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  • 1 Post By Unique427
  • 1 Post By ERA174
  • 1 Post By twobjshelbys
  • 1 Post By ERA174
  • 1 Post By Blas

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  #1 (permalink)  
Old 04-21-2022, 03:36 PM
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Default Speedometer driven gear issue

I have a "big input" close ratio toploader in my Superformance with a Robert Pond aluminum 427. I got this car in December and the speedometer was off. It reads about 10mph slow. I got on the web and found the formula to figure out which gears I need and was able to determine that I needed a 16 tooth driven gear. The car had a 21 tooth installed when I got it. Seemed like a legit finding so I ordered the gear.
I saw where the toploader had a different set of gears for the Galaxies. Seems they have a cable assembly that enters the tail housing on the drivers side and require gears that are slanted opposite of the ones that go in the passenger or right side.
My trans has the cable entering on the right or passenger side so I ordered the driven gear accordingly. Mine has a 6 tooth beige colored {probably discolored white} on the output shaft. Upon initial inspection it appeared to be fine and by the chart I saw also appeared to be the correct gear.
I got my new gear, installed it and it did seem to be reading the speed correctly. However, about 1/2 mile worth of driving and the speedometer ceased to read. I pulled the gear and you can see in the photo below that it is wiped out. It also appears to be slanted differently than the 21 tooth red gear I had. The red gear did operate the speedometer, just not accurately.
Not sure now if the new gear is incorrect. My problem is that every photo I see of a driven gear for a right side cabled toploader slants just like the white gear that failed. Doesn't seem right to me that you could have the left side cabled gear in a right side transmission and just install the other gear and have it work.....someone out there has to know what I have here....any help or info is greatly appreciated and as always, thanks in advance !!!!!!

Edit: sorry, I forgot to attach the photo
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Old 04-22-2022, 09:32 AM
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There are left and right-hand gears used depending on which side
the transmission the gear attachment point is. Looks like you got
them mixed and it committed seppuku (took its own life).

Re-order a new gear with same groove direction as original.

Here's some additional reference material if interested:

http://429mustangcougarinfo.50megs.com/speedo_gears.htm
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Last edited by Unique427; 04-22-2022 at 09:34 AM..
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Old 04-22-2022, 12:29 PM
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It appears you originally had a RH(right hand) 21 tooth driven gear, not sure why given your passenger side speedometer cable placement. The replacement 16 tooth driven gear you installed has LH(left hand) teeth, not a match as you discovered. I believe the correct replacement RH 16 tooth driven gear is Ford# CODZ-17271-A. You should check the teeth on the drive gear to make sure they have not been damaged by the LH 16 tooth driven gear. Shining a light in the hole of the tail shaft housing for the speedometer cable and rotating the output shaft should be sufficient for inspection. If the drive gear looks ok, replacing the driven gear with the part number I supplied should work. If the drive gear has significant damage the tail shaft housing will have to be removed to replace it. Depending on how severely the gears were damaged, you should probably also replace the transmission lube to eliminate as much of the plastic gear debris as possible.
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Old 04-22-2022, 01:39 PM
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I've seen gears stripped if the drive gear and driven gear are swapped or two of the same installed.
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Old 04-23-2022, 05:13 AM
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Quote:
Originally Posted by ERA174 View Post
It appears you originally had a RH(right hand) 21 tooth driven gear, not sure why given your passenger side speedometer cable placement. The replacement 16 tooth driven gear you installed has LH(left hand) teeth, not a match as you discovered. I believe the correct replacement RH 16 tooth driven gear is Ford# CODZ-17271-A. You should check the teeth on the drive gear to make sure they have not been damaged by the LH 16 tooth driven gear. Shining a light in the hole of the tail shaft housing for the speedometer cable and rotating the output shaft should be sufficient for inspection. If the drive gear looks ok, replacing the driven gear with the part number I supplied should work. If the drive gear has significant damage the tail shaft housing will have to be removed to replace it. Depending on how severely the gears were damaged, you should probably also replace the transmission lube to eliminate as much of the plastic gear debris as possible.
What doesn't make sense in this case is that the drive gear appears to be the correct one. I can see it is pink, 6 tooth and undamaged. This means that the red 21 tooth driven gear with it's right hand gearing was incorrect from the start. However, it worked and read speed just fine, albeit wrong/slow by 10mph. A close look at the red gear shows slight damage but I still don't understand how it could have worked at all if the drive gear is in fact left hand. I can only see it with an inspection mirror. it is definitely pink and absolutely 6 tooth as it should be. It is my understanding that the 6 tooth pink gear is left hand. I have ordered both the drive and driven gears new and will find out for sure what's going on when I pull that tail housing. Thanks to everyone for the info!!!!! It is greatly appreciated!!!!
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Old 04-23-2022, 12:46 PM
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Default Toploader Speedometer Cable Gears

