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v7guy
03-19-2008, 05:05 AM
I have some tubular lower A arms that are apparently not up to the task of being structurally sound.

So I'm faced with reinforcing them and replacing a bent shock mount. Is 1/8" (11ga) 1018 steel thick enough to provide the needed strength?

The rough idea is to add gussets to the spring perch and to where the spring perch mounts to the tubes. Then to also put a solid plate across the middle triangle. If there are better/lighter ways to do it I'm all ears.

these would be the arms
http://www.bmrfabrication.com/A-arms/hi-resLower.jpg

I've got another threaded tube end to make both tubes rod ended.
the weakest point seems to be the rectangular shock mount where it began to bend across the bolt holes.

v7guy
03-19-2008, 02:23 PM
Do I need more pictures or a better description to get some suggestions?

Apogee
03-19-2008, 04:06 PM
Do you have pics of the failure?

Normally, 11 ga can be made plenty rigid with the proper geometry, gussets, etc, but that's assuming that you're not topping and/or bottoming out against the shock mounts excessively...that's what bumpers are for if I'm not mistaken. I agree with you though that the weakest point is definitely through the two mounting holes.

Tobin
KORE3

v7guy
03-19-2008, 05:55 PM
https://static1.pt-content.com/images/pt/2008/03/PC170017-1.jpg
https://static1.pt-content.com/images/pt/2008/03/PC170018-1.jpg
https://static1.pt-content.com/images/pt/2008/03/PC170029-1.jpg
https://static1.pt-content.com/images/pt/2008/03/P6180011-1.jpg

the shock definitely has more travel, 3 inches or better, it's not been bottomed out. I have a rubber washer on the shock shaft to watch the compression.

I've considered several different approaches to strengthening this thing including running another tube from the bend in the back tube to the front tube/cross tube intersection to brace it and then attaching the shock mount to it. I've considered gussets at all tube intersections and at the edges of the shock mount. I've also considered just doing the aforementioned plate. I don't want to just reinforce the shock mount and then find another weak spot that ends in catastrophe, but i'd like to keep it from being really heavy too. I'm open to all suggestions.

KWIKND
03-19-2008, 06:57 PM
The horizontal span is too long for the thickness of the material. I think by adding (2) 1/4" rectangular flat washers with hole drilled between the coilover cross bar and the LCA the loads should transfer nicely to the vertical legs of the weldments. And the bolts look to be long enough also for the added thickness.

Dan

MrQuick
03-19-2008, 10:07 PM
I agree.....Just wondering but was that LCA built for coil overs?

Another thought would be to send the arms back for replacement or repair. Fixing it yourself might open up a big liability can of poop.

v7guy
03-20-2008, 12:11 AM
I emailed the company and they told me to bend it back and then sent me some 1/2 inch thick aluminum pieces to put between the shock and the mount.
This may work, but the car does see some pretty good corners and I'm concearned with that solution being adequate.
As far as liability goes, if they fail I'm not sure it'll matter.

John Wright
03-20-2008, 07:14 AM
adding (2) 1/4" rectangular flat washers with hole drilled between the coilover cross bar and the LCA the loads should transfer nicely to the vertical legs of the weldments. And the bolts look to be long enough also for the added thickness.

Dan

Could also box the ends of the shock bracket by plating each end, you may loose access to the bolt head if you do this though....

Apogee
03-21-2008, 09:17 AM
I think I'd beat it back into shape and then weld flat strips of 1/8" or 3/16" sheet metal underneath the holes, one for each side. You could then fashion up some horseshoe shaped gussets to box in the ends of the shock mount and still access the fasteners.

That shock mount looks a lot stouter in their website photo...seeing it from underneath makes it fairly obvious why it bent. I'm guessing you run fairly stiff springs and valving in your shocks, but if you know what it they are, it could be informative.

Tobin
KORE3