Author Topic: Designing with linkage balljoints  (Read 2204 times)

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Offline Zeyneb

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Designing with linkage balljoints
« on: May 25, 2021, 05:22:56 pm »
Hi there,

I hope you like this post. I’m considering this M8 ball joint for purchase. It is McMaster part 6275K54, they also have another one where the shank has left hand threads.

Thread Size       M8 × 1.25 mm
Center Length  36mm   
Thread Length  19mm

Ball Stud
Thread Size      M8 × 1.25 mm
Center Length  31.5mm
Length              12.5mm

I plan to buy these to redesign my car gearshift linkage system. It is a system with several rods and pivot points. See below.

Here rod item 1 is for gear selection and rod item 8 is to engage the gear. The ball item 7 and the bolt item 11 is fixed  on the subframe so all gearshift motions will translate into left-right movements of the rods item 4 and 14 which are connected to the gearbox/transaxle of my front wheel drive car.

I have removed the linkage system parts from my car to see what I’m dealing with and to take measurements on the parts. The current design has quick connect ball and sockets, I mean you can just pull them off and push them on. But this allows for dirt to get into the sockets and it is already pretty worn down.

It is common to have the rods to connect to the sockets and the levers connect to the balls right? I will maintain this aspect in my redesign with the new ball joints. So practically I need to buy 8mm rods and put some external threads on the ends with a die. I don’t think regular mild steel would last so how about 4140 chrome-moly steel? McMaster also has this in Annealed (Softened) state so it would be doable to put the external threads on it with a regular HSS die right? I understand I should harden and temper the steel afterwards to make it last. The new design would allow for some rod length adjustments. But I think it would be safe to have at least 6.2 mm of the rod threaded into the shank. As 6.2 mm is the height of a standard DIN 934 nut. I’m primarily worried how I would need to fix the rod onto the balljoint. Obviously with some kind of nut that butt up against the balljoint shank flange. But considering engine vibrations what kind of nut and retaining hardware would I need to prevent the nut from vibrating loose?

Do my considerations regarding this design make sense? Have I overlooked something where I should pay attention to? Are there some tutorials on this topic that are sufficiently specific like the actual nut that you should use for this?

Thank you for your time!

Regards, Zeyneb
« Last Edit: May 26, 2021, 12:21:39 pm by Zeyneb »
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Offline Zeyneb

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Re: Designing with linkage balljoints
« Reply #1 on: May 25, 2021, 05:32:18 pm »
Sorry but how can I get my images to show in the text?

[EDIT] It is showing fine now, with the instructions from Nominal Animal in the post below.
« Last Edit: May 26, 2021, 12:25:38 pm by Zeyneb »
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Offline Nominal Animal

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Re: Designing with linkage balljoints
« Reply #2 on: May 26, 2021, 10:08:25 am »
After posting the initial version, find out the link to the larger version of the image (right-click, then either "Copy link location" on the small version, or "Copy image location" on the large version), and then edit your original post.  Put the full URL to the image between [IMG] and [/IMG] like such:
Code: [Select]
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Offline JohnMc

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Re: Designing with linkage balljoints
« Reply #3 on: May 30, 2021, 01:20:03 am »
8mm 4140 should be fine as is. From the drawing the socket is 19mm deep I would aim to get 12mm or so of thread in there then have room for a jam nut. If you are concerned with vibration use Loctite after you have it tested. 
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