Lazy speedometer

[Ricosan]

My speedometer is registering way off the actual speed. This morning I went for a ride and turned on the GPS speedometer I downloaded earlier this morning..
My speedometer registers a speed about 35% lower than actual.
It has a new cable I installed yesterday.

The cable is hooked straight to the back of the speedometer and then to the turtle on the torque tube. The speed indicating arrow is very smooth and steady.

Richard

[TJ]

If the cable change came about because the speedometer didn't work when you got the car, I suspect the gear in the turtle is wrong.

[deuce lover]

Its not the cable.Maybe the turtle or have the speedo serviced and calibrated.

[Ricosan]

This just occurred to me. In my initial description of my malady I didn’t mention that it has a Columbia OD. I removed the speed ratio thing that goes between the speedometer and the cable because it is binding up. I thought I would have a regular speedometer then. I’m new to columbias. Maybe some reason it’s showing such incorrect readings.

Richard

[ford38v8]

Your Speedo should then be accurate until you engage the Columbia.

[glennpm]

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Originally Posted by Ricosan

I removed the speed ratio thing that goes between the speedometer and the cable because it is binding up.

Richard

Richard, take the SW speedometer transmission apart and give it a proper cleaning and grease job.

Glenn

[Ricosan]

TJ, the speedometer worked when I took delivery back in January but the numbers were questionable even then. It worked for about 50 miles.
Deuce lover, it may turn out that this is the wrong turtle. No markings on the turtle that I can make out in the photo.
Ford38V8, that’s what I thought too. Is this a special ratio just for Columbia OD?
Glenn, yea, I think it’s time to take it apart. I’m a little concerned about the gasket.

Richard

[glennpm]

Richard,

I know that John Connely, https://www.columbiatwospeedparts.com/index.cfm carries them.

You may be able to save the gasket on now but it is just thin paper. You could make a paper one yourself or apply a thin coat on RTV blue gasket maker with a touch up brush for example.

Glenn

[TJ]

I saw your other post and that is one nice woody. It could be the car is already in the overdrive mode and that would cause the difference in the speedometer reading because you removed the unit that makes the change in the speedo and it is now hooked up direct.

[Ricosan]

Glenn, tomorrow I’ll take it apart and see what’s going on. I’m going to call John Connelly and see what he says.
TJ, thanks for the compliment. I’m thinking that the ratio for the turtle must be directly connected to the SW speedometer transmission. I’m going to call John Connelly tomorrow and see if he can shed some light on it.

Richard

[glennpm]

Hi Richard,

If your speedometer is being "lazy" when you have the Columbia engaged, then it is reading correctly just like TJ said above. The speedo would read 28.5% lower than actual. Remember that the axle and then the "turtle" will indicate a slower road speed since the Columbia rearend is gearing the axle to rotate faster than the axle input rotational speed. Make sense to you?

Glenn

[Terry,OH]

If the new speedo cable is running directly from the speedo to the turtle then the speedo will regester about 27% low when your Columbia is in high. You need the Columbia speedo gear ratio changer at the back of the speedo to correct the reading.

[Ricosan]

Hey Guys,
I’m beginning to understand. It looks like this turtle ratio is correct for the Columbia only. It requires the speedometer transmission to provide correct readings in non overdrive and overdrive?
I’m heading out to the garage now to take the speedometer transmission apart and clean ad lubricant.
Richard

[glennpm]

Yes Richard, speedometer will be correct when you are NOT in overdrive. SW transmission makes the difference when in OD.


Glenn

[Ricosan]

I’ve run into a problem. I can’t get the case to come apart. I’ve been pulling on it to take apart but it won’t move past this point. Is there something besides the 4 machine screws holding it together?

Richard

[glennpm]

Nothing else holds it in place. Try moving the flapper/actuator a bit. You may have to pry it carefully in several places in the gap with a thin piece of plastic for example.

