Speedodrive Gears

A Brit trying hard to solve these old American car issues in a foreign land:-
My '57 Retractable with Ford-o-matic transmission has badly fluctuating speedo needle and only goes to circa 35 mph max. I have refurbished the speedo head and given it a new cable - and spinning bottom of cable in situ confirms that everything 'above' the drive/driven gear interface at transmission tailshaft is perfectly OK. Problem is clearly at this location. Rear axle ratio is 3.10:1 and the driven gear on bottom of cable is 19 tooth version with only slightly worn tooth profile. The square end of the cable fits snugly into the mating female square hole in the gear and there is no slippage between them. Tyre size is 215/75 x 14.
Does anyone know what the correct pairing of drive/driven gears should be for this car and where I might purchase a new pair.
Many thanks
kirky2

MacsAutoParts.com is a good place to start. They have the parts you are looking for. You can order online or call them at (877)283-6920.

Gary.

If your speedometer will only go to 35 mph, you probably have a problem with the speedometer head. The speedometer gears only makes small changes.
I would hook a working speedometer head to the cable under the dash and see if that ones reads correct, if it does you know the problem is in the gauge itself, if it reads the same (35mpg) the problem is in the drive gear in the transmission not the gear on the cable.
You can test the speedometer in place with a drill and short piece of cable, its not easy but is easier than removing the whole speedometer.

Quote:

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Originally Posted by goob

MacsAutoParts.com is a good place to start. They have the parts you are looking for. You can order online or call them at (877)283-6920.

Gary.

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Thanks Gary. I notice that Mac's offer a selection of gears with various teeth but I need to know what the specified driven/ drive gear pairing should be for my car. (I don't see any tailshaft drive gears mentioned). I understand what can happen is that when the flexible cable is withdrawn from the transmission tailshaft, on occasions the gear is not retained on the end of the flexible and falls into the tailshaft housing and is unretrievable. I cannot see inside the transmission when in situ to see anything. It could be that a previous 'incident' has caused a loose driven gear to have minced the drive gear on the tailshaft. (I suspect the drive gear is also plastic). Before I take the tailshaft housing off to investigate, I need to obtain THE CORRECT PAIR of gears to effect a speedy repair. Does anybody know what the correct 'set' should be?
Many Thanks.
JK

Hi Ford Only
As I felt I had explained, after dismantling the speedohead, cleaning, rebuilding and refitting and connecting up a new cable, I verified that the 'system' thus far was 'fine' by spinning the bottom end of the cable from under the car with an electric drill and got good steady readings up to circa 90 mph. The problem lies at the interface twixt cable bottom (driven) gear and 'drive' gear on transmission tail shaft. I suspect they are not engaging properly and would like to know what the correct pairing is for my spec. car so that I can have them to hand when I dismantle transmission to do the repair to avoid long off-road delay.
Somewhere that information should be available, surely??? - but I don't know where to look.
Many Thanks
JK

OK, I understand what you got going on but probably can't help.
I think the drive gear inside the transmission is steel and may be part of the rear shaft, I haven't had one apart in years.
You may want to just order a new gear and see if that will work, 19 to 20 teeth sounds about right.
The gear you have may be for a earlier Fordomatic and there not the same as what was used in 1957, I think that you need a gear with a right hand cut.
I would think that some of the venders that sell the gears would know what they fit. Have you called Jerry Miller restorations.
Good Luck

Most 57Skyliners had 3.56 rears w/Fordo.
Drive gear is 8 tooth
Driven 20 tooth- C0AA-17271-G Orange in color
If 3.10 18 tooth -C0AA-17271-J Natural "" ""

Goodluck,

Ron.

Hi SkylinerRon
This helpful - Thanks. Does what you say mean that, by some clever FORD engineering, an 8 tooth DRIVE gear on the tailshaft of the transmission can be used with EITHER an 18 tooth DRIVEN gear for 3.10 ratio axles OR a 20 tooth DRIVEN gear for 3.56 ratio axles??? If so, how interesting! I confess I was wondering if this was possible since traditionally all gears generally come in MATCHED PAIRS, I guess.
Many Thanks
JK

Hi All.
An endoscope inspection in situ of gear on transmission shaft revealed a blue gear (6 tooth?) appearing to be quite worn despite the poor resolution with the viewer. A comprehensive internet search revealed that no new ones seem to be available and used ones are VERY rare and difficult to obtain. Fitting a new 18 tooth DRIVEN gear has given me a properly functioning speedo for the moment (the engagement of the two gears must be quite small compared with new specifications). So OK for now. Perhaps this would be good project for a 3D printer working in nylon or acetal resin if the number of DRIVE gears required nationwide could justify the outlay. Just a thought . Anyway - Thanks to all for you contributions.
kirky2