britishtrident
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| posted on 23/1/06 at 09:09 AM |
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What it all boils down to is common sense --- before fixing the sizes for anything think what is used on a production car for the same purpose.
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Syd Bridge
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| posted on 23/1/06 at 09:14 AM |
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For starters, this appears to be a classic case of a young fella not knowing his own strength, and overtightening the locknut. A very common cause of
failure in these smaller rodends, no matter what grade they are. I've seen rodends broken like this, before a car has turned a wheel.
The only bending moment is the longitudinal force exerted in the horizontal plane(or close to it) under acceleration and braking, as there are no
loads put onto the wishbone in the vertical plane. As this load is certainly no more than that in a FF, and this size joint is common in lower echelon
open wheelers, the cause of failure is more than likely man made. IE Overtightening, as has been said by many already.
Make sure that the threads in the w'bone are very tightly toleranced, to avoid movement, and use a grub screw to avoid the rodend rotating in
the 'bone.
Syd.
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NS Dev
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| posted on 23/1/06 at 09:22 AM |
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The one cause of failure that no-one has given much time to is running out of travel on the rose joint.
You say the car bottoms out before the joint runs out of movement, but presumably this was checked by winding platforms etc???
You may find, dependent on geometry of course, that you could get more movement in roll than you could get while checking vertically.
Retro RWD is the way forward...........automotive fabrication, car restoration, sheetmetal work, engine conversion
retro car restoration and tuning
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flak monkey
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| posted on 23/1/06 at 09:24 AM |
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Thanks Syd. I didnt assemble the car so cannot comment on the joint being overtightened or not. But that sounds like it could indeed be a possibility.
I am going down to the pits this morning to have a look and assess the damage and see if the car can be fixed up fairly easily.
Thanks for all the advice gents. Much appreciated, and I have learnt some things too. 
David
Sera
http://www.motosera.com
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britishtrident
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| posted on 23/1/06 at 11:56 AM |
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I have never seen 8mm (or 5/16" used for anything higher loaded than an anti-roll bar link -- and that gets pure tension/compression.
The inner pivots of the wishbone on formula ford were sometimes 3/8" UNF - Where possible UNF rod ends are preffered.
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cymtriks
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| posted on 23/1/06 at 10:30 PM |
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quote:
Originally posted by Jon Ison
Cymtriks,
If I read your post correctly i assume it applies even if like i have the joint is mounted 90* to that shown in the pics above as we are talking
failing in the lock-nut/wishbone area rather than around the eye ?
Ive never actually suffered "slop" in a rose joint but changed then regularly as a matter of course having seen what happens too nylon
type bush's, its not too late for me too go up too M16 in this position so i guess this is what you would recommend ?
always willing too learn.
If people running similar cars to yours are suffering from worn joints and you are avoiding this by changing the bearings every three races then it
might be time to change up a size.
Having said that Perhaps it's normal for bearings to weat out fast in your branch of motorsport, some cars do eat bearings though this is often
due to either a bad choice of bearing in the first place or letting dirt get in.
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cymtriks
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| posted on 23/1/06 at 10:38 PM |
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quote:
Originally posted by Syd Bridge
For starters, this appears to be a classic case of a young fella not knowing his own strength, and overtightening the locknut. A very common cause of
failure in these smaller rodends, no matter what grade they are. I've seen rodends broken like this, before a car has turned a
wheel.
I assumed that they had been fitted properly. You are right, the most common cause of failure for bearings is damage at the time of fitting.
quote:
Originally posted by Syd BridgeThe only bending moment is the longitudinal force exerted in the horizontal plane(or close to it) under
acceleration and braking, as there are no loads put onto the wishbone in the vertical plane. As this load is certainly no more than that in a FF, and
this size joint is common in lower echelon open wheelers, the cause of failure is more than likely man made. IE Overtightening, as has been said by
many already.
Hmm. Are FF wishbones designed the same way? The last time I took any interest in a FF car it had long trailing links at the rear to take the
longitudinal loads from the rear uprights.
Though vertical loads are obviously not present the lateral and longitudinal ones definitely are and my calcs were intended to give a ball park
figure.
Perhaps using lock wire instead of a lock nut would work?
quote]Originally posted by Syd BridgeMake sure that the threads in the w'bone are very tightly toleranced, to avoid movement, and use a
grub screw to avoid the rodend rotating in the 'bone.
Syd.
Or a grub screw...
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WIMMERA
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| posted on 24/1/06 at 01:50 AM |
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The best method of locking a rod end that I have seen is to machine a short split into the threaded bush and use a purpose made clamp around the
outside of the bush with a pinch bolt. It may be difficult to retro fit to an existing component.
Wimmera
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madman280
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| posted on 24/1/06 at 02:08 AM |
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I've broken rod ends in a number of different ways. Each way leaves its own clue. When they run out of angular travel they leave a dent in the
side of the housing. Breakage due to bending moments and overloading generaly shows at the end of the rod end in or near the ball housing. Sometimes
it shows a bit further down but not below the lock nut. The nut adds stability and strength to the threaded portion of the joint. Over torquing the
lock nut shows failure just where you describe it. I'm no engineer and I don't have extensive race experience, but i've made my fair
share of mistakes, I've learned a few things hopefully.
[Edited on 24/1/06 by madman280]
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Syd Bridge
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| posted on 24/1/06 at 09:24 AM |
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quote:
Originally posted by WIMMERA
The best method of locking a rod end that I have seen is to machine a short split into the threaded bush and use a purpose made clamp around the
outside of the bush with a pinch bolt. It may be difficult to retro fit to an existing component.
Wimmera
AHH, Rorty shows his head above the parapet again!!! No more nastiness, eh??
Yes, the pinchbolt is probably the best solution. Easily retrofitted if enough of the w'bone boss is protruding, though difficult to implement
elegantly in any situation. Works well though.
Syd.
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WIMMERA
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| posted on 24/1/06 at 09:49 AM |
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Think I had better nip this in the bud, I am not Rorty.
Wimmera
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Syd Bridge
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| posted on 24/1/06 at 10:22 AM |
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quote:
Originally posted by WIMMERA
Think I had better nip this in the bud, I am not Rorty.
Wimmera
Whatever you say, but the evidence points otherwise. I'll leave it at that.
Syd.
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MikeRJ
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| posted on 24/1/06 at 01:32 PM |
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quote:
Originally posted by WIMMERA
The best method of locking a rod end that I have seen is to machine a short split into the threaded bush and use a purpose made clamp around the
outside of the bush with a pinch bolt. It may be difficult to retro fit to an existing component.
Wimmera
Also putting the locking nut on the other end of the threaded bush moves the stress point caused by the lock nut to a safer location. That does mean
you need a long enough thread on the rod end/short enough threaded bush.
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