Community Q&A Question: Speedometer still 10mph off.

Asking About: Mustang 23 Tooth Speedometer Gear & Clip Kit (83-95)


Speedometer still 10mph off.

I have a 1991 LX 5.0 w/AOD transmission and I installed a 4.10 rear end, so I purchased this gear along with a new speedo cable (I had the jumpy speedo problem) and while it (mostly) cured the jumping problem, the speedo is still off by 10mph. Why? Also anyone know why the speedo would still be a little jumpy? It's only jumping 2-4mph it's still happy.
from Apple Valley |
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It's still happening * auto correct ftl - Timothy 3 years ago

Also my tire size is 225/55/16 - Timothy 3 years ago
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Because you have a 91 with an AOD, the internal drive gear in the transmission is an 8 tooth unit. Even with a 23 tooth driven gear, you will be 10mph off with 4.10 gears. Without a custom reduction box form someone like Abbott, this will be as close as you'll get.

Jumpy speedometers are typically an old/worn cable, a new cable that was not properly lubricated, or a defective speedometer itself.
from Hewitt |
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Aww that sucks... Oh well. At least I got it fixed. I know probably lubed the cable, I pushed the cable slowly through the sleeve and let the graphite lubricant run on it as I slid it in, then poured a little down the sleeve after the cable was in for good measure. I think it might be my cluster. Thanks for the quick response though, I'm impressed by how fast I was responded to! - Timothy 3 years ago
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Your magnet in the speedo itself could be broken. For speedo repairs contact One warning if you remove the cluster, don't drive the car! The charging system won't work because the removal of the volt meter breaks the circuit from the alternator to the battery.

Otherwise, for speedo correction, did you use the calculator?
from Brownstown |
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Yes I did, but I didn't know my AOD had 8-tooth drive gear, I thought it was 7. I still don't regret the purchase, at least my speedo is only 10mph off, I don't even want to imagine how far it would be off with the gear that's for a 2.73 rear end! (what I had previously). - Timothy 3 years ago
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