I'm replacing the upper ball joints on my 68 Chevelle and am using a Moog K5108 upper ball joint. My chevelle had the original ball joints so I chiseled the rivet heads off and used a punch to drive the rivets out. The holes look fine and the ball joint holes lines up, but the 1/4-28 bolts supplied with the ball joint seem a little sloppy. The diameter of the holes in the new ball joint are not a tight fit to the bolt. The bolts are also a loose fit in the control arm holes. The service manual suggests drilling the holes out to 21/64 in the control arm and using a 5/16" bolt but only 1/4-28 bolts were supplied by Moog. The two inboard holes on the new joint are not round but a kind of a rounded triangular shape and are almost large enough to fit a 5/16" bolt through. The two outboard holes in the ball joint are slotted and fit tight to the bolt in one direction. I don't think I should have to drill out holes in the new ball joint. The last time I did this was 10 yrs ago so my memory is a little fuzzy but it seems like the fit of the bolts to the hole should be a little tighter. Is this OK to use as is or something to be concerned about?

I'd say if the head of a 5/16 bolt will clear the ball joint housing ,step up the holes and use 5/16 bolts .Grade 8 of course.
I'd step the holes up with a reamer that way sharp edges and stress risers are avoided thus reducing the possibility of cracks starting from the bolt holes

the 1/4 bolts should be fine. doesent the ball joint center itself in the big hole anyway? maybe not i cant remember. but if you go to bigger bolts make sure they are grade 8.

Checked the fit of the joint to the ctr hole and there is about 1/16" clearance. I guess the 1/4" bolts will be fine as they can apply a clamp load - something the original rivets can't do. But it would still be nice to have a tighter fit. Anyone else have some insight??

I just went thru this same issue on my 65 elky. I actually had 2 different size bolt holes on the 2 upper A-arms from different brand ball joints in it's history. I MIG welded the holes full and redrilled them to fit tight on the 1/4" bolts supplied with the new MOOG joints. A little surface grinding to smooth them and they are better than new.

While you are at it, check the bolt holes for the lower shock mounts. Mine were stripped in at least 1 hole per A-frame. I also welded those full and drilled and tapped them back to new. I then welded an additional 5/16 nut to the top side of the old redone nut for additional support. Just thread a throw away bolt thru the original re-tapped nut and snug the extra nut diwn and tack weld it to the old one. Turn the bolt out and run a tap thru to clean them out. These suckers will never flex or strip out now - use Grade 8 1 1/4" bolts when the new shocks go on.

Thanks for the reply. On my control arms, I'm removing the original upper ball joints. I'm the second owner of this car and its got 83k orig miles so the suspension has never been apart until now. Welding the holes up will tighten the fit in the arms but the moog ball joints have larger holes than what my A-arms have. I should probably just bolt it up and drive on down the road, but this is different than my previous experience. Apparently the clamp load from the bolt should be sufficient or the instructions would have stated to drill it out.