speedometer adjustment for a 31 roadster

[old31]

So, how does teeth relate to speed registered?

Does 1 or 2 teeth more (or less) make the speedometer read faster or slower?

 

[Tom Wesenberg]

One tooth more will make the speedometer read slower, but the first thing to make accurate is the odometer.

 

[old31]

Thanks.

 

[old31]

Follow up:

I changed from a 19 tooth to a 21 tooth. This made 0-40MPH within 1-2 mph from the GPS. At 40 and above the speedometer is 15 mph off. So, when the speedometer says 60, I am really doing 45MPH. Also, when it reaches 40 on the speedometer the gauge will quickly advanced to 80 and then settle down.

I also checked it against the highway mile markers. The speedometer is 1/10 off per mile. So, when the 1 mile marker comes up, I am showing .9.

 

[Mike V. Florida]

It sounds like a good cleaning and lubrication is in order.

 

[Tom Wesenberg]

I agree with Mike. Go back to the 19 tooth so the miles is accurate, then lube the head, or send it out for service.

 

[CarlG]

... send it out for service.

On this, I submit to the expert craftsmen. Leonard Nichols (Pappanick) does an excellent job, fast and reasonable price.

 

[Mark in MT]

Sounds like the speedcup may be rubbing on the magnet, causing a drag which will make it run erratically, and too fast. Either way, it needs to come apart to be looked at and calibrated. I have a F.W. Stewart "Speed Analyzer" on the bench that I use to diagnose and calibrate the instruments. Basically it is a variable speed motor with 2 out puts, 1 to a 9 inch diameter speedometer head which is your standard, and the other which you hook up to the speedo to be tested. This is a great way to see and be able to adjust the unit without putting it back in the car. Usually takes about an hour to service and calibrate a speedo to +-2mph from 20 to 60 mph.

 

[old31]

I will put the 19 tooth back in and lube the head clean and oil it.

When you say lube the head, are you talking about the gears shown in the link below?

http://www.cabriolet.modelahouse.com/tech/speedometer/man14-4.html

I have this doc for the speedometer. Is there anything else that might be more helpful?

http://www.cabriolet.modelahouse.com/tech/speedometer/fischer.pdf

http://www.cabriolet.modelahouse.com/tech/speedometer/index.html

 

[Tom Wesenberg]

I put a drop of motor oil and a dab of light grease on each of the gears and pivots, and my speedometer works fine, plus the odometer is also accurate to 1%. But if you find the wheel rubbing, as Mark mentioned, then I'd send it out for repair.

 

[old31]

I put a drop of motor oil and a dab of light grease on each of the gears and pivots, and my speedometer works fine, plus the odometer is also accurate to 1%. But if you find the wheel rubbing, as Mark mentioned, then I'd send it out for repair.

OK, I will do the same. Per your last suggestion I did reinstall the original 19 steel tooth gear that I had. The steel gear with about 1,500 miles on it looks new.

What do you think of the pictures of this nylon tooth gear? It is brand new and has a total of about 65 miles. I was surprised to see how the tops of the teeth are all cupped. What would cause this?

 

[Tom Wesenberg]

I don't know, as I've only used original gears and never had a problem.

 

[Mark in MT]

Ford used different gear housings for the different tooth count gears as the diameters are different. The actual pot metal housing is the same, but the curved surface where it meets the torque tube is machined closer to the shaft center line on the smaller gears, this keeps the 2 gears in the proper mesh. If you put a small gear in a housing designed for a larger one, the driven gear will engage only on the tips of the teeth, causing wear like shown.

 

[old31]

Interesting.

They just don't tell you this stuff when you go looking to buy a new and different gear.

 

[Mark in MT]

I have heard of someone using a drum sander to bring the curved mounting surface closer to the shaft centerline. If I recall correctly, the torque tube is 3" diameter.

 

[old31]

Follow up:

I cleaned the speedo cable and coated it with Kable ease.

I took the speedometer apart again. Greased and oiled all contacts. The speedcup was rubbing against the magnet, I could see the scratches. The speedcup was adjusted and now from 0-60 it runs very smooth with no jitters.

With the original steel 19 tooth gear the mile markers are right on 100%, mile per mile.

Its better and close enough. From 0-35MPH I am reading about 4MPH off. So, 32MPH on the speedometer is 35 on the GPS. From 35-55 MPH both the speedo and GPS are identical.

Also, what do the stamped numbers on the speedometer mean?

 

[Mark in MT]

I am guessing here, but I believe that those are numbers of the mold or die that made the part. The numbers give some tracibility back to the source in case of bad parts, say that during inspection that they had 3 bads with a 12 on them, they need to look at die 12.

 

[Floats]

Hi Gents,
My rebuilt Km speedo also came from a forum member from the US. The speedo ran fine for a while, until I had to do an engine overhaul which took just under a year. I got my car running again last week. The speedo and distance meter runs fine, up to 40Kph. The speed then stays pegged at 40(GPS reads up to 60km) the distance indicator keeps adding the kilos normally. This speedo has only done about 500 kilos since installation.
Any suggestions would be much appreciated.

 

[stafford]

which gear do you use to check the ring and pinion ratio 1st 2nd or 3rd, when turning the crank handle with one rear wheel raised

 

[Dollar Bill]

Direct drive or third gear.