[glennpm]

This is one of pictures I posted of mine in your other Columbia thread. Mine is the 37-41 transmission.

[Ricosan]

Success! I got it apart using a plastic knife. I was even able to save the gasket. I cleaned it and filled 1/2 with gear oil and put it back together. It didn’t work so I took it apart again and discovered I had a piece out of place. I put it back together and it will spin by hand.
I’ll be installing it as soon as I can.

[glennpm]

Great job Richard!

Plastic knifes and these mixing sticks for epoxy are great for jobs like this.


https://tinyurl.com/2p9fraea


Glenn

[Terry,OH]

The speedometer turtle is usually considered the device mounted on the torque tube. The speedometer cable attaches to it at the torque tube end and is considered a turtle due to it's unique shape. Fords name for this part is speedometer "Gear and Cap". Ford offered the turtles in different gearing. Their gearing has to match the vehicle rear differential gear ratio and the vehicle tire size for the vehicles speedometer to read correctly without the Columbia.

Many aftermarket Ford supply houses offer reprints of installation instructions and there is also a parts list for the Columbia. They can be very handy.
Your car appears very nice!

[Ricosan]

OK, I hooked the transmission up to the back of the speedometer and checked it to see if the gears would work, the cable would turn about 1 revolution and then lock up. It did the same on the other side.
I took the transmission out. On the bench it will turn freely in either gear position. I put it back on and held it back about 3/16” from snug up against the speedometer and it was still locking up.
Am I possibly missing a part? I just have the transmission and the pin that joins them. I don’t understand why tightening should have any effect on the gears.
Ideas?.

Richard

[glennpm]

Hi Richard,


Boy I don't know. My transmission is difference with speedometer cables in and out of it. Can you take closeup pictures of the speedo connection end of your transmission?


Glenn

[glennpm]

Part #B-38 is called a "key". It would slide into the speedo, part #B-37, end of your unit and the other end would slide into the back of your speedometer. This key would have the same square dimensions as the end of a speedometer cable and you could make one. What do you have?

[Ricosan]

I spoke to John Connelly this afternoon. He said that most of these SW were made for use in a trucks and the were calibrated for such. He wants me to send the transmission to him. I think it’s a good idea. I’m sure he will figure out the problem.
I’ll post an update as soon as I get it back.

Richard

[Ricosan]

Hey Guys,

I got my speedometer transmission back from John Connelly. I installed it and the speedometer now works and will indicate speed…but it’s the wrong speed. At around 45mph, it shows about 10 mph difference in speedometer speed from actual speed. This is the same reading I get when I bypass the transmission at the back of the speedometer.
I’m thinking that the transmission may be hooked up backwards (upside down). I have the actuating arm on the bottom?

It may be my imagination, but it doesn’t seem to change the speedometer speed when I shift into overdrive. I am going to disconnect the arm from the OD shaft and try engaging with my hand.

Richard

[glennpm]

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Hi Richard,

If the speed is identical with the Columbia engaged or not, this tells me that the SW speedometer tranny is doing its job correctly. Your turtle may be the wrong one, explaining the error.

On the attached page from the Green Book, find your rear axle on the top row and then select the column marked "NO. TEETH". These refer to the number of teeth in the turtle. The tooth count is cast with raised characters on the turtle.

[V8COOPMAN]

Originally Posted by Ricosan

It may be my imagination, but it doesn’t seem to change the speedometer speed when I shift into overdrive. I am going to disconnect the arm from the OD shaft and try engaging with my hand.

Richard

Richard.....Unless I am mis-understanding, WHY would the SPEEDOMETER SPEED (vehicle speed) change when you shift into O/D? At the time you shift to O/D, the vehicle is STILL only traveling at the SAME speed as before making the shift.

Coop

.

[glennpm]

It will be the same indicated speed with or without overdrive if the SW tranny is working as it appears to be now.

Glenn

[V8COOPMAN]

Originally Posted by glennpm

It will be the same indicated speed with or without overdrive if the SW tranny is working as it appears to be now.

