Hi all.. For anyone interested, I did finally determine the cause of the seat "rocking". Contrary to previous posts, the brand of hardware used for my seat pedestal was not from Springfield Marine. It was from Garelick Mfg Co, 644 Second Street, PO Box 8, St Paul Park, MN 55071-0008. On the web at
www.garelick.com and tel # 651-459-9795.
Sorry I don't have pictures. Actually I do have pictures, but I am unable to edit the dimension of them to fit in this reply.. sorry!
Garelick does not make the exact replacement pedestal, and they tried to interest me in a similiar but newer model. However, replacing the entire seat pedestal with a new model would have required separating the original pedestal floor bolts from the floor of the boat. I knew that removal of the original base would require backing the floor bolts out, and when the first floor bolt gave me trouble(didn't want to twist out and nearly stripped the head of the floor bolt..) I decided to leave them all in place. Instead of removing the original pedestal base from the floor of the boat I repaired the existing internal parts of the old pedestal with the help of a local welding outfit. (In the long run, repairing the original pedestal parts was cheaper anyway).
The best way I can describe what happened without a picture is that the shaft of the floor pedestal has an inner sleeve which adjusts height up and down, and this inner sleeve is attached to the "slide and swivel unit" on the seat bottom.
The whole seat along with the "slide and swivel unit" and the inner sleeve of the pedestal, still attached to the seat bottom, will separate from the outer sleeve and floor base of the pedestal, if the locking pin is held open and you lift the seat straight up. You need to separate the inner sleeve unit from the outer sleeve and floor base of the pedestal in this way.
If you look closely there is a cap on the top of the inner sleeve about 4 inches long, and this cap should be welded to the inner sleeve. The "slide and swivel unit" on the under side of the seat fits over this cap, and conceals it, but if the weld attaching the cap to the inner sleeve lets go, the seat can never be tightened. This was my case.
The welding shop re-bonded the cap on the inner sleeve, so the seat could be tighted firmly to the inner sleeve using the hand knob on the swivel unit. The seat with the "slide and swivel unit" and the inner sleeve attached was then slid back onto the base pedestal, where the inner sleeve height is now locked in using the adjustment pin on the outer sleeve.
..Unless you have this seat problem you may never be able to visualize this, but if you have the Garelick Mfg seat pedestal, and your seat is still loose no matter how hard you tighten the hand knob, this is problably the issue.
I have pictures which I can email. sorry I am unable to fit them in this reply. Feel free to contact me.
SMK