The exact same thing happened to my 91 744- odom and trip aren't working, but speedo is fine. It was out for about 9-10 months, then suddenly started working, but intermittently! I heard a clicking from the inst. cluster and figured it was a gear loose, but I wasn't comfortable ripping my dash apart back then, so I took it to a volvo specialist (The Volvo Shop in Rootstown, OH- nice people, very knowledgeable) They discovered that for the 700 series Volvo used a little electric motor to drive the odom, and that it was being flaky, hence the intermittent odom. They said they couldn't service or replace the motor w/o getting a new cluster w/ roughly the same miles. That's what I was told, maybe someone knows where you can get the motor...? Apparently, Volvo went back to the same mechanical style odom (with the small gear) in the 900 series that they used in the 200 series... Bad news for us 700 owners. Short answer to your question, no, the parts from a 200 will not work in your 700. Maybe others know better what we can do...?

John
'86 244, ~200k, beige "*snap* dammit!" interior
'91 744 ~131k, babymobile