Glenn

Sooo.....Does that mean I'm correct, or that I'm full of it as usual?

Coop

.

[Ricosan]

OK, I see what you are saying. I don’t know what i was thinking! I need to get the right turtle to register the right speed.
Looking at my turtle, it doesn’t seem to have any numbers stamped on it.
Glenn, for some reason I can’t download that chart here on my iPad. I’ll see if I can on my computer.
Richard

[glennpm]

Originally Posted by V8COOPMAN

Sooo.....Does that mean I'm correct, or that I'm full of it as usual?

Coop

.

Coop gets an A+ :-)
You are correct.

[glennpm]

and here is a jpg of the pdf page.



Just for 1933
Please ignore the yellow highlighting which is for my 32 with 40 rear.

[glennpm]

Turtle for a 21 tooth gear.

[Ricosan]

Here is what I have.

[glennpm]

Yeah, unreadable.

Are you reading 10 MPH high or low at 45 MPH with your software?
Do you know the ratio of your rearend?
Tire sizes original 5.50 X 17"?

You can also unbolt the turtle and count the teeth Richard.

[Kube]

Originally Posted by glennpm

This is one of pictures I posted of mine in your other Columbia thread. Mine is the 37-41 transmission.

This is 1940 +.
Earlier are much different.

[Ricosan]

Glenn, yea 5.50 X 17 and I don’t know what the rear end ratio is. It feels like a 411.
Kube, that’s the exact same transmission as i have.
Richard

[ford38v8]

Originally Posted by Ricosan

Here is what I have.

The number on yours appears to have been obliterated, at least the picture doesn't show it. The only reason to obliterate that number would be if the turtle had been modified to accept a different gear than original to the turtle. Guys have done that because the turtle they need was not available. Remove the turtle and count the gear teeth, simple and quick. Then count the revolutions of the driveshaft to one revolution of an elevated wheel, which will indicate the differential ratio. (One elevated wheel will turn twice the ratio.) With that ratio and tire size, you can determine the correct turtle gear.

[Ricosan]

Good morning ford38V8, I don’t understand how I count the revolutions of the drive shaft inside of the torque tube. I can’t see it rotate. Do I need to remove the transmission cover from the floor?

Richard

[glennpm]

Hi Richard,

You may be able to count the driveshaft rotations by putting a crayon mark on the driveshaft gear through the window that's behind the turtle. You would need a helper for this, one rotating the rear wheel and the other counting the rotations through the turtle window. If you had a split clamshell it would be easier.

Pull the turtle first and count the teeth.

Glenn

[Ricosan]

OK, let me see if I have this straight. I will need to remove the transmission cover and then mark the gear on the torque tube that is exposed after removing the turtle. I count how many rotations this gear makes for one revolution of my rear tire.
I’ll count the number of teeth in the turtle.
I’m on it! I can’t do it today since I’m taking my wife for a ride this afternoon but Monday looks good.

Richard

[glennpm]

You may not have to take the transmission cover off although it will give you more light. The turtle cutout is on the side of the torque tube so you'll need to figure the best access to mark and count the axle rotations.

[V8COOPMAN]

Originally Posted by Ricosan

OK, let me see if I have this straight. I will need to remove the transmission cover and then mark the gear on the torque tube that is exposed after removing the turtle. I count how many rotations this gear makes for one revolution of my rear tire.
I’ll count the number of teeth in the turtle.
I’m on it! I can’t do it today since I’m taking my wife for a ride this afternoon but Monday looks good.

Richard

Richard.....The pictures below are of a 1935 & a 1940 Ford, but the idea is the SAME. Keep in mind that your '33 FLOOR opening (for access) will probably be somewhat different. These pics might help you pre-plan your mission.

Coop

[glennpm]

I don't think what I posted #40 will work since the end of the snap ring may not be visible after you turn the wheel two times. The other rear wheel must be on the ground.

