'04 broken lower balljoint bolt, possible causes?

2004 5-lug 2.4L with V6 coils and 235/75R15 tires. Suspension is otherwise stock.

I replaced the balljoints a little over a year and 13K miles ago. Last week the rear bolt on the left lower balljoint broke off in the knuckle and fortunately it only came apart when I was backing out of a space at work and not at 60mph in traffic.

The bolt itself shows classic signs of a fatigue crack traveling across the break. It evidently started some time ago because there is oxidation darkening in progressively lighter sections. It appears that perhaps movement between the LBJ and knuckle was flexing the bolt like it wasn't tight enough. I did torque them to 116ft-lbs like the manual said.

Truck has only seen paved roads in that time and hasn't hit any major potholes or road hazards that I would think contributed. The balljoint is a cheap Quicksteer

$38 K90260 Front Left Lower Suspension Ball Joint for Toyota Tacoma

K90260 and I seem to recall they came with new bolts, but one was missing so I reused the stock ones. The factory service manual doesn't say anything about replacing them. I ordered new factory ones to go with the new LBJ anyway.

It's scary this could have caused a major crash. If anyone has insight into why this may have happened so myself and others can avoid it recurring, I'm all ears.

 

Im showing the torque for the LBJ to the spindle is only 59ft-lbs. Also, those were probably cheap bolts. I would go get grade 8 or better bolts and re torque to 59ft-lbs with some loctite. Also the lbj castle nut torque is 103ft-lbs.

 

No, the lower

What manual are you looking at? That's not what this one says:

They were factory Toyota bolts.

 

The 80 and 53 ft-lb values are pointing to the castle nuts.

What you're saying is reasonable, but that's just not what the diagram shows or at least doesn't show clearly.

 

I see, found another image that says 116 for 2WD, I've only done 4WD models.

All I can say its fatigue. Sorry to hear. Annoying when you did your homework.