I'm putting a new spindle on the car, and the two lower bolts, the bigger ones, that tie the brake backing plate to the spindle, and then the lower ball joint, call for 100 ft/lbs. unfortunately, the castle on the nut exactly covers the cotter key hole at 100. if I back it off to the previous slot, it sits at 80 ft/lbs. if I take it to the next one, it's easily 130 ft/lbs, maybe a little more.

which way should I go?

I'd try removing the castle nut and cleaning the threads on the inside as well as I could and also the bolt threads that attach to the backing plate and re-torqueing. Try tracing these with the proper tap and die to get them cleaned out. I would not go 80 ft/Ibs.

Most people do not have the proper tap and die to do that work. That is why I suggest you NEVER use a tap and a die to clean threads on both sides of an existing fastener. Many times it will lead to a sloppy fit and weaker joint.

Taps and dies both come in different fits. They are sized for different applications and classification of thread fit.

If you get taps and dies that are mismatched by a fair percentage you can get a fastener combination that is downright dangerous. With Harbor Freight junk there is no telling if the tools are even built to a recognized standard.

If the only way you have to clean a thread is with a hardware store tap and die set then only do the nut or the bolt. Never do both. At that point you need to replace one or both fasteners.

I didn't tap them, but I did clean well. not sure if that was enough. it sounds like you are saying that they are designed to align right at 100 ft/lbs?

No, they are not designed to align at 100 lb/ft. The individual parts are mass produced, not a matched set.

With 8 slots to chose from there's a pretty good chance it will align at 100 lb/ft the first time out but it isn't guaranteed.

Ball joints are machined tapers designed to lock together through a proper fit. The nut is there to pull them together properly and is left in place as added insurance. After all, they won't hold together under all circumstances.

130 lb/ft won't hurt the fastener. That size thread will take far more torque.

These are the bolts and nuts the go through the spindle and lower ball joint, not the tapered stud of the ball joint. Different thickness of the 3 parts joining together is the deal here. Make sure no dirt or grease between all mating surfaces and tighter is better with lubed threads.

OOPS.

Still, they are not matched pairs. No worries about going 130 lb/ft on those.

5/8-18 grade 5 bolts are rated for 128 lb/ft and grade 8 are rated at 180 lb/ft.

I don't recall the rating on those bolts but I can't picture them using a cheese grade bolt in there.

If they're cleaned well enough then you needn't try tracing them with a die large enough to go over your bolt. That suggestion was just meant to see if your bolt or nut was damaged because it would simply stop and bind. Try spinning your castle nut from different positions to see if it grabs early or late. It might not go much past 100 ft/ Ibs. All surfaces must be cleaned as Nantucket says.

Common nuts and bolts have single start threads. They will only start in one position.

Milk bottles, soda bottles, and things that need to move large distances with few turns use 2, 3, or 4 start threads where you can clock them and try another starting position.

Well, from what I've seen here, and from the posts that I've read, the OP doesn't really have much of a problem. If these are 5/8-18 bolts grade 5 bolts and they are truly rated for 128 ft/Ibs and 130 ft/Ibs is not too much, then torque to that value.

If not, then I've only got one other suggestion and that is to use a different castle nut on the same bolt to see if that will grab from a different position and lock in at about 100 Ft/Ibs. Bolts and nuts can be subject to stress and maybe one of the 2 has been subject to more stress than the other.

The only reason I weighed in is because I experienced the same problem with my set up going from power front drums to power front discs. I ended up resolving it by trying a different castle nut after ensuring that everything was clean and straight.

Might be overkill but you could drill another roll pin hole in the threads at that end. The nut will be further on than the hole(s) locations so integrity wont be compromised.

I personally wouldn't drill another hole. As Feets mentioned, the bolt should handle the slightly higher torque. If you didn't want to do that, other option to me would be to use a hardened washer until the nut to help line up the slot under the correct tension.

Don't over think this. On castle nuts, you go to the recommended torque and then a little more if necessary to get the pin through the hole. Never go backwards. In this case, go to 130 ft-lbs and be done.

100 ft/lbs is the minimum torque.....it's assumed that the hole won't line up so you're expected to tighten (never loosen) the nut until the hole lines up.

Of course you could always buy new grade 8 bolts and self locking nuts or use Red locktite on the nuts. 3M weatherstrip adhesive on the bolt threads will ensure they don't vibrate loose, too...but what do I know?

thanks for the replies everyone, learned a lot form this.

took the nuts off, cleaned them again, put the tiniest bit of lube on them, and switched them. first one went on the same way, hole completely covered, so just kept cranking until it was clear. second one went on and the hole was nice and open at 100 ft/lbs.

done!

That was too easy!

That's how I did mine.

You can also use a thin washer. This results in a slightly different position of the castle nut.

Ding ding ding I do believe we have a winna.