×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

Lock nuts vs. pinch bolts on suspension links

Lock nuts vs. pinch bolts on suspension links

Lock nuts vs. pinch bolts on suspension links

(OP)
Most race cars use turnbuckle type adjusters to lengthen/shorten the pushrods to adjust ride height. Most seem to do it using jam nuts to lock the turnbuckle following an adjustment. E.G.

http://www.chironworld.com/parts/images/uploads/100_0158.JPG

However I noticed recently that the Porsche RS Spyder uses a pinch bolt like a bicycle seat tube and no lock nut on its pushrod adjusters:

http://www.mulsannescorner.com/PorscheRSSpyderSebring2008-MF1.jpg

Just wondering what the point of the pinch bolt approach is. Does it reduce stress concentrations at the thread root where the turnbuckle enters the push rod? Or is it something more mundane like the torque applied to a lock nut altering the length adjustment slightly and therefore the pinch bolt is more precise?

Ben

RE: Lock nuts vs. pinch bolts on suspension links

I could not access your first example, but I suspect I am familiar enough with the idea...On my Mini Cooper and Lotus Cortina vintage race cars, I use both methods on various suspension bits.  I see no particular advantage, one to the other.  Each method works equally well for it's application.
Both methods (as well as others) have been used in automotive applications for over a century!

Rod

RE: Lock nuts vs. pinch bolts on suspension links

I agree with Rod that both can and have been used for suspension joints.

Jam nuts in this application are an example of a non-preloaded threaded fastener, which usually is not a preferred practice.  Having said that, they usually do not present a problem in this application.

Pinch bolts are a preloaded fastener, but they place the bolt in bending, which is not a preferred practice.

It appears that this pinch bolt design is a function of the special end fitting used on the push rod, perhaps with a "tab" on the pushrod that prevents rotation of the fitting?  Any chance to get a higher resolution/magnification image?

Your precision argument does not seem likely (jam nut deflections would be on the order of 100 µm).

Regards,

Cory

Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips Fora.

RE: Lock nuts vs. pinch bolts on suspension links

I can't access the first picture either.  But if the link is subject to sufficient torsional moments and stress, jam nuts can loosen in service.  At least one end of the link needs to have a spherical pivot, or some other means of eliminating the torsional moment should be provided.


Norm

RE: Lock nuts vs. pinch bolts on suspension links

There are two other issues I see.

1) Joint loosening. If done properly, you can make a pretty hard joint with a jam nut. Make sure there is sufficient thread engagement in the turnbuckle to avoid camming the joint loose. Pinch bolts are ALWAYS soft joints. They rely on the pinch joint not being fully closed to grab the inner metal. They will work, but may have joint loosening problems.

2) Drift in adjustment. A jam nut will not drift as much while securing the nuts. this is due to the fit between the threads of the link and the turnbuckle. Pinch joint threads are necessarily sloppy to the link to allow adjustment. As such, they sag under gravity and will change length appreciably when secured. This can wipe out your careful adjustment.

Ken

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources