Sometimes, the gears jam if you try to reset it when the trip odometer's tenths place is near ".0" -- i.e., from about .8 through .2, I never push the reset. Sometimes you can see this jam when the digits don't line up -- one of the digits is turned higher than the others.

And once, despite this caution, it jammed on me anyway. And it was making a slight clicking sound!

I quickly found an empty street, and drove backward down it for a block or so. It unjammed, and then going forward all was well again.

Good luck.

Everything you need to know about fixing your gear is right here:
http://www.hyperocity.com/volvo240/volvoodometer.htm

As a rule, I never, ever, under any circumstances touch the trip reset button. Never as in like never, ever.
Others will say it doesn't matter. I'm just sayin'

I did the replacement in about an hour. It's a fairly easy job with the set of instructions above, actually fun. I ordered my gear from the site mentioned at the link above and got it in about 48 hours.

Dow

You need the tiny gear, in the speedometer, replaced. I think pushing that reset button can break an old/weak gear. IPD sells it.

Soooner or later they break. And from what you describe (everything works except the odometer/trip meter) the previously mentioned gear is the fix.

And I second Randy's suggestion of odometergears.com.

Did it break at reset? If you usually calculate fuel economy and got a drastically different result than what you would normally expect, then it broke between fuel stops.

At any rate, the aforementioned site also provides a link to instructions for replacement of this gear and it is really pretty easy.
--
'80 DL 2 door, '89 DL Wagon

Resetting the trip odometer is very hard on one gear in particular. You need a new gear.

Available at: www.odometergears.com

Randy