Need Someone with 89 Specific Manual - Speedo Question

[JRA2000TL]

I installed a new speedometer cable in the 89 last night and replaced a few bulbs from a spare j/y cluster I had lying around. My speedometer still tends to jump around quite a bit, even after oiling the speedo head with some air tool (machine type) oil. I'm thinking the speedo head itself is bad.

Without taking the spare cluster apart, I need to find out if the speedo head is molded into the cluster somehow or if I can disassemble my existing cluster and swap out the head from the extra one. (I want my odometer to stay the same).

My 90 and 95 manuals have the different speedometers.

 

[rbruso]

The speedo head can be unbolted, but it might just be easier to disassemble the odometer on your replacement cluster. I did this when I fixed my bouncy speedo several years ago. That way you can have it ready to go and just swap, rather than have your car down for the entire time it takes to pull the old one, swap speedo heads and reinstall.

The odometer comes apart and goes back together rather easily. Just take your time and be careful with the little gears and shafts that run from the speedo head. If you take the endmost number off you can slide each one away from its neighbor enough to be able to rotate to the correct setting. You can then marvel at the engineering that went into mechanical odometers in the pre-digital days.

 

[jelloslug]

Have you checked the speed sensor on the tranny?

 

[JRA2000TL]

Have you checked the speed sensor on the tranny?

No, the odometer works but I'm not sure if that's related to the tranny speed sensor. Even when my speedo needle was flopping around to 140 and past, the odometer "kept up" with the approx. corresponding speed the car was going.

 

[rbruso]

Have you checked the speed sensor on the tranny?

The VSS on the transaxle feeds the computer. The odometer is run from a gear driven by the speedometer, which is driven by the speedo drive cable from the transmission. Rube Goldberg could probably have come up with some more convolutions if he had tried, but Ford did pretty well.

 

[JRA2000TL]

There must be several pieces to the speedometer head since the odometer appeared to maintain the current "speed" according to how fast I was going (i.e. it wasn't turning rapidly if I realistically was doing about 40mph but the needle jumped to 140mph). Makes me wonder if the actual speedometer needle itself is connected to a little wheel which, in turn, is connected to another "main" gear running the odo.

It still reads speeds it just wobbles around alot. I'll change it out with this spare when I have time.

 

[rbruso]

The speedo cable goes into the speedo head. The head has a gear off the side that is direct drive from this that goes to the odo. The part in the speedo head that is driven by the cable then induces motion into the needle drive mechanism.

The odo will always track the speed of the cable. After the head wears out, above a certain speed the spinning part can get too close to the needle pickup stuff, inducing more motion than required. Thus the crazy high neeedle (and the wispy scraping noise that usually accompanies it).

 

[jelloslug]

The VSS on the transaxle feeds the computer. The odometer is run from a gear driven by the speedometer, which is driven by the speedo drive cable from the transmission. Rube Goldberg could probably have come up with some more convolutions if he had tried, but Ford did pretty well.

The VSS is driven off of the same gear as the speedo cable connection.

 

[JRA2000TL]

Sorry to keep beating this dead horse, but tonight I removed the speedometer head from my spare cluster and, very carefully, swapped it into mine. I took the car out for a test drive to see how it worked. The needle seems to have "seizure" up to 30mph; but after that, it's smooth and accurate. It doesn't flop around or chirp as it used to, and the only wobbling is up to the 30mph range. When I installed the cable, it came with speedo cable ****, so I lubed the cable :laugh_ti:. Maybe I should put some lithium grease on it?

Like I said, 30mph+ it works great now...but 0-30 it wants to wobble around. Should I look at at VSS or that lower cable connecting to the tranny? Don't know much about that stuff; but I can always keep researching.

I think I'm going to order an 89 specific shop manual since there are some differences between the 89 and 90 models.

 

[jelloslug]

Have you replaced the speedo cables?

 

[JRA2000TL]

Have you replaced the speedo cables?

The upper one, yes.