Need Help! Changing Rear Chassis Springs

[Rick Parker]

I am in the middle of changing the rear springs on my car. I am out of my element in this part of the car consequently I have put this off for quite a while, but today was the day. The shocks ar Alden coil overs with only the rebound being adjustable. The current springs are 10 inch rated at 240#. The replacements I have are 8 inch rated at 300#. Is there something I am overlooking by replacing the 10" with an 8" as long as there is enough thread adjustment on the body of the shock absorber. The reason for the change is that sometimes the rear suspension bottoms out on some bumps while driving, this is only with me (a svelt 210#) in the car. Aside from going on a diet.??????...........am I on the right track by putting on stiffer springs (?) Or should I be looking at the shocks? The existing ones are in good working order. Is the the additional 60# too much of an initial change (?)

Chassis Guru's!!!

With the frame rails on jack stands, I raised the center of the differential to the point that the chassis just began to lift off of the Jack stands and I measured the compressed length of the 10" spring in an attempt to determine an installed length of the shock (at ride height) so I would have a gauge to keep the ride height the same, short of getting under the car and measuring the actual ride height. The compressed spring measured 7.5" long at the point it lifted off. I neglected to measure the installed length of the shock itself (out of my element!!!) Is there a formula to calculate the comparative length that the 8" long spring would to be with the same load so I could install it at a precompressed free length and be assured that it will maintain the same ride height? I don't want to have to climb under the car several times in an attempt to set the ride height.
The image below is what the shocks & springs looked like before the body was installed.

Is this clear as mud???

Thanks guys

Rick