Pick either the end of the snap ring or other point on the driveshaft gear that you can use as as an indicator. Line it up with the edge of the turtle opening then make a mark on the tire at the bottom perpendicular to the ground.

Rotate the jacked wheel two times. Now rotate the rear wheel slowly until the end of the snap ring or other indicator is even with the edge of the opening. The rear wheel is now rotated some fraction of a full rotation. Divide that total wheel rotation number by 2. The result is then divided into the rotations of the driveshaft giving you the gear ratio.

Example for a 4:11:

- 2 wheel rotations
- snap ring or other indicator is not visible
- rotate wheel again slowly until the driveshaft has rotated 5 times with the indicator even with the opening
- Wheel has been rotated 2.43 turns to accomplish this

Rear end ratio = 5/(2.43/2) = 4.11 (I cheated to make it work out :-)

Hope you get the idea.

[ford38v8]

Driveshaft rotation will match engine rotation when transmission is in direct drive. Position of the fan blade will indicate engine position.

[glennpm]

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So with 5 rotations of the driveshaft with snap ring end as indicated in post #44, the tire mark would be in these positions for the three most likely rear-end ratios.

4.11 ---> 2.43 rotations
3.78 ---> 2.65 rotations
3.54 ---> 2.82 rotations



Glenn

[Ricosan]

OK, I think I got it. I removed the transmission cover and the turtle. I had my brother slowly turn the right rear wheel for 2 revolutions and then slowly approached the .43 and it came up on the gear part I had selected to watch. It looks like 411 rear end.
I counted the number of teeth in the turtle - 24.
Glenn, I was unable to download your chart. Will that help determine which turtle tooth count would work with a 411 rear end.

Richard

[glennpm]

Great!
You'll need either a 20 or 21, most likely a 20. The turtle casing you have with a 24 won't work. I believe that for a casing you can only go with a two tooth difference.

Exactly what over or under speed were you at what MPH?

[Ricosan]

When my speedometer registers 35mph my actual speed is 45mph.

I should be looking for 20 or 21. I think I saw one at third gen.

Richard

[glennpm]

Excellent! A 20 tooth should be pretty close.

[Ricosan]

Found a nice looking used 21 tooth turtle in the swap area. The ad was from last year but just thought I would give a holler. He still had it! Hopefully it will come quickly. I’ll post the results.

Richard

[glennpm]

so how have you made out with this Richard?

Glenn

[Ricosan]

Got the 21 tooth turtle installed this morning. Took it out for a test. I am showing a registered speed on my speedometer of 35, actual speed is 41. I came down from 24 teeth to 21 teeth and I got about 4 mph improvement. Maybe a 19 or even an 18 tooth would put me on the money. Thoughts?

Richard

[Ricosan]

I just hit me. My ‘34 had a 411 rear end and 17 X 5.50 tires. Same as my ‘33. I went back through my photos and found a pic of the turtle. It’s a 21 tooth and the speedometer was always spot on.
So now the question is why am I reading 5 or 6 mph off with the same setup? Is it possible that I misread the rear end ratio?
I’m not sure if it’s significant but the needle is not as steady with this new turtle.

Richard

[glennpm]

Boy Richard, I expected that you would be closer to true speed than you are.
It could it be that someone replaced the gear in that "21" you have with a higher count gear? I'd pull the turtle again and count the teeth. I thought a 20 tooth gear would be correct but perhaps a 19? I know that Bratton's sells nylon gears for the turtle.

Glenn

[glennpm]

You may also have the wrong driving gear tooth count, part numbers 17285;
the one that mounts to the driveshaft but changing that would be a big job.

[V8COOPMAN]

Originally Posted by glennpm

You may also have the wrong driving gear tooth count, part numbers 17285;
the one that mounts to the driveshaft but changing that would be a big job.

I DID NOT realize that there were more DRIVE GEARS than one.

Coop

.

