My xj came with an np242 tc. Out of necessity, I installed my 88 np231. The speedometer cable mated up fine, but a couple of days ago the speedometer quit registering. The odometer is fine. I'm confused... Is there an electrical component to my speedo? I thought it was totally cable driven. If it means anything, it has cruise control.

 

The prognosis isn’t good. Looking at the drive end, there appears to be only one thing being turned by the flex shaft. It is difficult to take a picture down the input shaft area, but I did run a dental pick down the inside and there is only the one solid square tube. On the other side however, the odometer is the first thing driven by the blue/white worm gear set. The speedometer needle is driven by the tiny wire shaft with the clock spring on it. I’d say if you have odometer and no speedometer, it’s a broken shaft – or mechanism going to that shaft. The speedometer photographed is out of a '90.

 

If you have cruise control, there is a 'sensor" about 6" back from the cluster but it won't cause your issue. The speedometer/odometer are purely mechanical.

 

I took it out today and on some rougher roads, I looked down & it was working! Bumps might have done it. Thanks guys.