I'm sorry to wake up an old thread. I am interested in seeing how this project came out, particularly the floor and cross-member mods. I am currently planning the 518 swap in my Fifth and want to sort out those details before I jump in. Duke, where is the 500 how-to that you mention above. I searched and couldn't find it.
Thanks!
Fred

 

Must have been another post on this forum, or maybe something on Dippy.org. I honestly can't remember.

If you have even basic fabrication skills this swap isn't that hard, nor do you have to cut much up on the car. Only thing on the car that needs removal is the cross member that runs side-to-side between the rails up into the tunnel. Only part of it needs to be cut out. Right behind the bolt holes for the trans mount towards the center of the car. You have to remove this small section to gain enough room so the OD section of the trans can sit high enough. Obliviously, it needs to be replaced with something else when done. I've seen it done with 3/16" flat stock that was rolled to the proper curvature of the tunnel, or you can form box tube. Either way you need to pull the carpet back off the tunnel and make it so it sticks up into the interior rather than underneath. I won't interfere with the seats or anything and the drivers seat will even hide it.

I've got photos somewhere. Let me look.

Edit:
See here for photos of the tunnel modification needed: Gear Vendors Unit

 

Thanks - that is very helpful.

 

may have been a FABO thread. there is an extensive one detailing the modification to the torsion bar / transmission mount

 

it was at Farleys.

 

good shot of the cut away for the 518

 

Looks nice. I’ve done 2 of these. I welded channel on the top hidden by the console. Yes

 

I used something a little smaller but that sounds like it would work. I also welded in frame ties.

 

Ok guys I got the 518 loaded up for a performance rebuild. It’s an early model w/o the lockup converter. I’ve got an extra sacrificial trans mount. Does anyone have any pics on what you did to modify it?

 

This is Dad's car. Made the mount from scratch, but this is basically what needs to happen.

 

i modified the stock one to work

 

I had an early A518 in a Mirada the OD was activated by a simple push button switch. The trans tunnel needs to be cut, so does the crossmember. The small trans mount will not fit, simply use the larger "butterfly" type.

 

Thanks!

 

Wait, so does the trans mount AND tunnel need to be modified or can you just get away with doing only the trans mount?

 

The trans tunnel needs to be modified for a 518.
I had to cut the “transmission crossmembers” mounting bolt holes out of the upper “transmission crossmember”.
So basically I cut a vertical line up from just outside or centered from the upper transmission cross members bolt holes.
This eliminated the possibility of using a stock unmodified “small/ standard” transmission cross member, hence me using a larger unmodified stock “butterfly” trans cross member .
I believe the Imperials all came with the larger butterfly style mount, as did some Miradas.

 

The back of the trans has to raised up for the proper driveshaft angle to be maintained.
The angle between the trans and the driveshaft has to be downhill to the pinion a minimum of about one degree with the pinion rotated up as when under power.
The pinion has to remain " nose-down" relative to the driveshaft also a minimum of about one degree. In this way the two angles cancel out to prevent vibration.
Within those confines, you can do anything you want to. or have to.
Your driveshaft will be several inches shorter, exacerbating the problem.
As will weak rear springs, that cannot control the pinion angle.
As will big power that will want to raise the pinion up far in excess of the equilibrium point.
If you have torsion bars like an A-body, that cross-member has to bridge the two stubs in a manner that makes all three pieces behave like one, else the T-bars will tend to rip the stubs off the floor. With L-bars this is not an issue.

 

Everyone seems to do it a little bit differently. Here's how I did mine.