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PostPosted: May 20, 2019, 10:13 am 
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I wonder if I am the only person experiencing this. My car is a book build with Ron Champion's wishbones. After a couple of years on the road (low mileage, no abuse) the 3/4" tubes are bowed or bending at the point where the shock mounting plate ends. I need to reinforce all four 3/4" tubes with 1" tube in this area. I have not seen any mention of this weakness on the site. Anybody else?


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PostPosted: May 20, 2019, 7:43 pm 
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It has been an issue for awhile. Many book cars use tube with 0.065" wall thickness and place the shock in the middle of the arm. This bending load eventually causes the arm to fail.

I would seriously consider making new arms with thicker tubing and trying to correct the loading rather than patching the existing ones.

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PostPosted: May 20, 2019, 8:17 pm 
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Thanks for the response, Andrew. There must be hundreds if not thousands of people who have experienced this. You are right, replacement is the fix.


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PostPosted: May 20, 2019, 9:22 pm 
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I kinda cheated and bought front A-arms for my build. They were made of 1" X .120 wall tubing. When I built the control arms for the IRS, I used 1" X .120 wall tubing. (Monkey see, monkey do...) So far I have not had any problems with bending of the tubing at either end. YMMV...
:cheers:

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PostPosted: May 20, 2019, 9:39 pm 
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Location: Holden, Alberta, Canada
GonzoRacer wrote:
I used 1" X .120 wall tubing

Ditto, I used 1" x .120" DOM seamless tubing from Aircraft Spruce for the lower a arms.

a.moore wrote:
I would seriously consider making new arms with thicker tubing and trying to correct the loading rather than patching the existing ones.

Good advice :cheers:

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PostPosted: May 20, 2019, 10:22 pm 
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The Champion book design is widely known for being insufficient in this area. Getting the lower shock mount relocated as close to the lower ball joint as possible is the first step to improve. This provides lower bending leverage. Moving it will change the wheel rate, so be aware. Then increase the tube diameter AND wall thickness of the lower wishbone (a.k.a. control arm, or A-arm). I used 1" x 0.083" wall with no issues.

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PostPosted: May 20, 2019, 10:30 pm 
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Joined: January 11, 2017, 11:06 pm
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I bought Jack's kit and it seems plenty sturdy. Although the car is not yet on the road, I have no concerns.


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PostPosted: May 20, 2019, 11:36 pm 
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My a-arms are 1"x0.095" and evolved into this. They originally had the book U-bracket on top of a scalloped plate (scalloped to reduce a stressor at the legs), but got moved lower as shown to provide more suspension travel.


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PostPosted: May 21, 2019, 6:49 am 
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Thanks for the input, guys. Quite a revelation, and, yes, I did find more evidence on the site. In defence of Champion's design the 3/4" tubing looks pretty, it just doesn't work.


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PostPosted: May 21, 2019, 7:34 am 
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I used 1" sq tubing for the lower control arms. The LCA tubing has .071" wall thickness. The control arm is an actual "A" with the cross brace under the shock mounting area and the top plate incorporates a fish mouth. This design was stress tested :oops: i.e. pot hole big enough to bend the aluminum tie rod adjuster. The tie rod adjuster(s) were replaced with steel adjusters but the arms are OK. Yupper the shock mount is real close to the BJ. Davew


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PostPosted: May 21, 2019, 7:43 am 
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Joined: April 1, 2010, 10:26 am
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I snapped a lower control arm at a track day. So I swapped to a Jack setup, very impressed, Very easy to build, strong and fully adjustable.

http://www.kineticvehicles.com/ControlArms.html

Graham


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PostPosted: May 22, 2019, 2:51 pm 
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Thanks for the input, guys. This was quite a revelation to me. In defence of Champion's design, the 3/4" tubing looks pretty, it just doesn't work. I am currently building another wishbone jig.


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PostPosted: May 22, 2019, 9:11 pm 
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Location: BC, Canada. eh?
This is what I did. The tubes are DOM, and the plate on top, where the shock bracket is welded on, is 3/16" plate, You can see that the plate was heated & curved, so it wraps around, down between the legs of the arm. The plate was seam welded to the DOM all the way around, including underneath.

I think it's pretty strong...

**I've since replaced the upper A arms with built-up ones that give more adjustability.

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lower a arm small2.jpg [ 204.36 KiB | Viewed 1409 times ]


I had them powder coated after fabrication was complete.

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PostPosted: May 23, 2019, 1:26 am 
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zetec7 wrote:
I had them powder coated after fabrication was complete.


Now you're just making me jealous :lol:

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PostPosted: May 23, 2019, 1:01 pm 
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Location: BC, Canada. eh?
LOL! Strangely, unlike virtually everything else around these parts, powder coating is still cheaper than painting on items like this.

I still have some reservations about powder coat, though. If you're in a wet place like me (Pacific northwest), the tiniest pore in the powder coat can lead to massive rust under the coating, without any sign of it from the outside. I've seen some horrific examples....

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