speedometer adjustment for a 31 roadster

[old31]

When checked against a GPS my speedometer reads 7-10 MPH faster than actual.

Other than my foot on the gas, is there any adjustment that I can do to fix it?

[roblesterjr04]

Have you replaced the sending gear recently? Or put on different wheels?

[MAG]

Speedometer drive gear must match the Ring&Pinion ratio and the tire size.
3:54 R&P, 21" tires =17 tooth gear.
3:54 R&P, 19" tires =18 tooth gear.
3:78 R&P, 19" or 21" tires = 19 tooth gear.
4:11 R&P, 19" or 21" tires = 21 tooth gear. (pretty sure but not postive).

[BILL WILLIAMSON]

Well, if it's TOO FAST, you won't be getting TICKETS!
Bill Slow

[Charlie Stephens]

How is your odometer working? If it is off the same amount you probably need a different gear that bolts to the front of the torque tube. Has it always been this way? Did you change anything recently?

Charlie Stephens

[Mark in MT]

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Check the odometer against the mile posts on the highway, if the gearing is off in the speedometer system then the odometer will be off. If the odometer is off in the same direction and the same percentage as the speedometer, then the cable needs to geared differently. If the odometer is off by a different amount or direction that the speedometer, then the speed portion of the speedometer head needs calibration. There is no calibration in the dash unit for the odometer, but the speedometer can be adjusted to make it right. I have a Stewart Warner bench "Speed Analyzer", basically a big speedometer that is accurate with an extra out put to plug your unit into to test it. Then the speedometer is tweeked to get it to run right. Contact me if you have other questions.

[duke36]

In addition to the prior comments and threads, another possible option is to purchase a USA made ratio adapter that attaches to the speedo drive gear at the torque tube. They are on ebay for about $90 and include small parts to fit the square or round tips on the speedo cable. Also they are available with many speed- up or speed -down ratios (20%, etc.). Some folks with overdrives and non stock trannies have used these.

[old31]

Originally Posted by roblesterjr04

Have you replaced the sending gear recently? Or put on different wheels?

I have not changed the sending unit. The tires are standard 19" Firestones.

[old31]

Originally Posted by MAG

Speedometer drive gear must match the Ring&Pinion ratio and the tire size.
3:54 R&P, 21" tires =17 tooth gear.
3:54 R&P, 19" tires =18 tooth gear.
3:78 R&P, 19" or 21" tires = 19 tooth gear.
4:11 R&P, 19" or 21" tires = 21 tooth gear. (pretty sure but not postive).

I just bought the car so I am a newbie with a bunch of questions, and my manual's are on there way.

How would I check the R&P and the tooth gear?

[old31]

Originally Posted by Charlie Stephens

How is your odometer working? If it is off the same amount you probably need a different gear that bolts to the front of the torque tube. Has it always been this way? Did you change anything recently?

Charlie Stephens

I am new to the car and have not changed anything. The odometer works fine but as Mark mentioned I suspect it is off as well by the same amount as the speedometer.

[Mike V. Florida]

Originally Posted by old31

I am new to the car and have not changed anything. The odometer works fine but as Mark mentioned I suspect it is off as well by the same amount as the speedometer.

As has been stated;

Odometer correct, speed off; an adjustment may work. Speedo info
Odometer incorrect, speed incorrect; gearing is off.

[Rowdy]

Should not be needed. If you know which gear ratio you have make sure the speedometer drive gear matches the gears you have. If that is correct then it is likely time to get a your speedometer rebuilt. Rod

[Dollar Bill]

How To Check Ring & Pinion

Remove all four spark plugs.
Jack up one rear wheel and mark the 12 o'clock position on the tire.
Hand crank engine 2 complete turns.
See where chalk mark on tire ends up:

Between 11 and 12 o'clock, ratio is 4.11
Between 12 and 1 o'clock, ratio is 3.78
Between 1 and 2 o'clock, ratio is 4.54

In some cases the ring and pinion tooth count can be found stamped on the banjo housing web or flange.

[old31]

Dollar, per your instructions I checked an unfortunately I have a 4.11. I would prefer to have a 3.54 or 78. No wonder I have to shift so quick.

I removed the speedometer gear and I have a 9-34-19. I counted the teeth and I have 19.

According to an article by Ed Eaton, and if I am reading his chart correctly I should have a 37-9 with 21 teeth.

Does anyone agree or disagree with the numbers?

I am guessing this is why my speedometer is 7-10MPH off.

[Rowdy]

21 teeth would be correct. Rod

[heneste]

If you are running an overdrive or plan on installing one, I've been told that the 4.11 gear ratio is recommended for use with the overdrives.

If you're not going to run with an overdrive, you can have the gear ring set changed in the rear and make sure the speedometer gear drive matches with whichever gear set you choose to install.

[Y-Blockhead]

Originally Posted by Dollar Bill

How To Check Ring & Pinion

Remove all four spark plugs.
Jack up one rear wheel and mark the 12 o'clock position on the tire.
Hand crank engine 2 complete turns.
See where chalk mark on tire ends up:

Between 11 and 12 o'clock, ratio is 4.11
Between 12 and 1 o'clock, ratio is 3.78
Between 1 and 2 o'clock, ratio is 4.54

In some cases the ring and pinion tooth count can be found stamped on the banjo housing web or flange.

Good info, can I assume you meant 3.54

[pooch]

Dunno if this the right way to adjust a speedo, but I bought 2 "restored and calibrated " kilometre ones from USA that are about 25 KPH out at 100 KPH, yes, that far out.

I moved some sort of sliding ring under the speedo head drum either way to the extremities of the slots and it changed the shown speed about 10 KPH either way.

No good for my wasted money on these 2 speedos still being out by heaps , but maybe possible to get your 6 MPH...

[J Franklin]

Pooch, did you give it a light oil? I think it has to do with lessened magnetism.

[updraught]

Maybe some oil from the South Pole ...

PS. I have one of those kilo speedos too. Got me worried now. Haven't tried it.

[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]

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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]

Originally Posted by Tom Wesenberg

... 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...r/man14-4.html

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

http://www.cabriolet.modelahouse.com...er/fischer.pdf

http://www.cabriolet.modelahouse.com...ter/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]

Originally Posted by 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.

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.

[stafford]

many thanks Dollar Bill

[papanick]

if you know how far it is off you can have the speedometer reset to mach your GPS reading.