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Discussion Starter #1
First time posting, just bought a 65 convertible t-code with a 289 and c4, it had the original 65 cluster in it but the speedometer didn’t work correctly and the odometer didn’t move. I did a 66 cluster conversion and tested it out today and all gauges work normally but noticed that the odometer was counting the miles backwards, it was all set to 0 when I bought it off eBay. As soon as I drove down the street it went to 99,999.9 and then counted down from there. Any ideas what would cause this?
 

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Must be an Aussie speedometer , if water runs down the drain in the opposite direction ....why not an odometer that works backwards?.
I really have no idea .
 
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Check your flux capacitor. Definitely. It's in the middle, between the headrests and the trunk. Round thingy on top.

Does it happen all the time or just when you hit 88 mph?

Not too hard to find a replacement: https://www.oreillyauto.com/flux-capacitor
(Holiday season may affect availability.)
 

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Discussion Starter #6
Does the speedometer work ok or is it trying to go backwards too?
Speedometer operates fine, just the odo counts down, is it possible for the trans speedo drive gear to cause this? Maybe incorrect direction?
 

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The gears are helical (curved ) I think, and somebody installed the driven and the counter gear backwards.
 

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Didn’t have this issue but my miles were counting forward too fast. Just did a cluster resto and went through that thing and got a decent understanding of how it works.

Ended up getting a lightly used Odometer Speedo gauge that works fine. Old one was toast someone put the numbers together wrong. Both the old and new had proper speed readings by the needle verified against GPS. Check that with Waze.
But more then likely I’d bet if your speed is going forward than someone messed up the gears in the unit in dash. When I hooked up my cable and drill outside the car and gauge cluster I would NOT get any forward speed showing going in reverse. Miles went backwards. Thus it is less likely your gears in the tranny are wrong. But you should count the teeth on the end cable + make sure cable is lubed up. If you pull the Speedo you can quickly verify by spinning with a drill if it’s the problem. This is a lot of work though.
 

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Sorta sounds like the odo has been apart and not put back together correctly
I agree based on my observations of my old and replacement OEM unit. It could also be a China knock off and those are notoriously flaky ? I’ve seen photos of the gears drives and they are different than OEMs.
 

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Discussion Starter #12
Didn’t have this issue but my miles were counting forward too fast. Just did a cluster resto and went through that thing and got a decent understanding of how it works.

Ended up getting a lightly used Odometer Speedo gauge that works fine. Old one was toast someone put the numbers together wrong. Both the old and new had proper speed readings by the needle verified against GPS. Check that with Waze.
But more then likely I’d bet if your speed is going forward than someone messed up the gears in the unit in dash. When I hooked up my cable and drill outside the car and gauge cluster I would NOT get any forward speed showing going in reverse. Miles went backwards. Thus it is less likely your gears in the tranny are wrong. But you should count the teeth on the end cable + make sure cable is lubed up. If you pull the Speedo you can quickly verify by spinning with a drill if it’s the problem. This is a lot of work though.
I pulled the cluster out and took it apart, put a drill on the speedo and watched the odo, if I rotate it counter clockwise the mph moves correctly and the miles count down. Did the same thing on my 65 speedo and the odo moves normal, up. Weird thing is the gears that drive the odometer look like they are in the right spots and no damage.
 

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I pulled the cluster out and took it apart, put a drill on the speedo and watched the odo, if I rotate it counter clockwise the mph moves correctly and the miles count down. Did the same thing on my 65 speedo and the odo moves normal, up. Weird thing is the gears that drive the odometer look like they are in the right spots and no damage.
Dude, you are hell-a-fast ?

Well you likely found the issue. Was going to show you my odometer drive gears but 67-68 might Be a totally different unit than 65-66. But since you have your OE 65’ and the 66’ do they look the same? Was the 66 a rebuilt OE or is it a repro?

If you find the offending part maybe you can swap in from the old. But I’d send it out for repair unless you know what your doing in there. I found on my old unit the little wheels are harder to sort out than in the video. Or my unit was just so shot I was doing it right but it didn’t matter.
 

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Discussion Starter #14
Dude, you are hell-a-fast ?

Well you likely found the issue. Was going to show you my odometer drive gears but 67-68 might Be a totally different unit than 65-66. But since you have your OE 65’ and the 66’ do they look the same? Was the 66 a rebuilt OE or is it a repro?

If you find the offending part maybe you can swap in from the old. But I’d send it out for repair unless you know what your doing in there. I found on my old unit the little wheels are harder to sort out than in the video. Or my unit was just so shot I was doing it right but it didn’t matter.
Lol it’s bugging me and I’ve been messing with fitting it in the dash and wiring it up this week, so it came out real fast lol. The 66 cluster is a cleaned up OE unit, but I don’t see any damage to any of the gearing for the odo. The way it’s gears are stacked compared to the 65 is different so when you turn the speedo counterclockwise the 66 spins a different way than the 65, I don’t think the gears could be put in the wrong spots.
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I've never pulled one of these apart before, but it looks like the tall, slender plastic gears that are parallel to the the cable are on opposite sides of the odometer numbers shaft between the two assemblies (one in foreground, one in background). Or, is it possible the large, metal gear on the odometer numbers shaft needs to be mounted up against the tenths position? If possible to flip either, it will rotate the numbers shaft the opposite direction from how it is now.
 

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Yours is assembled wrong. Take a look at this picture and you will see that the long gear to the right is behind the odometer drive gear. Yours is not. Thats why it runs backwards.
740809
 

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Discussion Starter #17
Yours is assembled wrong. Take a look at this picture and you will see that the long gear to the right is behind the odometer drive gear. Yours is not. Thats why it runs backwards. View attachment 740809
The first pic is the 66 speedo, the gears are set up like the pic you provided, the second pic is the 65 speedo gears positioned differently then the 66. Here’s another pic of my 66 speedo
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There is only one 65/66 140 mph Mustang speedo. It's C5ZZ-17255-A. They were supplied by King Seeley
and they are all set up for CCW cable input.
If the speedo needle reads in the correct direction from counterclockwise input at the cable connection, but
the odometer turns backwards (counts down), the gears in the speedometer head driving the odo are wrong or improperly installed.
 
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Discussion Starter #19
the needle moves up in mph when spun CCW on both the 65 and 66 speedo, the gears in the 66 looked to be the original and not removed before I’m at a loss right now.
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