Thickness of tube steel for subframe connector: Grassroots Motorsports forum: Grassroots Motorsports Magazine

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March 7, 2011 11:01 a.m. Opus Dork

In my 73 Pinto, I have put a rebuilt 351 in between the fenders and definitely need to connect the front to the rear. There are no specific subframe connectors for the car that I can find and I know that the car is slowly pulling itself apart as the passenger subframe already popped several spot welds that have been temporarily corrected. I am planning on using 2x3 tube steel inserted into the front frame and welding it to the sheet metal with a connection to the front perch of the rear leaf spring.

What I need to know is that thickness of tubing should be used. Looking at other subframe connectors, they tell you a lot, but I have not found out the thickness of material to use. I have seen one person that used 1/8" plate bent into a chanel, but I want a tube as I will not have carpet on the inside and need to be fairly neat about my install.

Thank you for your input.
March 7, 2011 11:05 a.m. oldtin Dork

I used 1x3 11ga for my mgb to connect the lower link to a chassis crossmember. 11 gauge is pretty close to 1/8" tubing - and was what I had laying around.

edit - the 11 gauge is .1196 thick
March 7, 2011 11:45 a.m. unevolved Dork

I don't have any concrete advice to offer, but I must say that's a pretty awesome problem to have.
March 7, 2011 12:05 p.m. ransom New Reader

Is there any way you can tie that cage in to help with stiffening up the chassis?
March 7, 2011 12:52 p.m. orphancars Reader

Go with .120 wall tubing and you should be fine.
March 7, 2011 1:38 p.m. emodspitfire Reader

Unless you live in a really BIG Metro area, you will probably have your choice of 1 wall thickness for any given tube dimension....("any color as long as its black....)

.090" wall is probably fine if you can get it. .120" will be OK too.

Rog
March 7, 2011 2:43 p.m. wheels777 Dork

In reply to Opus:

2" x 3" x 0.083"wt is light and rigid. It will also pass tech if you finish your cage and attach the outriggers to it..
March 7, 2011 2:44 p.m. cwh SuperDork

Huntington Beach = LA. Steel supply house should be no problem.
March 7, 2011 7:26 p.m. Opus Dork

Thank you for all of the quick responses. I do live in Southern California, so no issue on finding the right size, if anything, may have too many options.

unevolved wrote:

I don't have any concrete advice to offer, but I must say that's a pretty awesome problem to have.

Puts a smile on my face daily as I drive it.

ransom wrote:

Is there any way you can tie that cage in to help with stiffening up the chassis?

Yes, that is the plan. My only hang up is that I may make the door bar removable so that I do not need to be acrobatic to get in and out of the car. As it sits, the car is more rigid with the cage, but do plan on adding steel to connect the cage to the frame to maximize strength. Not too worried about weight, the engine is at least 1/4 of the cars weight.

wheels777 wrote:

In reply to Opus:

2" x 3" x 0.083"wt is light and rigid. It will also pass tech if you finish your cage and attach the outriggers to it..

good to know. If .083 will pass tech, will 11ga or .120?
March 7, 2011 7:55 p.m. wheels777 Dork

.083"wt is the minimum.
March 7, 2011 8:21 p.m. Opus Dork

wheels777 wrote:

.083"wt is the minimum.

good to know. I will put pictures up of what I end up doing.
March 10, 2011 1:45 a.m. Opus Dork

so far, this is my plan on what to do. I will also tie in seat mounts to make sure that there is a more positive connection other than sheet metal. Last, I also have a drive shaft loop that will be installed and could be used as another cross member.

As for thickness of material to use, I am leaning toward 1/8" +/-. I will post pictures as I get it done by the end of this month. I want to get it done for the next show in the second week of April.

Thanks again for all the input so far.