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Tubular control arm issues

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Tubular control arm issues

Post by DrJ on Sun Apr 10, 2016 8:42 am

To anyone in the group who has done this:

Just in the finishing stages of the rear conversion so I began to study the front end. What I noticed was an interference issue with the drivers side lower control arm and the outer most rack and pinion mounting flange. A rough measurement seems to show 3/4" distance between the center of the existing LCA bolt and the side of the R&P flange. When I hold up the new tubular arm there will be about 1/16"-1/8" of interference. So the options look to be either grind off some metal from the R&P flange (it's a round flange hitting a round LCA eye so a little grinding should go a long way) or recruit the "other" R&P mount flange. My unit has 3, one on the passengers side and two on the driver side either side of the R&P mechanism. The original builder used the outer most flange. There may be an issue using the other flange as the cross member may not be reinforced at that station, have to look.

Figure someone must have run into this as well on their conversion. Any ideas??

DrJ

Posts : 131
Join date : 2014-06-19

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Arm Resolution

Post by DrJ on Fri Apr 15, 2016 8:20 am

So I am answering my own question. When the front suspension was completely dissembled and I could hold the new LCA in place I discovered horizontal interference with the rack mount to be only 1/16" but now realized vertical interference of about 1/8" with the rack-tie rod interface. What I learned with steering geometry is that shifting a rack vertically will generate bump steer. Lines drawn thru both the UCA and LCR will intersect at a point inboard, what is known as an instant center. A line drawn thru the tie rod should intersect that point. Shifting the rack vertically changes the plane of the tie rod so that it doesn't.

You can shim the rack foward off the cross member within reason, without causing geometry issues. I needed 5/16" to clear my vertical issue. Shimming out will likely change the toe adjustment so that needs correction. To solve the horizontal issue I pulled the rack off the car and carefully grinded 3/32" off the drivers side mount flange. The flange is 1/4" thick so no worries there. Now the new LCR is good to go and I had the opportunity to sand, prime and paint the rack and cross member to boot.

DrJ

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Join date : 2014-06-19

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Re: Tubular control arm issues

Post by David V. on Fri Apr 15, 2016 2:57 pm

I'm having trouble visualising your issue. To be honest I am not that versed in suspension troubles. I'll take a look on my own car in a few weeks. Thanks for the info all the same!

David
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David V.
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Lower control arm

Post by DrJ on Sat Apr 16, 2016 8:21 am

Well David you and others may not have this problem. Hotrod and I talk a bit and his cross member is drilled differently form mine. As I understand it the standard spacing for the Mustang II rack mount is 16" on center, which agrees with mine. Standard spacing of the LCA pivot points is 22 1/4", mine measures out at 20 3/8" hence the horizontal interference issue. The center of the drivers side LCA bolt was only 3/4" from the side of the rack mount. The diameter of the new tubular LCA is 1 5/8" so I needed 13/16" just to touch the mount. The vertical issue, I would assume would affect everyone, but the cures to both ended up fairly easy. Just wanted to post the ordeal in that it might prove helpful to someone in the future.

I should take the time to post my own build thread.

DrJ

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