My 65 impala SS was swaped over from the orginal PG to a 66 Saginaw 4 speed, engine is a 327/300hp. The problem is that the car sits low in the back due to incorrect tires, I am going to 15 inch correct diamater tires in the next few weeks but it sits low in the rear right now and the transmission leaks fluid out the back, I changed the rear seal and that didn't solve the problem, when I went to restore the rear brakes, with the rear up on jack stands and a more "normal" rake to the car there was no leak, the car was not jacked up excessivly high during the brake work, more like a car would sit with the correct springs and tires installed. When I put the car back down in its current rear end low the leak returned.
Is the leak because the transmission is sitting at an angle for long periods or should that matter? If you parked on a hill the transmission shouldnt leak.

The angle does not matter...it should not leak if everything is right. You could have a groove worn on the splined part of your drive shaft yoke that slides in the transmission...if so it will still leak with a new seal. Go to the parts house and ask for a seal and speedy sleeve kit for your transmission. The kit contains a tool to install the speedy sleeve...this will drive on over the wear surface on your yoke. Clean everything good and put a little lock tite under the sleeve before you install it.

Thanks, I will try that seal

Kurt

Make sure your transmission's rear bushing is good, also. If it's sloppy, the seal won't work well.

Also, some yokes have a small hole right in the middle of the back side, hidden by the U-joint. Leakage through that hole can mimic seal leakage. You can weld it up or plug it with a chunk of lead.