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I posted last night about building and installing the subframe connectors on the 65 coupe. I'd planned on raising the front end way up with the forlift and mustang hitch for easier access for welding. I've been told to keep the car on the floor with the full weight of the car, or jack the rear up, but not the front. I realize you want the chassis in a 'natural' stance as much as possible so things don't get mis-aligned. Here is my reasoning and methodology....please dare to dis-agree....I need the input.

The 65 coupe is basically a shell, sans body panels, front end, engine...just about everything but the rear end. I have a trailer hitch mounted to it to lift and haul it around as a two wheeler, for now. Consequently the chassis is at its lightest weight possible. So lifting the front end to access the bottom from underneath should not present a problem as far as bend in the unibody is concerned. I used this technique to weld the underneath side of the floorpans as I could sit and almost stand under the car.

If the car is fully weighted with engine, steering, and drivetrain components, I imagine the subframe would then be "loaded", thus in its natural stance. That would be the case for waiting on the subframe connector install. If its a simple matter of flexing while the front end is in the air, I highly doubt there would a problem there as the light weight would provide rigidity in itself. I can also run a taut line between the subframes to measure any flex as I lift the car, if I need to check alignment, then adjust accordingly before welding the subframe connectors in place.

Am I totally off base here? I'd appreciate any engineering input here. Thanks.
 

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I can't offer any real engineering here, but I can give you my $.02.

If the car is not fully loaded with all components when the subframes are installed then it is not going to sit properly.

As you know, the Mustang uses a uni-body frame, which means the body IS the frame. Welding in the sub-frames when the body is not stressed at all by engine weight will cause things to be wrong later. Probably not terribly wrong, but wrong.

If it were my car I would wait on the sub-frames until such time as I had the car in a drivable condition. Then if I did not have a hoist that lifts at the wheels, I would take the car to a muffler shop and have them tack the sub-frames in place, after which I would weld them in solid at home.

Again, this is just my $.02.
 

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I think if everything measures up square then do it now. By square, I mean measuring the frame based on the dimensions in the Ford Shop Manual as well as door gaps, distance between motor mounts, or anywhere you think space would be critical. Why flex a weary frame and then weld the connectors on to make it rigid at that point? It seems that welding the connectors on now would prevent, instead of lock in, the sag on your 37 year old unibody, as long as all those measurements are within spec. In addition to the factory specs, I would also make sure the body is level, i.e. not twisted, meaning that the body to ground distances are the same front and back when the frame is measured to be square.
 

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I'd agree with Kent and benchcoupe at the same time. Benchcoupe is right, that if the frame measurements are within spec, you'll probably be OK. The problem is that the frame measurements are kinda sparse, and not accurate enough to take into account frame flexing and alignment from things like monte-carlo bars and export braces. There's a lot of slop in the specs, so you might be able to get by, but it'll take a lot of effort to make those measurements. Kent's method is the simplest: just wait until it's nearly all together, then weld it in. You'll be sure it will work then.

Can you be sure it will be in spec welding in the SFC prior to the drivetrain being loaded? I sure wouldn't bet my car on it....

What's the hurry? Think about it...
 

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Get the drivetrain in, run the front end up on ramps and jack the rear up by the pumpkin. Use jack stands under the rear axles. This is about as close as you can get without a drive-on lift.
 

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I read your post this morning and posted the next couple of paragraphs after I questioned the same issue of lifting the car vs. sitting on suspension. My car too is sans everthing even the rear end at this point. The way I figure it is that if I was confident enough to cut and weld in new floors why is the subframe connector any different?

I can see the valid point that all measurements would need to be close. However having a 35plus year old car sitting on suspension that is new and is putting new stresses on the "frame" seems that it would pust things out of alignment more that with everything off the car.

I still am not convinced waiting is the right/correct thing.

Prior post attached I think there are some valid points to both sides-

My first poston this matter####

If you have the rear of the car lifted and the front of the car is compressed, is'nt that putting more stress on the front subframe?

It seems that more stress on the front subframe would also increase the stress on the well known weak/flexable body. If there is more flex on the body when you attach subframes once you put the car back on the ground the stress/flex is now welded into the body by the subframes. Wouldn't welding them in under full suspension lock in any flex that your car would be experiencing already?

Right now I just don't see that having the car up in the air supported in its lifting locations is a problem. If the subframes are straight and true it will remain correct when welded in irregardless of the suspension.

I thought the idea was to lock the car in as close to factory as possible and keep the flex out.

I just dont see it.


second post#####

I still do not see/understand this. As I see it you are taking one frame and connecting it to a second frame. These two frames are already connected via the floors, roof, and rocker boxes. If the car is supported in all the correct lifting points, why would the full weight of the car on the supsension matter?

I thought the point of subframe connectors was to strengthen the ridigity of the body and frame, to keep it from flexing. If that is the point, wouldn't the body in a fixed position be desireable?

It just seems to me that if you are creating a full frame car( by attaching the subframes together ) It would be better to have the body in a fixed position.

If any one has manufacturers data on this I would love to see it.

Thomas
 

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With KKetell's help I may be on to someting.

The subframe connectors are not a frame. Only connectors and as such are not designed to take the full weight of the body. They are only intended to strengthen and reduce flex. If they are put on before the rest of the car is back together, they may become a under designed frame and will cause stress wher the car was not designed to have it.

As such. It may be wise to wait. Put the car back to gether and then install the sfc's.

I just had to think about it for a while from the other side and open my mind a bit.

Thomas
 

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Hey Dan -
I'll reiterate what I posted last night. Before welding in the connectors, I think the car should be fully (and accurately) weighted and driven around - in order to wear in any new/rebuilt suspension components to the point that the car is sitting just about the way it will for the rest of its pampered life.

Now, the reason I suggested this is that I've read several articles on chassis mods over the years and every one of them said this is critical to proper fitting of SFCs.

I've even read one or two that suggest you put a few sandbags in the driver's seat to simulate the weight of the driver.

All of this may seem like overkill, but I've read it several times, so I'm thinking there must be something to it. It kinda makes sense, when you think about how flexible a Mustang (or any old unibody for that matter) is.

So... I'm with Kent and Midlife.
 

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Personally i see no reason not to just weld them now with the front end raised high in the sky and the rear sitting on the ground as long as the car is level left to right. Its not as if jacking the car up will significantly change the weight ratio front to back by lifing the car a few feet, or how it will significantly change the weight being bridged through the car. What you really don't want to do is twist the body and weld the connectors in with the car twisted.
 

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Wow, after reading all the replies, I had to wonder about my wisdom of building the race car chassis on a couple of long I beams with jigs holding the car in place...

All I can say, is that I cut a substantial amount of material out of the car and was amazed at how sturdy it still was, albeit without a drivetrain in it.

Personally, I'd just put the rear end of the car on jackstands and put a couple of stands under the front frame rails and go to town.....I can't begin to remember how many chassis for street racers and track cars were modified this way in my younger days.....for the most part, they seemed to go straight *G* and all the body panels fit OK, IIRC.

This sounds like it's going to be a modifed car and there will be plenty of room for making everything to fit and line up, if my experiences were any indicator.

Good luck!
 
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