Speedometer gear ? 49 3 speed with OD

1949mercury

1949mercury

Senior Member
I need to put my speedometer gear in, how does this work ? I put it in the hole and it seems like I could put it all the way in and it would just fall inside. I put it in the cable then put the cable inside the transmission but it seems like it could fall out inside the transmission. What holds the gear from just falling inside the transmission and damaging something ?
 
First you will need to know that there is a driving gear on the output shaft inside the transmission. The next thing is whether you know that you have the overdrive driven gear and cable assembly that were made for the overdrive transmission or not. The non-overdrive transmission had different parts. You need the 8L-17262-A cable for the 1949 unless the transmission has been changed. This cable was also used in the Lincoln cars in 1949. You also need the correct gear to match up with the rear axle ratio you have in the car. The gear just snaps into the cable then the whole thing is inserted into the transmission and secured with the cap screw that holds it all.


The gear has a integral piece that holds the gear in place. I'll have to look at my 51 stuff so that I can accurately describe it since it's been a while from the last time I had to put one in. The 49 may be different though but I'm not sure.
 
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I have the stock cable and transmission. I had the transmission gone through just to make sure it was all in good working order when I finally got the car going. I found a 22 tooth speedo gear in my box of stuff. The gear fit in the cable snug just didn’t snap in there. I’m not sure about the gear inside the transmission I can put my finger in there and don’t feel much. I did put the gear in the cable and put the cable on the transmission I’m just worried it will fall inside after driving it for awhile.
 
I checked one of the cable assemblies I have from an early 1951 (uses same basic transmission as the 49 & 50). The plastic gear has an groove like a C ring would fit into on its shaft but no C-ring so I can't say that they have one until I see one. I felt into the port and there is a raised flat shelf part of the casting inside there that guards the gear from coming out any farther than is required for a good mesh. Rotation may also help thrust it toward the cable housing in operation but I'm not sure enough to say other than that is a good possibility. If the gear tries to go downward by gravity, it has a center nub that will ride on the cast shelf and arrest further movement. The cable housing has a rather large end that fits snug in the casting so it shouldn't move around much at all. There is also an O-ring to seal it to the housing as well.

If what I describe fits what you have then you should be safe to install it back in there. Put a little dab grease on the gear shaft to hold it in place for installation and you should be OK.
 
Ok thanks I didn’t see anything in the manual for a C clip, the shaft on the gear did have a couple groves around it that spiral. I’m thinking once it starts spinning it should stay in like your talking. When I drive it next I will see if it works. Getting my rear window and wiring put in next week. Then some new tires.
 
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There is no break down on it in the parts book and very little info in the Lincoln Mercury O/H manual about it either. The spiral cut acts to keep oil in the transmission where it belongs. The groove may also fit a small O-ring but I can't tell you for certain. It should be fine the way it is.
 
Hard to put into words, what holds it is a flat round spring steel band with a ridge
that goes on the gear - gear is slid onto the cable housing the ridge on the band
snaps into the slit on the cable housing kind of a cir clip. Not sure if this was used
on OD trans or even those years. I have a overdrive 49 or 50 I'll check if its got a
cable on it & look at the gear....sam
 
The Mercury OD transmissions have a small gear near 1-inch in diameter pressed on to a little steel shaft that is near 1 1/2-inch long and around 3/8-inch in diameter in the middle part with the square drive formed into a stepped down diameter on the end opposite the gear. Some were all metal and some have a plastic gear. The tooth count number is on the gear. The gear shaft is slid into the cable casing end piece that actually fits the bore of the transmission tail shaft case. The cable casing end piece is held in place by a metal fixing piece that bolts to the case with a single small hex head cap screw.

I've worked on accessories for turbine engines that have a shaft held in place with a small spring steel C-ring in a groove but they were spline type shafts so there was no rotation between the shaft and the inner rotor that it fit into. In this case the speedo gear shaft rotates inside the cable end piece. My other car is up in Kansas so I can't look at it to confirm anything about a part that might help hold the shaft inside the end piece but I'll keep looking to see if I can find any information on the subject.
 
Ok thanks I would like some more information if you can find any. Everything you have described is exactly how mine is I’m just not sure what is inside the transmission.
 
