision ground and hardened "stripper bolt". The fit appears as tight as possible, and still be removeable by hand. The but part is, will this connection be enhanced by trying to use the 1/4-20 threads to clamp the universal joint further/tighter, or just use the 1/4-20 as a retainer, with no compression?

And as also noted above, I also have personal experience with off road excursions at 60+mph, in a rental RV, with my family on board, caused by complete steering separation. Nobody got hurt. I am not cutting corners.

if the coupler pic by cudajohn is what you are using, you won't be able to do anything more with a through bolt except use as a retainer. the 1/4x20 threads will be strong enough for this retention, but unless the coupler is slotted, no more tightening of the shaft is possible. and in order for a slotted joint to be able to be tightened further, the clamp bolt can not be centered in the shaft. think your basic tie rod adjuster sleeve. when clamped [uniformly], the clamping bolt, or pinch bolt, will be off to one side. that allows the split to clamp as tight as possible on the shaft, be it threaded or not. the bolt you have and the way you used it should work.

Pics:
1st is the overall setup, shoulder bolt circled
Second is closeup
Third is with a spacer washer, that is the issue, do I tighten against the shoulder bolt and let it float or against the u joint?
Forth is a bolted solution, nylon locking nut to soon be replace with all metal "stover" locking nut.

PS, for those concerned, all u joint set screws are screwed into machined divots.

i see now. you don't want that to float back and forth. i would do this. #1, get a bolt 1/4"ish or so shorter so the shoulder is just a tic shorter than the joint. then tighten nut to spec. or, #2, get a spacer that will take up the area the shoulder sticks out of the joint. if going that route, i would like to see the one side of the spacer contoured to the joint. tighten nut. either way, tighten the nut so the bolt doesn't move. machined divots for other screws is good. add a drop or two of blue loctite also. those screws are known to loosen up at times.

That's all good sound advice and should be end of the project. I did not mention, I spot faced both sides of the drilled hole on the U joint, and will go the spacer route. Thanks

the spot face was one thing i forgot to mention when using just a nut and bolt face. that prevents a localized stress point on the bolt head and nut. my mistake, and i apologize to any others for omitting that crucial step.