Installing Sub Frame Connectors

So I am getting some great ideas for putting SFC in the T Bird.

Now, what is the best way to set up the car for putting them in? I have heard you should have the car on it's wheels/on a frame rack/on jack stands, etc, etc.

These will be thru-the-floor ones so the floor will be cut up for the install.

Thanks,

Bill

I always put the car and stands and leveled it up. Not sure how much it helps but it dont hurt none.

richter69 wrote:I always put the car and stands and leveled it up. Not sure how much it helps but it dont hurt none.

Thanks Jon, where do you place the stands? It seems when I put the front ones under the jacking points at the front of the rockers the doors get hard to open!! I guess the SFC's will help that!!

Bill

Yea, level & square the car on the jack stands. No reason to "build" any unwanted diagonal twist into the body/chassis by mistake because the car wasn't sitting level on the stands. Once you get it to what you think is square/level on the stands, walk around the car & check all the fender/door/hood/trunk air gaps/joints to see if they are even & that the doors/hood/trunk open & close OK. If they won't then something is off somewhere.

When you weld the sheetmetal floor to the sides of the sub fame connector there are two basic methods (A) weld it solid or (B) stitch weld passes. Which is the "best" method just depends on who you talk to. A solid weld end-to-end "theoretically" should be the strongest. But if a crack should develop at some point in the weld, it will follow the solid weld bead and eventually run to the ends. A stitch weld pass theoretically shouldn't be quite as strong. But if a weld crack should show up, the many gaps between each weld puddle should slow down the progression of the crack.


There are also many different ways to attach the connector tubing to most types of factory unibody sub fame "stubs", again it just depends on who you talk to. Depending on the shape of the stub you can weld the connector to the sides, backs/fronts, or to the bottoms of the stubs. Or you can get tricky & slip the connector tubing inside the stubs (and use additional plug welds) for a stronger load caring joint at each end.

DILLIGASDAVE wrote:Yea, level & square the car on the jack stands. No reason to "build" any unwanted diagonal twist into the body/chassis by mistake because the car wasn't sitting level on the stands. Once you get it to what you think is square/level on the stands, walk around the car & check all the fender/door/hood/trunk air gaps/joints to see if they are even & that the doors/hood/trunk open & close OK. If they won't then something is off somewhere.

When you weld the sheetmetal floor to the sides of the sub fame connector there are two basic methods (A) weld it solid or (B) stitch weld passes. Which is the "best" method just depends on who you talk to. A solid weld end-to-end "theoretically" should be the strongest. But if a crack should develop at some point in the weld, it will follow the solid weld bead and eventually run to the ends. A stitch weld pass theoretically shouldn't be quite as strong. But if a weld crack should show up, the many gaps between each weld puddle should slow down the progression of the crack.


There are also many different ways to attach the connector tubing to most types of factory unibody sub fame "stubs", again it just depends on who you talk to. Depending on the shape of the stub you can weld the connector to the sides, backs/fronts, or to the bottoms of the stubs. Or you can get tricky & slip the connector tubing inside the stubs (and use additional plug welds) for a stronger load caring joint at each end.

Great info Dave, thanks.

I like the plug weld idea and will prolly stitch weld it.

Bill

When i did my cobra two i put it on 4 ramps all the same so it was sitting on the tires just like normal. I didnt cut them into the floor but the way they fit i was able to weld quite a bit to the floor in sections the length of them also i welded a piece of roll bar between my rear frame rails about 6'' behind the center of the axles just to help stiffen up the rear frame section. Its working good i guess it always pulls the wheels dead even and launches straight like in the avatar.

When I did my Pinto I had the car on stands under the frame rails (no load on the suspension). Interesting enough on the Griggs Racing site they say to have you suspension loaded while installing subframe connectors and that is how I did my Falcon. I have not driven my Falcon yet but don't really see any difference yet.

As far as the front I like to trim out the center of the stock front subframe and recess the new on inside. This allows you to weld both sides. In the case of my Falcon the stock front stub is the same height as the 2x3 tubing I used so I trimmed the floor inside the car which allowed me to weld top and bottom right into the stock stub.