The base number for the gears is 17322. The Mercury cars had 8M-17322 with suffix to indicate the ratio tooth count needed. The information is in the Mercury parts books under Speedometer in the 8M-17255 number range but the only illustrations are for the cable & cable housing assemblies since there are different lengths & styles depending on the year and body type and those are only in the later 49 to 52 or 49 to 53 parts catalogs. The Chart for the cable & casing assembly indicates that the 1949 models had no O-ring on the part that fits into the transmission so that is the only major difference. They are otherwise interchangeable with ones that do as long as the length & fit are the same or very close to the same.

I looked at a lot of speedometer driven gears on Google but couldn't find any with the 1949 thru early 1951 numbers. Many others have a groove in the shaft but nothing is in it. The one I have here was run that way for a long time with no apparent problems. I can feel the drive gear inside mine when I put my finger in there and I can also feel the ledge or step in there that acts as a stop for the gear so it can go no further.

I found this link to one labeled for British Ford but it looks just like the Mercury ones for the most part and it has the C-ring or spring ring whatever you choose to call it but the ring just holds it till it's installed. https://www.ebay.com/itm/NOS-1950-6...683948&hash=item4642feff8f:g:kqIAAOSwHjNWAa~T
 
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Ok that’s a little concerning because when I stick my finger in the hole I can’t feel any gears or stop. I can put the gear in the hole and twist it and it doesn’t grab on to anything or another gear and I could push it all the way inside the transmission and probably loose it if I let go.
 
There is a governor port and a speedometer port on the rear housing. I would have to have photos of what you have there to help further. The 49 transmission was basically the same through early in the 1951 model year. Unless you have something different or parts are missing. Your tail housing should be similar to the one in this link.
http://www.vanpeltsales.com/FH_web/FH_images/FH_trans-pics/Flathead_Trans_49-50merc-od.jpg

Even though this link is for a standard 3-speed, your case should be similar in external appearance.
http://www.vanpeltsales.com/FH_web/FH_images/FH_trans-pics/Flathead_Trans_49-50merc-3speed.jpg

The drive gear on the output shaft has to be in there or the governor won't work either. It is above the location of the speedo gear port. Following the angle of the port, the step in the case is just below where the speedo driven gear would be if it was in there and straight above that is the drive gear.

If you have a Ford car transmission or something else then it's not the same set up.
 
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Mine looks just like the OD picture in the link. It is the stock transmission and I took it in to have it rebuilt /gone through a few years ago so when I did put it in the car it was all ready to go. I guess I should get under there and look in the port with a flashlight and see what’s in there
 
1949mercury said:
I need to put my speedometer gear in, how does this work ? I put it in the hole and it seems like I could put it all the way in and it would just fall inside. I put it in the cable then put the cable inside the transmission but it seems like it could fall out inside the transmission. What holds the gear from just falling inside the transmission and damaging something ?
Click to expand...


The teeth on the speedometer gear should come in contact with the spiral threads on the O/D output shaft. The port on the O/D tailshaft housing tilts downward at a slight angle which puts the teeth on the gear in contact with the output shaft slightly below the centerline of the shaft and when the housing on the end of the speedometer cable is bolted in place the speedometer gear is held in that position - it can't go past the output shaft. As I recall I used bearing lube to hold the gear in the speedometer cable housing while inserting it in the port. Photos of the cable housing are attached. I assume that you are using the same speedometer cable.
 

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A followup thought. I can’t find a photo of the plastic speedometer gear that ‘s in the trans on the truck but as I recall the the edges of the teeth on the gear were a little concave. I bought it used so I can’t say whether that was from wear or it was made that way. At the time I bought it those gears were scarcer than hens teeth and was told that the gear was unique to the 49-51 Merc O/D transmissions, maybe because of the oddball 4.27 differential ratio.
 
The oddball ratios are the ones that are generally easy to find in old Fold parts house stashes since no one needed them as much. The 20 tooth gear is likely the most common and that would be for the overdrive ratio 3.91:1 or 3.92:1 used in Dana 41 & Dana 44 axles. The speedometer gears are set up more like a worm screw set up. The driven gear has a slight angle to the teeth but there isn't any noticeable curvature to the teeth on the ones I have. The drive gear is more like a worm screw. It has the 7 teeth spiraling around the circumference a good bit. Even the old Ford transmissions had a 7-tooth gear.
 
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