A lot of 544's have working speedo's with broken odometers. Does anyone know of an aftermarket electric odometer device which can be adapted?

Peter:

A Dutch friend used a wired bicycle odometer to read distance and speed in kilometers on his 1800E imported from California. The pickup was attached to the front suspension and sensing magnet was attached to his front wheel. Of course you could also get a rally instrument, which might be more accurate and the ultimate odometer replacement.

The odometer can be repaired, either with a new odometer gear or by drilling through the shaft and fixing the broken gear shaft with some fine wire and epoxy.
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Cam a.k.a. CVOLVO.COM

Have you pulled the instrument cluster? If not, I'd say that should be the first step, so you can take the thing apart and see what is going on. Frequently the shafts and gears are making proper contact, but the little ratchet/dogs on the number wheels are worn enough that they don't make sufficient contact. Sometimes they can be fiddled with so they will make contact again, or the offending wheel can be replaced with one from a junked unit. Sometimes the drive worm gear is worn or has slipped out of position. If I remember correctly (it's been a while since I had one apart), there is a lock pin in there somewhere that can be reshaped, and that helps to make that gear make proper contact again. I've had some, at least tempory, success with that kind of repairs, but I must admit that they didn't last more than a couple of years and that, eventually, I replaced the whole cluster with a healthy one.
Bob S.

I've been through a lot of Volvo odometers in the past couple of years. The primary problem seems to be the small drive gear where it takes off from the speedometer shaft. The little gear seems to wear out before anything else does.

Sometimes you can pull the little pin that holds the gear in place on its shaft and turn the gear end-for-end and have enough un-worn teeth to engage and keep the odometer working.

Probably the best solution is to take the whole speedometer or even just the worn gear to a speedometer shop and have the gear replaced. Nearly every town of any size has a shop that specializes in speedometer work for commercial vehicles like taxis or delivery trucks where the speedometers must be corrected and certified. They carry every imaginable part.

Good luck!

Steve