The following image depicts the correct gears for your application. I'm curious to see what drive gear is installed on your output shaft now.

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Old 05-13-2022, 02:52 PM
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Sorry for the delay fellas in getting back to this post.....just yesterday I jacked her up and removed the tail shaft housing so I could install new gears. I installed a black 7 tooth right entry cable drive gear on the output shaft and another new drive gear on the cable. This time it lasted a little longer...I got about a mile and a half out of it before the speedometer quit reading and went to zero.
I kind of knew that the 16 tooth driven gear would read a little high and it did, but at this point I just wanted to make sure it would work. The plan was if it worked and read and didn't fail I would worry about the correct tooth driven gear later. As above, it didn't quite work out that way.
Initially, when I first got the car it read slow but the needle was smooth and consistent and it read something, even if it was off. The second try {this is try #3} when I just changed the driven gear it read dead on and was smooth, but only for about 1/2 of a mile or so. On the second try it damaged the drive gear also, so I ordered both gears new. Try #3 lasted a little longer and read a little high, but it also did something else the entire mile and a half, before it failed...the needle on the speedometer had a steady bounce.
One thing I noticed on try number 2 that I didn't think anything of until after it quit, was that the driven gear seemed to need the cable pushed in a little in order to get the clip on it. Looking back, it was as if the inside cable was a little too long for the jacket. So, this time I took a Dremel and removed about 1/8" off the end of the cable. The gear went on zero problems, the clip went on no problem and the gear and cable turned by hand very smooth. I really thought I had it this time until I saw that needle bouncing.
I am lost...the cable turns very smooth, the speedometer reads until the gear strips and the gears go right together and seem to mesh just fine. I would like to have a working accurate speedometer and this just isn't rocket surgery....but it's enough of a job pulling that tail shaft that I wont do it again until I have a smoking gun. Any suggestions or ideas are greatly appreciated. I have photos of the recent gears, but they really look the same as the first ones. I will post if anyone wants to see. Also, the only thing "different" about this set up from others I have worked on {not a speedometer expert, but this aint my first rodeo either...} is that the toploader was put together without the factory gasket between the main housing and the tail shaft housing. That would change the relationship of the drive to driven gear, but that little bit hardly seems like enough to destroy gears this quickly....1/16" or less???
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Old 05-14-2022, 02:40 PM
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Any possibility that your Speedo cable had been replaced at some point in time and the replacement cable is wound in the wrong direction causing binding and increasing the twisting resistance and stripping the plastic gears.?
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Old 05-14-2022, 04:04 PM
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ms,

There's an exploded view of a toploader here: Exploded View of a Toploader

In looking at it, it does appear quite possible that the two gears could be misaligned enough to cause your problem. The drive gear's position is fixed - it appears - to the output shaft. If the tailshaft housing (item #65) was moved 1/16" toward the front of the car by omitting the gasket (item #69), the driven gear (not shown but is mounted inside the housing) would be misaligned with the drive gear (item #37) by the same amount.

There's also a very nice cutaway photo of the drive/driven gears here: Cutaway View

It isn't obvious from the picture, though, whether a little misalignment would cause the gear to strip.

Maybe a picture of the stripped gear up close might help.

Just FYI,

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