Subframe build and adaptor plate mods

When I got the new motor and powerglide, I decided I wanted to put it as far under the tunnel as I could make it fit. This would free up alot of extra space under the hood so I wouldn’t have to worry too much about fitting the batteries. 

I knew I would have to build another cross member as the original motor mounts were about 20″ In front of the motor, while the transmission was mounted to the stock transmission cross member. This new section would have to be the main restraint for the massive amount of torque this motor can make. That’s how I came to a decision of replacing the transmission cross member and building a subframe to carry the motor transmission combo. 

I had found a frame dimension drawing for my frame online, and sketched up what I wanted the new subframe to look like. After getting some more dimensions off the frame, I went over to Solidworks and drew up a weldment using 3×2 box steel. Solidworks automatically calculates the angles and can generate a cut list which makes buying enough material and knowing how to cut it a no brainer. 

I ended up picking up 24ft of 3 x 2 x 0.120 wall box steel, 5ft of 1/4 x 2 plate and 2 – 1ft pieces of 1″od tubing for about $160 at the local race shop. 

This was quickly cut up following the cut list and the rear cross member replacement came to life. 

Before tack welding it together, I put the center section on the Bridgeport and milled slots for the transmission mount and on the bottom, a hole to access the bolts for mounting the transmission. This is the same idea as the stock cross member used. 

After this was tacked together, I found it sat a little lower then I liked. So before welding the bolt flanges to the ends, I notched them out so it would sit closet to stock rear cross member height. 

I then cut the 2 – 24″ pieces that are the straight sections that surround the motor and transmission. I talked these on and bolted the subframe to the car to fit the last 4 pieces. 

I knew where the front pieces that would bolt the frame would roughly go, and now I knew where the straight subframe rails ended, i just had to join them. Solidworks calculated an angle close to wheat I needed, but I needed to adjust them. This took a couple hours to get everything to fit right. Once it all fit, I tacked it up and removed it from the car to be fully welded. 

I was able to borrow a welder from my father-in-law Rick. Since I like to try doing things that I am not good at, I borrowed the tig welder. 

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