The original front differential mount on all first generation Z cars is just terrible. There's no way I was going to pay $50 for a replacement piece of crap that was doomed to fail again. I saw a much better alternative on Simon DeGroot's excellent website. So, I am attempting to copy his design. He uses a set of bushings from an Asian market Nissan car. I took a chance and ordered the Energy Suspension poly trans mount bushings. I then went on a quest to find some tubing that would match up. I started to hack apart a coat hanger bar (I was going to cross section it to make a smaller diameter into a larger one to precisely fit the bushings). Then I randomly found a piece of galvanized tubing at the local home center (I'll post the exact diameter soon - it's an exact, tight fit).
The stock front diff member was removed and then sand blasted.
I bought a 1 1/4 inch hole saw that was slightly smaller than the diameter of the tubing. I used the top of the old rubber diff mount and marked 2 spots in 15/16th of an inch from the center hole of the member and in the center vertically. I had no hopes of actually drilling thru the steel with the cheesy hole saw, but it made an excellent score mark in both spots.
Then I took a 1/4 inch drill bit and drilled several holes along this score mark. I used the narrowest sawzall blade I could find to cut out the hole.
I then used my chop saw to cut across the member. Marked the other side with my now almost totally useless hole saw. The 1/4 inch bit was also tanked, so for the other side I just made a bazillion relief cuts. I bent that saw blade so many times. I used a 1 inch grinding wheel in my hand drill to clean up the holes. I used a socket that was about the same size as the tubing - grind, try and fit socket, grind more, hammer socket in, grind more, etc.
Once the holes were both ground out fairly round, I had to attack the reinforcement plate on the upper inside part of the member. I couldn't break it loose - seemed like it was spot welded in place. So, I started to grind away at it. Very tedious. But, when I bent the inner part of the top, it broke loose a bit. I was then able to hammer and pry it out.
I used the rear cross member as a brace. I bolted it underneath the diffmember to try and keep it from bending out of shape when welded.
I inserted the entire length of tubing in the first hole. The extra length allowed me to make sure it was square. I tacked it in place and then cut off the ends. For the second hole, I welded much more of the round part before cutting.
NOTE: When welding galvanized metal, you must make sure that you are in a well ventilated area. Only weld in short bursts. Galvanized metal gives off a toxic gas when welded. Avoid it if at all possible!
Before welding the top seam, I hammered in a socket (Craftsman 23mm 12point) that had the exact OD of the ID of the tubing. This kept the tubing from going oval when I hammered the top seam flat, and it also kept the tubing piece from warping. It also served to remove any burrs or mess when I hammered it back out again.
Finally, I ground everything down and then sanded it somewhat smooth. The end product doesn't look nearly as nice as Simon's, but I think it will serve well.
Next up, butchering the original diff mount for use with this new diff member.....