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This is a clevis made for linking the tie-rods to the steering rack. This part is under dynamic loading and is getting loosened. We tried using jam nuts but it did not work well. Due to loosening the thread came out of the rack and the part fractured maybe due to bending fatigue.

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Anshuman Sinha
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  • More of the story here : https://engineering.stackexchange.com/q/18551/10902 – Solar Mike Dec 23 '17 at 22:32
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    You should look at altering the design : position of the rack or changing the position of the steering rods as the angled load will cause that thread to fail every time . The basic issue seems to be poor design. – Solar Mike Dec 23 '17 at 22:34
  • @SolarMike , yeah I knew the design was bad. But we had to deal with 2 situations then . 1. The tie rod position came from the instant axis to eliminate bump steer 2. The spring damper assembly was intersecting with the rack placement. hence we thought about making this type of clevis. Can you suggest me some way out ? – Anshuman Sinha Dec 24 '17 at 00:17
  • Move the steering rack. – GisMofx Dec 24 '17 at 00:53
  • @GisMofx I mentioned it , the dampers are at that position, which are not letting me move the steering rack rearwards. – Anshuman Sinha Dec 24 '17 at 01:06
  • Move the dampers. Their position is less sensitive – GisMofx Dec 24 '17 at 01:07
  • did you use loctite compound, or a lock nut with a nylon insert? – niels nielsen Dec 24 '17 at 06:35
  • No we did not use any such adhesive. But we used 2 nuts, working as jam nuts. – Anshuman Sinha Dec 24 '17 at 09:34
  • Loctite Corporation has a tutorial on why threaded fasteners come loose and what you need to prevent them from coming loose, you should read it ! – William Hird Dec 24 '17 at 21:40
  • is that a double ended stud? Is it a commercially made stud or did you make it from all thread or something? In any case the lock nut obviously needs to go on the threads that go into the clevis. – agentp Dec 25 '17 at 20:14

2 Answers2

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to prevent the nut from unscrewing, you must use either 1) a thread-locking compound (Loctite or equivalent) on the threads during assembly, 2) split lock washers, 3) an aircraft-grade castellated nut-and-safety-wire assembly, or 4) a nut with a nylon insert to prevent unscrewing (Nylock or equivalent).

niels nielsen
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  • Lock washers and nylon style locking nuts are no longer used in industry for applications involving cyclic forces. Proper design of the system is number 1, proper torque is number 2, with lock wire or castle nuts if required. – Tiger Guy Jan 24 '20 at 06:18
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The problem here is moments of force. Rather than stiffening the fixings, add dampers like rubber washers with steel washers either side of the rubber dampers. This should absorb much of the instantaneous moment forces while providing vibration protection from adjacent mechanisms and fixings.

The fracture is due to strain hardening of the mild steel threaded section. Really what you want is a weaker replacement section attached to the steering rack. The break occurs where the concentration of forces exceeds the elastic modulus of the bolt resulting in what happened. Ideally you want a failure to be gradual so you have warning of imminent fatiguing failure. This would be designing the bent steel section as a thinner and more flexible bit so that it absorbs much of the shock forces at motion.

Rhodie
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