Speedometer / speedometer drive gear

Brianfrench65

Brianfrench65

Well-known member
I have been fighting with speedometer problems, since I bought this car 18 months ago.

I found the 19 tooth gear with several broken teeth. I removed the broken tooth pieces, and replaced the gear, and I also changed the speedometer. It all worked for 99 miles. I then found the housing (turtle) cracked. I had missed a broken tooth. I replaced the entire assembly, and I put the original speedometer back, and it all worked for 104 miles.

Now I have another broken gear, 3 teeth broken.

The speedometer cable is new, and very well lubricated with graphite. The speedometer works perfect by attaching a drill to the turtle end, running backwards.

What am I missing? Please.

Thank You;
 
The housings aren't all the same. Try it for fit to the driveshaft with no gasket, and see if it rocks a little. Some guys have stacked gaskets to lift the housing, if it's too tight to the driveshaft gear.
 
You may have an issue (to much play) in the drive shaft bearing and sleeve. This allows movement of the drive shaft putting to much pressure on the driven gear and turtle. Sometimes adding gaskets to the turtle (shimming it away) will help eliminate some of the pressure on the gear. Adding gaskets can also cause an issue when the gear drifts away from the turtle assy...
 
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Tom Wesenberg said:
The housings aren't all the same. Try it for fit to the driveshaft with no gasket, and see if it rocks a little. Some guys have stacked gaskets to lift the housing, if it's too tight to the driveshaft gear.
Click to expand...

Tom; thank you. I did check the fit, without the gasket, and used a 3/16" square key ( key stock), and there was a bit of slop in the gear. When I put it together, I used 2 gaskets. I filled the housing with 600 W gear oil. The housing was still full of oil, when I took it down.

The speedometer cable has both support clamps in place (chassis over muffler, and firewall).

I am perplexed.

Thank You;
 
Is It possible that the worm gear, that's been cut into the driveshaft is some way buggered up and chewing up the gears in the turtles?. Just wondering!
Terry
 
I would remove the gear housing and use a screwdriver to push the driveshaft up and down to check for freeplay like Mitch mentioned. I wonder if the gear has too much clearance, and the teeth are riding up on each other.
 
Thank you all for your suggestions.

I was just wondering if I should try an 18 tooth gear? It will be a smaller diameter, and less accurate, however better than "0" .

When I bought the car I did count the tooth positions, and there were 19. The housing also had the raised "19" on the casting.

As far as I know, I have a standard drivetrain, and I do have 19" wheels.

Thank You;
 

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I tried the 18 tooth gear in the stock housing for an overdrive set up for a late '31 with 3.78 rear end. The smaller diameter wouldn't engage the driveshaft gear properly even without the gasket but not sure exactly why.
Check other issues as stated by others. Can the driveshaft gear be installed in the reverse position, i.e., rotate 180 deg? Some other posts may have touched on this
 
Well.....when I really look at the 19 tooth gears, it looks (to me), that the gear is Bailey engaged, and possibly the gear is riding up on the drive shaft gear. When I push up on the drive shaft gear, it does not seam to move up at all (car in neutral).

Any additional comments are certainly welcomed.

Thank You;
 

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Tom Wesenberg said:
I would remove the gear housing and use a screwdriver to push the driveshaft up and down to check for freeplay like Mitch mentioned. I wonder if the gear has too much clearance, and the teeth are riding up on each other.
Click to expand...

Tom; after studying the failed gears, I do believe you are correct "and the teeth are riding up on each other".

So.....do I put another new gear in, and assemble without a gasket? A skim of form-a-gasket?

Any suggestions are greatly appreciated.

Thank You;
 
Brian: attached is a photo I rec'd of the drive gear position, if that helps.Hopefully this matches with yours.
 

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Duke; I can't seem to get any, by pushing up with a screwdriver (transmission in neutral). Maybe a slight movement, but I really can't find any.

Thank You;
 
Does the gear on the driveshaft slide along it some? Mine slides about 1/4" and am told the turtle and small gear keeps it in position. Perhaps you could jack the rear end and see how the drive shaft gear is behaving without the turtle attached .
 
I would spin the gear as you slowly lay it against the driveshaft. As soon as you can't spin the gear see how much distance you have to seat the housing. This will be the amount of teeth engagement. Maybe you need a different housing that lets the gear engage more.
 
Tom Wesenberg said:
I would spin the gear as you slowly lay it against the driveshaft. As soon as you can't spin the gear see how much distance you have to seat the housing. This will be the amount of teeth engagement. Maybe you need a different housing that lets the gear engage more.
Click to expand...

Tom; I think that you are correct, however trying 3) different housings, all seem to be the same. I am just about seated, before I feel the gears meshing (using a piece of 3/16" square stoch in the square cable hole). Without any gasket, it still feels like, only slight engagement.

One of the housings I tried, I think is an original.

Thank You;
 

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