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Still trying to sort this out! Based on the trans and axle codes, it is a 3 speed overdrive (pardon my ignorance but it just has three speeds), and the trans ratio is 3.89.
I checked the speedo (thanks Chad), and the speedo and cable are fine, so the issue is with the speedo cable gear.
Pic: Scroll down to 3.89-1 with Borg-Warner 3 M/T with overdrive. Notice the original bias ply tire sizes.
Thanks Bill. Looks like I ordered correctly and got the 20 tooth gear. I just tried a cable gear with the teeth in the opposite angle, but no joy, so I now assume it has something to do with the speedometer drive gear being installed incorrectly, or the wrong drive gear. The teeth in mine are like /////, but perhaps they should be \\\\\. Part number from Bill's charts above is C2AZ-17285B, and its a steel gear unlike all the plastic ones that seem to be on offer. Surely someone has had this issue before.
The only book I have that shows a transmission that old is a 1964 Motors manual. And the only side loaded transmission that looks like yours is what they call a 57-62 type 10 and on the output shaft there is something called a drive ball that seems to be associated with the speedometer drive gear. Could it be that it's missing and your drive gear is just floating around on the shaft? I would look in there and see what that gear looks like and if it will rotate on the shaft. You might have to pull the tail shaft housing to know for sure what's going on in there. But from all the carnage I see going on with your cable and gears something isn't right in there.
Direction of rotation of the cable is otherwise determined by the direction of rotation of the transmission internals. Driven gear itself, unless there is some other part missing, wouldn't change direction of rotation by changing the pitch on the gear.
Thanks Crop Duster & Chad, if the needle wasn't registering a speed in forward or reverse, the drive gear may be floating around on the shaft as you suggest. However the drive gear doesn't feel loose at all, and because the needle indicates a speed in reverse, I'm coming to the conclusion that the drive gear may be incorrect. The analogy I'd use here is that it's like trying to trying to drive screw by turning the screwdriver in a counter-clockwise direction.
I will need to pull the tailshaft housing, but before doing so, I'd love to see a picture of the correct C2AZ-17285B drive gear highlighted in Bill's page scans, so I'd be most grateful if anyone can point me in the direction of such a pic.
On a somewhat related note, its strange that I could get a speed reading using both the //// and \\\\ gears I used, as I would have thought one would mesh with the drive teeth direction, and one would not. If this whole exercise was on a test, I would have failed.....
I think ND or Chad could help you out if they knew what that transmission came out of. Did the ID tag survive? If it did post those numbers. If not my Motors manual does mention a couple of specific vehicles that a transmission that looks like yours came in and that is a 1957 Thunderbird with a 292 V8, 62 Fairlane V8 and 62 Meteor V8.
The chart posted by number dummy indicates you need a steel driven gear, not the standard Ford Nylon gear. I doubt the nylon Ford driven gear is engaging the drive gear properly.
However, you may need to pull the tail shaft housing and make sure the drive gear is actually there, it is correct for your application, and that it isn't spinning on the tail shaft. It should have a helical cut gear since it is mounted near the centerline of the tail shaft, and it should have a RH rotation.
The Ford top loader 4 speed is the only one that had the speedometer gear enter on the passenger side requiring a LH rotation. The Ford manual 3 speed, the C4, C6 and AOD automatics and the NP 435 4 speed all use a RH rotation driven gear as they enter on the driver side. Early T85s used straight cut speedometer gears and the driven gear mounted at the bottom of, and perpendicular to the tail shaft, not at an angle.
The chart posted by number dummy indicates you need a steel driven gear, not the standard Ford Nylon gear. I doubt the nylon Ford driven gear is engaging the drive gear properly.
However, you may need to pull the tail shaft housing and make sure the drive gear is actually there, it is correct for your application, and that it isn't spinning on the tail shaft. It should have a helical cut gear since it is mounted near the centerline of the tail shaft, and it should have a RH rotation.
The Ford top loader 4 speed is the only one that had the speedometer gear enter on the passenger side requiring a LH rotation. The Ford manual 3 speed, the C4, C6 and AOD automatics and the NP 435 4 speed all use a RH rotation driven gear as they enter on the driver side. Early T85s used straight cut speedometer gears and the driven gear mounted at the bottom of, and perpendicular to the tail shaft, not at an angle.
Good info. My drive gear is there, it is steel and it's not spinning on the shaft. The driven gear is engaging properly with the drive gear as it reads steadily when driving in reverse (ie the needle doesn't jump around like it is engaging intermittently). I don't have the trans number, but will have a look for one when I see the pick-up on the weekend. The only question I have is whether the gear is correct for the trans. If the gear was removed and laid on a table and you looked at it side on, the threads would go from the top left to the bottom right which is causing the cable to spin clockwise, but it needs to spin counter-clockwise. If they went from the bottom left to top right I believe that would resolve the issue, but I'm keen to see the correct gear to confirm before I pull the end of the trans.
Here's a pic showing the drive gear through the speedometer cable hole in the trans.
You may be on to something. This the drive gear on a C6 transmission. The only clear depiction of a speedometer drive gear I could find in my books was a 4 speed top loader with the cable on the passenger side and it looked like your gear.
You may be on to something. This the drive gear on a C6 transmission. The only clear depiction of a speedometer drive gear I could find in my books was a 4 speed top loader with the cable on the passenger side and it looked like your gear.
1973 and later C4 & C6: The speedometer DRIVE gear is made as part of the output shaft.
Prior years (1966/72 cars & 1968/72 F100/350). The C6 DRIVE gear was available by itself, see pic below from 1964/72 truck catalog.
1973 and later C4 & C6: The speedometer DRIVE gear is made as part of the output shaft.
Prior years (1966/72 cars & 1968/72 F100/350). The C6 DRIVE gear was available by itself, see pic below from 1964/72 truck catalog
ND, do you have a part number for the drive gear on that transmission he has. From what I can find in a maintenance manual it might be the same one used behind a 1957 Thunderbird 292 V8. I just posted that picture to show the pitch on his gear is opposite to what you would think it should be. But unless he can find a tag on that transmission who knows what it came from.
ND, do you have a part number for the drive gear on that transmission he has. OP already has the part number.
From what I can find in a maintenance manual it might be the same one used behind a 1957 Thunderbird 292 V8. I just posted that picture to show the pitch on his gear is opposite to what you would think it should be. But unless he can find a tag on that transmission who knows what it came from.
Pic of parts catalog I posted in post #18 lists C2AZ-17285-A 7T steel DRIVE gear for the OP's application (3.89-1 3 M/T with Overdrive).
C2AZ-17285-A replaced B7A-17285-D = 1957 Fairlane with Overdrive, 1957 Thunderbird with Ford-O-Matic; 1958/60 Thunderbird 352 with Overdrive + another 20 or so 1957/59 applications.
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I can't believe its taken this long for a comment like that 
