And ANOTHER problem... ;)
An auto parts store will sell a lubricant specifically for speedo cables. The general procedure is to tear into the dash and remove the instrument cluster. Once the cluster is loose, you need to squeeze a hand or two in behind it to trigger the release on the cable where it attaches to the cluster. I have relubed speedo cables many times, but I can't remember doing the Aerostar, so I can't say exactly how to release the cable.
Once the cable is separated from the cable, take note of how far in the core of the cable sits in the connector and then pull the core of the cable out with a pair of pliers. Take care that it doesn't get away from you, as the lube remaining on the core will leave nasty stains on the upholstery and carpets. The core will likely be about 6 feet long.
With the core out, squirt a healthy shot of lube into the cable sheath. If you want you can smear some lube on the cable core, too, but generally the lube squirted into the sheath gets distributed when the core is pushed back in. It may help to spin the core as you push it back in, particularly when it has to re-engage at the trans end. Make sure the core seats as far into the sheath as it was before you took it out.
Reconnect the cable to the cluster - a little twisting and wiggling will help the core to engage the cluster properly. Then reassemble the dash and enjoy the sounds of silence (or all the other rattles and buzzes you hear in a van this old).
Oh, yeah. Stock up on band-aids and antiseptic before you start. You will shed blood trying to get your hands behind the cluster to disconnect and reconnect the cable.
Good luck.
Cheers,
Eric


