Upper ball joint nut size

[todd1561]

Does anyone know the size of the upper ball joint nut? The one that actually holds it to the knuckle, not the 4 small ones to mount it to the control arm. I damaged mine and need to replace it, but don't need a whole new ball joint. According to this page (https://deloreantech.fandom.com/wiki/Torque_specifications) it's a 7/16-16 but that doesn't even seem to be a valid size/thread pitch, at least nothing that I can find. Oddly, this nut is also absent on the DMCH exploded parts diagrams.

Also odd is that the front end service bulletin document (SC-01-11/81) seems to suggest that both upper and lower joints use the same nut (SP10179) but on my car the lower ball joint is definitely larger than the upper.

Service Bulletin SC-04-11/81 may explain some of this. It seems to suggest that some cars have lower ball joints with a larger diameter than the uppers. I have an early car, 1561, could this explain the discrepancy?

Color me confused, can anyone shed some light on all this?

Todd

[82DMC12]

Dorman 13559 from O'Reilly Auto is a package with a few sizes of castle nuts in it. I bought that pack and it had the right size which was actually 7/16-20 in my case. I do see the shop manual says 7/16-16 but maybe that's a typo. My ball joints are Amsteer UK joints.

Note that before I bought this from O'Reilly, I went to a hardware store and bought a castle nut in the correct size and pitch, however the slots were not deep enough and I destroyed a ball joint trying to get the nut tight enough the push the pin through!!

[todd1561]

Thanks, I think it was a typo on their part. I found an old thread pitch gauge I forgot I had and determined my lowers are 1/2"-20 and uppers are 7/16"-20. This situation exactly matches the note in SC-04-11/81 where they state "on a few cars" there are lower ball joints with larger threads and it's on the dealer to locally source a matching castle nut. This probably explains why my car only has castle nuts on the uppers and not the lowers. The dealer way back when probably didn't bother to locally source the proper nuts.

So the good news is I know the thread size which was the original question, but seems like I have some kind of odd-ball lower ball joint setup. I don't currently need new lower ball joints but it seems like when I do I'll be SOL? I've only seen vendors offer 1 size lower ball joint and I imagine it's the 7/16" variety most cars have. Anyone have any idea what I might need to do short of replacing the steering knuckles one day?

Todd

[82DMC12]

Thanks, I think it was a typo on their part. I found an old thread pitch gauge I forgot I had and determined my lowers are 1/2"-20 and uppers are 7/16"-20. This situation exactly matches the note in SC-04-11/81 where they state "on a few cars" there are lower ball joints with larger threads and it's on the dealer to locally source a matching castle nut. This probably explains why my car only has castle nuts on the uppers and not the lowers. The dealer way back when probably didn't bother to locally source the proper nuts.

So the good news is I know the thread size which was the original question, but seems like I have some kind of odd-ball lower ball joint setup. I don't currently need new lower ball joints but it seems like when I do I'll be SOL? I've only seen vendors offer 1 size lower ball joint and I imagine it's the 7/16" variety most cars have. Anyone have any idea what I might need to do short of replacing the steering knuckles one day?

Todd

Interesting. I remember seeing that SC but haven't heard anyone actually deal with that problem. My guess is the LCA and the steering knuckle are the same on all cars because both ball joint variants had the same taper dimensions (just guessing!). So I bet if you replaced the lower ball joint with the "normal" 7/16-20 joint it would fit into the knuckle just fine. Never heard of alternate versions of the knuckle to deal with that issue.

[todd1561]

That would be nice and I think you may be right. Here's a side-by-side shot of my LBJ and the British reproduction by DeLoreanGO. It's hard to tell but I do think there's more of a "shoulder" on the reproduction meaning it might just be the threads that are different and the important bit, the taper, is the same.

https://toddnelson.net/misc/dmcballjointcomparison.jpg

Maybe someone who has been in this situation and replaced their LBJs with modern replacements will chime in. I did find after my last post a re-issue to SC-04 dated 1 month later in Dec-81 that goes into more detail on this situation and states it's VIN 1794-3300 that are affected by this. So quite a few cars. Although, my car, 1561, falls outside of this range. But who knows how accurate DMC records were on items like this.

[DeLoreanGo Arran]

Just to correct you above. That is NOT a British made ball joint in your photo - that is the DeLorean Europe one. The DeLorean Europe upper and lower ball joints use a metric M12 (12mm) thread. The DeLorean Go (British made) ones use 7/16-20 UNF nuts on both the lower and upper ball joints, as per the originals.

The taper on the British made ones is certainly identical to the originals.

[todd1561]

My bad, you are correct, I think I chose the picture of the Europe one because it more clearly showed the difference I was trying to highlight with my original joint. The picture of your DeLorean Go joint had the boot going up too high to really see anything.

Since you guys have probably done more research on DeLorean ball joints than anyone else do you have any input on my question above about the difference between factory LBJs noted in service bulletin SC-04-11/81? Given my car has the wider threads would I be able to drop in one of your reproduction units without issue?

[DeLoreanGo Arran]

The knuckles are all the same, as is the taper, the only difference is the threads. So yes, you'd just change the ball joint and all would be ok.