68 rear suspension problem

First off my opinion is don't even consider the air shocks, the upper mounts aren't designed to carry the wt. of the car which is what will happen, been there done that 20yrs. ago and read plenty of posts about cracked upper mounts, mine cracked and had to be welded, I had the very min. amount of air you could put but when they bottom out they are solid.

I'd solve the problem at it's root, you may have to change rims or tires. What rims are on it, what is their backspace? This is easy enough to measure by taking a rear wheel off, laying it flat face down and measuring from the rim lip (not tire) down to the mounting surface (the backside of the flat surface that touches your drum), this will give you your backspace. I have 15" rims with 3.75" bs and with 225 tires they just rubbed at the bulge of the tire so I'd say 4" would be the min. bs I could use w/o rubbing or a 215 wide tire would have probably cleared.

Please post your tire size and rim backspace and someone will have used something similar and can tell you if a different tire will clear. I wouldn't go stiffer springs either as you'll just ruin the ride when you don't have 1-2 people in the back seat.
Jon

+1 on what JonK said! Also, helper springs can change your pinion angle (NOT GOOD). If tires are rubbing on the wheel well lip, you could gently/lightly roll your wheel lip. If rubbing on the inside edge, different tire or wheels are the answer. As far as stiffer springs, a set of 4 1/2 leaf units from Maier Racing won't harshen the ride much but will help your problem as well as controlling wheel hop, if that's an issue for you.
HTH
Gene

Almost certainly your old springs are sagging. New, GT-rate springs will bring the car back up to height, and not cost a lot, under $200 for the springs, U and eye bolts, and shackles. Whether this will give your 17" wheels and tires the clearance you need is another issue.

Mustang Wheel and Tyre Chart

If the tires are contacting the body, new springs will reduce that, by raising the car to stock height, but either the tires must get narrower or the fender lip wider.

You don't need 4 1/2, 5, 6, etc leaf springs. Leave that stuff to race cars and bakery trucks. Even the BOSS 429 had 4 leaf springs.

I had the same issue with my 17's. I installed 5 leaf mid-eyes and a softer shock, the kyb gr-2's. I also rolled the fender and I now have no issues. Ride is definitely firmer but not a tooth-rattling ride.

Number of leafs isn't as important as the spring rate. Hell, even Chevys used a mono leaf on many applications. Since you suggested that your springs are worn out anyway, Start with that and don't worry about the quarter lip until you have solid springs in there. Sounds like you need em anyway.

Also, another question comes to mind: Why are you torturing people by putting them on the back seat of a 68 coupe? LOL!

I know my car is a 65 but I had the same issues as you are suffering. I swapped to 5 1/2 leaf standard eye springs with prothane urethane shackles. I am also running 17x8's out back and they do not scrub at all. Also my 9inch has 3 in axles tubes instead of the ones that reduce down on the early cars. I think it lowers the car about 1/2 an inch. Either way this solved all my rubbing issues, and a good amount of my wheel hop. Good Luck!

This is how it sits with 2 people in the car:

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