[glennpm]

Yes there are two

- The driving gear is the one that is mounted on the driveshaft

- The driven gear is the one in the turtle.

Until I looked into this today, I didn't realize there were several driving gear options.

[Ricosan]

Glenn, it looks like this setup should be working. Being it’s the exact mechanical ratio as my ‘34. - 411/21 teeth/17X5.50. If after tooth count I get 21 teeth, it would leave only the driving gear as suspect.

Richard

[glennpm]

I agree with you.

If it is the same as your 34 and the driving gear is the bad boy, rather than changing it, I would go further down on the driven or turtle gear teeth. The gears only, like from Bratton's for example, are about 15 to 20$ I believe.

[glennpm]

If you buy new gears, check on the minimum teeth number that will work with your 21 turtle cap which I believe is 19 teeth.

[tubman]

You would only get one "tooth movement" per revolution of the drive shaft, no matter what the pitch, wouldn't you. Thus, is seems that the different "drive" gears are necessary only tp provide the proper mesh with the different "driven" gears. I don't see how changing the "drive" gear could change the reading of the speedometer as lomg as the "driven" gear is not changed.

[Ricosan]

Good morning Guys,
Tubman, I think I see your point. I am proceeding with the assumption that the drive gear has not been changed. I think that I will eventually find the right driven gear to bring the speedometer into proper calibration.
Glenn, I checked Brattons but they had only one turtle gear and I believe it was 21 tooth. I’ll keep checking.

Richard

[glennpm]

Hi Tubman,

The driveshaft driving gear does matter. Each time there is engagement between one of the driving, driveshaft gear teeth, the turtle driven gear is rotated. More teeth faster rotation. Fewer teeth less.

Glenn

[tubman]

Originally Posted by glennpm

Hi Tubman,

The driveshaft driving gear does matter. Each time there is engagement between one of the driving, driveshaft gear teeth, the turtle driven gear is rotated. More teeth faster rotation. Fewer teeth less.

Glenn

I don't agree with this. How can one driveshaft revolution cause the driven gear to move anything other than one tooth, no matter what the pitch?

"More teeth faster rotation. Fewer teeth less.' applies to the driven gear only.

[glennpm]

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"More teeth faster rotation. Fewer teeth less.' applies to the driven gear only.

No, it applies to both. As the driving driveshaft gear rotates, one of the driving teeth engages, more partial rotation, the next tooth engages, etc. The turtle is fixed along the driveshaft longitudinal axis and the turtle doesn't track back and forth longitudinally.

Re., "I don't agree with this. How can one driveshaft revolution cause the driven gear to move anything other than one tooth, no matter what the pitch?"

Because the driving gear has more than one tooth per revolution.

[tubman]

Originally Posted by glennpm

"More teeth faster rotation. Fewer teeth less.' applies to the driven gear only.

No, it applies to both. As the driving driveshaft gear rotates, one of the driving teeth engages, more partial rotation, the next tooth engages, etc. The turtle is fixed along the driveshaft longitudinal axis and the turtle doesn't track back and forth longitudinally.

Re., "I don't agree with this. How can one driveshaft revolution cause the driven gear to move anything other than one tooth, no matter what the pitch?"

Because the driving gear has more than one tooth per revolution.

No matter how many teeth it has, it can only move any tooth 1 increment forward per revolution.

[glennpm]

The worm engages one driven tooth but loses contact until the next driving gear takes over and this happens 7 times per driveshaft rotation. Stock Ford cars have 7 teeth on the driving gear.

I'm done :-)

[Ricosan]

Hey Guys,

I was able to score a new 19 tooth turtle from 3rd gen and installed it on my car in place of the 21 tooth I installed last week. Took it for a drive this afternoon and it is registering accurate speeds at all points from slow to fast. Such a great feeling.
Thanks to all of you who contributed your time, knowledge and experience to helping to find working solutions. I’m learning so much!
Richard

[glennpm]

Great news!

Glenn