Here is the top of the floor trimmed out. After I trimmed the bottom section and slid in the 2x3.


I don't have a picture that shows it better but here you can see how the 2x3 rail is inside the stock front stub. I ended up having to cut out my rusty floor boards in this car but normally I just trim top and bottom.

Thanks Jason. That gives me some more good ideas!! I like that X brace, should be pretty solid now!!

Bill

FWIW, when I was checking into this, the consensus among fox chassis people was the car needs to be on an exhaust shop type lift, or 4 ramps, or ramps in front and jack stands under the axle in the back. Basically supported by the suspension and not the unibody.

I did my '68 Dodge the other way and the doors never closed the same after the subframe install.

BigBlockRanger wrote:FWIW, when I was checking into this, the consensus among fox chassis people was the car needs to be on an exhaust shop type lift, or 4 ramps, or ramps in front and jack stands under the axle in the back. Basically supported by the suspension and not the unibody.

I did my '68 Dodge the other way and the doors never closed the same after the subframe install.

That is what Griggs specializes in and that is pretty much what I have heard.

On thing I forgot to mention Bill is that where my front and rear outriggers (right term??) go to the rocker panel I welded 1x3 to the entire rocker panel. I have seen others just put a 1/8" plate here (4x6" ish) or plate the entire rocker panel to help stiffen up older mustangs. My goal was to get the car as stiff as possible with no roll bar so that is my reason for the X and the extra rocker bracing. I can jack up the passenger rocker panel in front of the rear wheel and the drivers will come off the ground in about 1/4-3/8 of an inch.

If you install sub frame connectors and/or a roll bar/cage while the car's full weight is sitting on the suspension compressing it, it is very possible that any unwanted/unseen diagonal body/frame twist will be built into the car & set in stone permanently when your done.

This "diagonal twist" can be caused by height differences from any unknown differences in spring rates from old/dead/worn springs, height difference from worn/sloppy suspension bushings, differences in suspension preload, even slight air pressure differences can effect things.

If your having problems getting the doors to open/close when the car is squared/leveled on stands, (and the engine/trans is in the car....and you don't have old worn door hinges ), your probably placing the jack stands in the wrong spots. Usually the front stands support the frame rail as close to the front axle C/L as possible. If you decide to place the front jack stands back from the front axle C/L, say all the way back at the frame "stubs" (around the firewall area) you most likely will cause door fit problems (especially if the engine/trans weight is in the car pulling down on the nose.

The best idea is to pull the engine & trans first before doing anything so you don't run the chance of the welding ground path going through the assembly by mistake. Same is true for any high dollar electronics, and expensive adjustable shocks....remove them to be safe.

On a side note if any car has ever been abused/crunched/crashed/etc, etc it's a good bet that some part of the body/frame somewhere is going to be bent/twisted/tweaked no matter how well any previous "body shop" repairs were done. You won't know for sure how bad things might be unless you measure everything & measure again. Measure wheelbase vs body landmarks, measure frame landmarks front to back, side to side, and diagonally.

That makes good sense Dave.

When I said it binds the doors, I had the stands on the frame stubs.

So if I put level stands under the K member and level stands at the lower control arm mounts, check all gaps, etc., I should be golden!! The car was hit at some time on the right quarter panel hard enough to blow out the little quarter window. I found the glass in the car when I pulled the interior panels.

Measure, measure, measure.

Thanks again for the info!!

Bill

I've always done the Foxes on the rear frame stub before the rear floor foot well and the front on the subframe or k-member under the front control arms. Use some thin plywood as shims under the jack stands. I did this on my 87 Mustang and proceeded to cut out most of the floor. It never moved around at all.

jbozzelle wrote:I've always done the Foxes on the rear frame stub before the rear floor foot well and the front on the subframe or k-member under the front control arms. Use some thin plywood as shims under the jack stands. I did this on my 87 Mustang and proceeded to cut out most of the floor. It never moved around at all.

Cool, thanks John!!

Bill