How does a cotter pin work?

[2EFNFAST]

Let's say you torque your ball joint to 80ftlbs and cotter pin it.

If you have enough vibration that causes that 80ft-lbs to be broken, won't the cotter pin quickly become useless? The vibration causes the torque to break, the nut vibrates back and forth and eventually sheers the cotter pin....no?

Obviously it works, but I just don't undertsand how that little cotter pin can possible stand up to the abuse of a nut that's already broken it's torque and trying to work itself off

[streethondas]

i never actually though bout this.... i never put the cotter pin anyways :nut:

[chkolny541]

pixie dust sprinkled on each little cotter pin, its the same dust that runs your computer

[misterrick]

Originally posted by 2EFNFAST
Let's say you torque your ball joint to 80ftlbs and cotter pin it.

If you have enough vibration that causes that 80ft-lbs to be broken, won't the cotter pin quickly become useless? The vibration causes the torque to break, the nut vibrates back and forth and eventually sheers the cotter pin....no?

Obviously it works, but I just don't undertsand how that little cotter pin can possible stand up to the abuse of a nut that's already broken it's torque and trying to work itself off


i think the only time you would have an issue is if the ball joint wasnt fully seated, came loose and was bouncing up and down in it. even then, the cotter pin is like....rotationaltorquewise.... or... something....

or possibly pixie dust

[TimeAttack]

the cotter pin doesn't take any abuse
If the castle nut is starting to un-thread due to vibration, the cotter pin will simply prevent it from un-threading past a certain point.

the cotter pin doesn't take abuse, if 80lbs of torque can be loosened by vibration, there is no way vibration can achieve the 200+ ft lbs needed to loosen the nut with a cotter pin jammed in the castle.

when it gets down to the cotter pin its as if the nut has a tack weld to the stud.

[omfgcurtis]

The only issue i could see is if a standard nut is used instead of a castle nut. The cotter pin prevents the castlenut from coming loose. There is only torque that is stopping a standard nut from coming loose.

[Rat Fink]

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[ExtraSlow]

Ratfink has that exactly right. The cotter pin isn't subjected to as much force as you think.
If it's all been properly designed, like in a cars suspension or braking system, then a team of little japanese man has already done the calculations for you. (or if you bought a chrysler, a team of moneys)
Anyway, that little pin isn't subjected to much force, but it can save you huge disasters if you don't use it. They are less than a buck from any parts store, please do use them everywhere they are called for.

[syritis]

it's also that the force isn't continuous pressure on the pin either. the vibrations will allow the nuts to loosen in microscopic amounts. so like 2 steps forward 1 step back and so the pin isn't holding the weight for very long a a time anyways. and it's not like the thread pitch is enough to cause the nut to spin itself off either. the pin it only really stopping the rotational inertia energy of the nut for almost insignificant periods of time.

[2EFNFAST]

Interesting - I hadn't thought of it like that. Thanks for the physics lesson :)

[2EFNFAST]

Whelp, just one of those days (figured I'd post this in this thread since cotter pins are related to ball joints)

http://i708.photobucket.com/albums/ww89/efnfast/bj1.jpg

I truly don't understand what happened - the ball joint is M12x1.25. OEM specs for those (locking nuts albiet) is 45-60ftlbs.

I was curious what mine was in it, so I got out my torque wrench

40ft-lbs ; check, lined up
50ftlbs; check, lined up
55ft lbs; movement, cotter pin hole not lined up
60ftlbs; movement, cotter pin hole almost lined up
65ftlbs; movm....wait, it's freely spinning. Pull it off and see the above - 3 sets of threads are totally stripped.

Balljoint is hardened steel. I fail to understand how a soft castle nut managed to completely strip 3 threads at 60ftlbs??? The last time I messed up with castle nuts/balljoints was on my cobra's tierods. I figured all balljoints were the same, and since the upper/lower LCA torque specs were 100ftlbs, so must tie rods be. At like 70ftlbs I seized the nut up on the balljoint, and when we were able to eventually get it off, threads were damaged, but not stripped to that magnitude.

:confused: :confused:

[AE92_TreunoSC]

Wrong thread's are my only answer to the balljoint ^^sometimes the ones supplied in the box arent always 100% correct, and a 1.5 will slide onto a 1.25 sometimes

I've had new threads strip on struts as well, sometimes its just the product, and there's not much you can do aside from return it.


As for the cotter pins, I've seen lots prevent wheel bearing nuts from backing completely out. usually once the preload is gone the wheel bearing lasts an hour, but the cotter pin gives enough warning sometimes to get the car checked out at a shop.

[5000Audi]

when i replace a ball joint/ tie rod, 9 times outta 10 ill use wire over a cotter pin.. not because of strength or anything but mearly makes it easyer to remove.. just simply wire snippers to em..( i run the wire through twice)

[2EFNFAST]

Originally posted by AE92_TreunoSC
Wrong thread's are my only answer to the balljoint ^^sometimes the ones supplied in the box arent always 100% correct, and a 1.5 will slide onto a 1.25 sometimes

I've had new threads strip on struts as well, sometimes its just the product, and there's not much you can do aside from return it.


That's a possibility. Sucks when stuff like this happens beyond your control.