after having such great results upgrading the suspension on my wife's Duster with .990 T-Bars, SuperStock rear Springs, PST Bushings, KYB Shocks, etc...

now I want to get my 70 Coronet R/T a little firmed up in the rear, the OE springs have ALOT of sag and my tires are rubbing on small bumps w/ nobody in the rear seat and a full tank of fuel.

What kind of upgrade/replacement springs are there for B-Bodies that bolt right in?

I looked at Super Stock springs, but not necessarily wanting to make any modifications other than bolt-on if I don't have to. I'd also like to retain my rear sway bar if I can.

Depending on your desired ride height, we offer a great dropped spring package for the B-Bodies. I run them on both of mine!

I looked at the Hotchkis springs on their website...pricing is a bit higher than I'm looking for on this particular application.

I'm still leary of the MP XHD springs as there has been several posts about how the quality has gone downhill in the last few years.

Just remember you get what you pay for. If the deal seems too good to be true, it usually is!

There were a number of different springs available for each model depending on engine and other options. If you are not increasing the front spring rates (t-bars) I'd be very hesitant to increase the rear spring rates. I don't have books for 1970 and newer, but with a little digging (maybe asking over in restoration or the Hamtramck-Historical website) you can find out what the factory suspension packages consisted of, including the Heavy Duty options.

Stanley Parts has a number of leaf options, some even cross ref. to factory numbers. They're based in Harrisburg. See here (Allentown retailer's website) for choices:
http://www.stengelbros.net/Dodge-Coronet-Charger-and-Super-Bee-Leaf-Springs_c_465.html

Engineers generally aim for 1 million cycles on a spring. Leafs and coils will then flatten/ compress/ and lose some rate. So yours very well may be lower than new. Without other info., I assume leafs will start to go downhill around 75-90,000 miles. Shorter life if overloaded, twisted (eg drag race start), or otherwise pressed to their limit.

what about mono leafsprings?

On an "E" I started with MP XHD springs. Ride height as new was a little high. With use, they dropped and it was a little low. Also spring rate seemed low vs beefed front T bars. Not balanced.

The fix was easy and not expensive. I had a local spring shop add one full leaf to the springs for $100 and change. This service got the ride height (+~1") and spring rate where it needed to be. Spring rates are approx:

stock: 120 lb/in
XHD: 140 lb/in
XHD + 1 full leaf: 170 lb/in

Thanks for the input....being that this 70 R/T is a *Cruiser* I ended up going with the MP XHD springs from Amazon.com...since I have a Prime account I get free shipping and they were 119/each....I'm sure Amazon will loose money on the free 2 day shipping on those!

swapping springs turned into a project that has some creep to it...

new springs, shackles & bushings, U-Bolts, Hangar Bolts, and I broke one of the studs off of the Drivers Side hangar, so I've gotta pound it out and replace it..

I gained about an inch of height in the rear with a full tank of fuel. The rear of the car is SOLID now, it's not mushy and bottoms out on anything I go over anymore, but not so harsh that I'd dare call it rough.