I recently purchased a 67 with a bad rear end. I want to find a replacement that includes disc brakes, as that conversion needs to happen too. What do I need to know, as I'm looking at salvage yards and used vehicles? What is the better option for power?
Brooke67, there are a few choices, all with different pros and cons. Disc brakes in the rear really aren't a big deal for these cars, unless you intend to use it on the track. They are more resistant to fade, but that only matters if you're getting to high speeds and stopping again and again. Your front brakes do all the work - about 80%, so it's unlikely you will notice any benefit to stopping power with rear discs, if that's what you're looking for. Whatever you choose, make sure you use a combination (including the proper master cylinder and proportioning valve!) for your combo.
All that said, the easiest and least expensive choices for your car would be stock axles. You don't have to mess with them or mod them. 8" is actually my favorite for these, due to its lighter weight and greater efficiency. If you have some kind of torque monster "I can stop the earth from revolving" engine and run slicks, you probably want the famous and bulletproof 9". Both of these axles have plenty of disc brake options. You could check out SSB or Wilwood if you need a kit to convert.
The 8.8" Ford axle is also common, but you would have to measure things carefully to make sure it's going to be the right width for your car. It's pretty much in-between the 8 and 9 inch rears in terms of strength and efficiency. It would require you to understand cutting and welding, because you'll have to remove tabs on the axle tubes without warping them, and then weld on new attachment hardware. Ford Rangers have 8.8" axles, but most of them are offset to one side which does not work well with our cars. Additionally, they have C-clip retainers, which means that if something in your pumpkin fails, or the clip gives out, the axle and wheel on that side just slides right out of the tube. For a lot of racing, there are requirements to improve that retention mechanism.
A lot of the 8.8's will have discs, and a lot of the Explorer/Mountaineer ones will have limited slip with 3.73 gears. But to be honest, the type of LSD they have is not a good one, and requires maintenance about every 30k miles. Not worth seeking one out for this feature, IMHO. If you want limited slip, just get a good Tru-Trac and put it in the axle you choose. Don't mess with clutch type LSD, because it's not very good and wears out fast, especially if you are really using it.
Lastly, if you have an i6, the old 7" axle ... aw heck. Nope. It just sucks. Don't bother. =) Best you can say is that it's light and frail.
No matter which you choose, just be sure you're getting the right width to start with, because it's a pain in the rear to change that.
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