My 75 has a dealer installed a/c unit. The lower pan in the front trunk was cut out years ago by the dealer. Has anyone tried to fabricate cross bracing to tighten the front end? I think the structural integrity of the unibody was compromised by this "dealer authorized" surgical procedure. Interested in your thoughts. Thanks.

if it's just the sheet metal behind the front part of the trunk after about 3" and along the sides 2" from the front sub frame box it should be ok.

looks bad but the strength is in the box sections

Yes. Your dimensions accurately describe my set-up. The cut out begins about 3" from the front and I have about 2" to the box frames on each side. Thanks for your help.

I suppose what I lost in the transaction was the toe hook (mounted in that section of the panel removed) and drain tubes.

there are more effective tow hooks that bolt on to the front torsion bar mount. search for it in member vendors I think some one here makes them.

I dis-agree ...

I think any cutting that close to the front A-Arm mounts has to have a negative impact.

I think the only forces put on that section is horizontal axis locating the front of the A-arm, most all loaded force is placed on the back mount at the cross member.

if there is a lot cut out of the front vertical panel at the nose I would worry more about that!

Restoration Design just started making a perfect panel to fix this if you want to.

They totally rock when it comes to Porsche repair panels.

John

unless he wants to keep the a/c if it is working....

Doh! I did not catch that part..

John

I just went out to put my '75 back in the garage and looked at it, and it looks like there is a lot of "bracing" on the front of the later cars. if it's just a street car I don't think its worth worrying about.

if it keeps nagging at you weld in some 3/4 square tube along the inside edge.

Yes, 75-76 do have a little more structure to them due to the heavy bumpers. The front bumper brace runs almost the full length of the wheel well whereas the 73-74 only goes half the distance. The U shaped brackets had some strength too. The 70-72 do not have this extra bracing. Early cars are the ones I would be concerned about.

comparision

cracks can result that run towards the front control arm mounting points. plus there are bunch of holes for the hoses that would have to be welded up and in most cases the pass side engine shelve gets butchered. as noted installs vary. somewhat clean to out right dog crap.

I have invested quite a bit to have working a/c, so I want to keep that. I've thought about welding in some "x" cross-bracing just above a/c unit to get some rigidity back. With a uni-body it seems to me that this floor pan acts as a diaphragm to resist some torsional forces between the box beams.

Heres what I did. Not sure if it added any structural rigidity, but it should not let cracks form and travel.
Click to view attachment
Click to view attachment

THe biggest loads at the front mounts are twisting forces from stock rubber bushings or tight polygraphite bushings binding. There are no loads transfered from the torsion bars through the front mounts, and the side loading from cornering is much smaller at the front than at the rear.

If you've ever looked at the floor of the front trunk on a 911, you'd worry less. 911's have a hole, albeit with a flanged edge, that covers practically the entire area between the two A-arm mounts.

if anyone has evidence of stresses in this area, please post pictures. i have not seen much movement up there. the rear is a different story. the

When I started to take my 75, that had A/C, apart in 1991 I had to repair a tear/ crack on the frame. It was near where the front A-arm bolts up on the driver side. I'm pretty sure the car was not an autocross/ TT car. The crack was about 1.5"

This car had the full trunk floor intact.
Cracks occur right around the a-arm mounts as a result of tight bushings and rough roads.
Click to view attachment

I've seen pictures of a bad bushing literally ripping the front mount off the pan.

right along th spot weld line