I just went to fixture up my spindle on the mill to drill out the tie rod taper for a 5/8" bump steer kit bolt and noticed something unexpected. The axis of the spindle shaft is a couple degrees off of being perpendicular to the tie rod knuckle hole, so if I just open up the taper the bump steer spacers/bolt will be at a slight angle and adjusting bump steer will also change toe. To me that doesn't seem right, instinctively I feel like the tie rod shaft end shaft/taper should be perpendicular to the spindle axis, and this seems like it might be a machining mistake with the original part that maybe I should fix if I'm messing with it anyway?

https://youtube.com/shorts/G5wcNZhP80c

Thoughts? Does anyone know for sure?

 

Interestingly, that angle will move the tie rod end away from the wheel, which might be beneficial WRT to fitment. I suppose I need to check with a digital level what angle that much bubble movement on that Starret level equates to, I suspect it might be less than a degree, but I found it was repeatable.

 

I suppose the side with the taper doesn't matter because it's aligned by the taper. But I would think you'd want the side with the king nut to be flat to the nut?

 

Yea, nothing seats on the tapered side, but on the top side the nut does seat against that surface... huh, but if the taper is seated it would never break if the nut isn't completely seated like it would if it were a bolt. I'll have to have a close look at the other 3 spindles I have sitting in the garage (this one I stoned the machined surfaces to make sure I had a flat machined surface to register against before I did all this measuring, so it wouldn't have witness marks of the nut not contacting all around.

Honestly, the stock assembly puts the ball joint close enough to that knuckle that even if that was a machining mistake it would only make a few thousandths difference, much less than if you space the joint away with bump steer spacers/bolt.

 

Thinking about it a little more, if I cut it so the hole was dead perpendicular to the spindle I probably should mill that surface flat and perpendicular to the hole to make sure that it does not put an additional bending force on the head of the bolt.

And I know that someone will say something like "if it was good enough stock..." well I'm putting better parts on it, making it better than stock, why not take the opportunity to machine it better also. I just need to figure out what is "correct."

 

Huh, I just noticed that in UMI's install video:

They have it clamped the same way, so they appear to be cutting the hole at a slight angle to the original one also.

 

If anyone is curious about what I ended up doing, I ended up cutting it just like I showed/like in their video, but I only opened it up to 9/16" and then used a boring bar to bore it to just a couple of thousandths over the size of the shoulder on the bolt. I shot video that I'll put up when I get the chance to catch up with that.