posted 06-11-2014 08:30 AM ET (US)        

http://i976.photobucket.com/albums/ae243/jsmith294/Cushions%20etc/ IMG_0789_zps289bce6c.jpg

In essence, the three bottom blocks provide slots for the pivot arm shafts and the fourth block functions as a cap.

I do not know if this design was original from the factory (I hope not) or a retrofit (the seat had been recovered). I do not like it. It is ugly and heavy. I plan to replace it with a much simpler design. Here is the prototype:

http://i976.photobucket.com/albums/ae243/jsmith294/Cushions%20etc/ IMG_0804_zpsf9d99f96.jpg

http://i976.photobucket.com/albums/ae243/jsmith294/Cushions%20etc/ IMG_0787_zps4e8b98b5.jpg

The design consists of two 3" wide pieces of plywood clamped together with 15/16" holes drilled through along the interface for the shafts to pass through. I plan to use seal the supports with epoxy and lubricate them with paraffin (the stainless steel shafts showed some evidence of wear when I removed them).

That said, I have a very serious problem. I need to know the proper spacing for the holes in order for the seat to have the correct kinematic function. The RPS forms a simple four-bar linkage. The angle of the RPS seatback depends on the relative spacing between the two pivot arm shafts under the seat and the spacing between the pivot arm block attachment points. If the two spacings were equal, the seatback would not rotate as it was reversed; it would remain at a constant (presumably vertical) angle. Making the seatback pivot block spacing larger than the seat bottom shaft support spacing gives the seat back a slight backward angle when the seat is in the back (facing forward) position. This angle would be mirrored when the seat is reversed.

Comparing the spacings in my original seat shows that the pivot block spacing was indeed greater than the shaft support spacing:

http://i976.photobucket.com/albums/ae243/jsmith294/Cushions%20etc/ IMG_0790_zpse4523472.jpg

If the old were supports are original, I am set. I just reproduce the spacing when I drill the holes on my new supports. However, if the old supports are homebuilt with an incorrect spacing, that spacing will not give me the proper seatback motion.

I have no access to an original seat, or even a reproduction. I would be tremendously grateful if somebody could measure the spacing between the pivot arm shafts at the bottom of the your seat.

Thank you, and apologies for the long post.