I'm putting an automatic frame (and C4 suspension while it's apart) under my '69. I reached my patience limit a while back with how difficult it was (read: Nightmare!) to remove and install the five speed (Doug Nash 4+1) each time I had to do clutch or trans work. The stock crossmember weighs 22 pounds, according to my garage scale. Just curious what some of the group has done to their's, and what weight did they end up with, while still retaining something that has some structural integrity.

Thanks,
Mike

 

How are you installing the C4 suspension?

I fabricated a new crossmember and drilled large holes in it. The stock crossmember is probab;y also heavier than 22lbs, I don't know how much heavier but definitely much heavier than that. I'd guess it to be well over 30. Did you weigh it?

 

How much does yours weight?

 

According to my Wal-Mart bathroom scale the crossmember is 22 pounds. It seems to be reasonably accurate, give or take a couple pounds, I'm sure.
The suspension is going in the regular old way. I cut into the frame's rear kick-ups to install some mounting plates to bolt in the trailing arms. I used an '80 batwing to mount the stock differential (it's 15 pounds lighter than the iron cover and steel crossmember combination, while also allowing easier installation of the toe link bracket. I drilled and tapped the casting for the toe bracket, similar to what you had done in one of your CAD drawings). I'm presently using cut and lengthened steel halfshafts for the mock-up, but those will be replaced by shortened C4 shafts to retain the stock C3 track width (I want to retain the 15 X 8 aluminum wheels for street driving periods). I've notched the frame in a few spots so that hopefully I'll be able to stuff some reasonably wide track tires inside the wheel well now that the trailing arms aren't the limiting factor.
The front is going slower (been busy with a family medical emergency lately), but I'm currently working on a custom crossmember that will relocate the lower A-arms and enable the use of a transverse spring (or coilovers if I find a bunch of extra money in my pocket some day). As this will be the stock C3 track width also I'll need to narrow the TL spring too. I'm currently in the process of modifying one of them. Other than just time and effort it looks like it ought to be feasible. I made up a little fixture to bolt up to the front knuckles to let me set the caster before I weld in the upper A-arm brackets. Lastly, the rack. The change in track width will likely cause me some bump steer issues, but I don't know the extent yet until I get the front suspension tacked in. If it's minor I may stick with the rack I have laying around, or if it's significant, I may have to spend some time at a junkyard measuring racks to find one the right width. I figure I'm still a couple weeks away from having to worry about that.
Brakes will be Wilwoods. I want a decent lightweight caliper and wide rotor that will still fit inside the 15 inch factory aluminum wheels. Wilwood looks to have some that will fit the bill, and still be reasonably priced.
So far it looks like the biggest PITA of this conversion will be the removal of the body from the stock frame to the new frame. I'm not looking forward to that whole process.

 

Jegs and Summit both sell crossmember kits, just make it. It's basic tubing with a drop. I think you also get them from kit car catalogs like Speedway. Most are under $100.

 

What C4 suspension do you have??? I don't get it, an 80 batwing and an iron diff? Where's the C4 stuff or do you have C4 rear hubs and dog bones and the toe control setup (I drilled my old batwing indeed, it was visible in the pics, not only in the cad drawing) What do you have on the front? C4 suspension corners, a custom spring and looking for a front take off rack??? Or do you have a tubular frame coming? Do you have pics?

I could have sworn the crossmember was heavier than 22 lbs, I don't have mine anymore so I can't weigh it. Sounds like a nice project you have there.

 

I started out with a '95 front and a '92 rear suspension that I had accumulated a few years back for spare parts for my '84 turbo and my 1951 Chevy P/U with C4 suspension (and similar turbo setup). After looking at the physical size of the C4 diff housing I was concerned that I might have to cut the rear tunnel area to make it fit under the car. I don't mind cutting the crap out of the spare frame (bought on ebay), but I didn't want to slice up the underbody for this project. Additionally, the C3 diff seems stronger, it fits the tunnel, and I have half a dozen different ratio rear ends laying around gathering dust. I used the '80 batwing due to its reduced weight, and the packaging improvement it provided when installing the toe control bracket behind the housing. (I don't know yet if the spare tire is still going to fit.)
I started with the '92 rear knuckles, but the sheer width of these things were going to prevent me from keeping the stock C3 track width without cutting into the battery box and jack storage tray. I had some 84 rear knuckles laying around from a previous project, and as they were much narrower, I just swapped the newer '92 bearings into them. I positioned the knuckles at the appropriate wheel base/track width location and then cut&welded plates in the rear kick-up area for the dog bone front brackets to bolt to. At this point there was interference with the knuckles and the batwing mounts at full suspension upward travel, so I sectioned three inches total out the the batwing width and had it rewelded by a reputable welder (I'm not at my comfort level yet welding aluminum).
The front is from a '95 that I bought years ago for parts to put the big brakes and calipers on my '84. I'm currently working on a front crossmember to locate the lower A-arms and also house a shortened TLS. The spring came with the front end, so it's a freebie to try to reuse. I'd like to also use the stock rack that came with the suspension, but as I mentioned before I don't know yet what the bumpsteer severity would be with it. It'd save me a few bucks if I could use it, though. I also still have no idea of what interference issues I'll run into with the steering shaft and radiator area.
Don't have any pictures taken yet, but I can do that. I've never uploaded any pictures to the forum so I'll have to figure out what it takes. (Also, gimme a bit of time to clean the garage. A lot of us like to look in the background of the photo and things are a bit disorganized, okay, a lot disorganized, at the moment due to a lot of recent travel and not enough time to properly pick up tools and stuff.)
I appreciate your questions and interest.
Mike