Both our '87 and '89 240s suffered the collapsing seat back problem.  At
first I thought it was because I'm big and fat (200 lbs) but then the other
one, belonging to my small light (100 lb) wife failed identically.

In one of them, I replaced the seats with a pair from a totaled '92 at the
junkyard for $100 (I actually did the swap in the junkyard parking lot in
about 30 minutes and left the bad ones with them).  The ones from the '92
lasted for another two years before failing in the same way.

I don't think Volvo ever fixed the design problem in the 240.  Replacing
them with junkyard seats is a short-term solution at best.

We never had this problem with our '76 or '78 260s.  I don't know whether
the older '70's seats fit in the late 80's mounting holes or if you can find
a decent set of 30 year-old-seats in a junkyard, but that's what I would
pursue if I had to do it again.

So far, we haven't seen this problem with our 850's.  Anyone ever try
squeezing 850 seats into a 240?

-RL