The Ford Barn

old31 · 03-11-2016, 04:17 PM

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 · 03-11-2016, 04:31 PM

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

MAG · 03-11-2016, 07:12 PM

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 · 03-11-2016, 09:24 PM

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

Charlie Stephens · 03-11-2016, 09:33 PM

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 · 03-11-2016, 09:34 PM

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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 · 03-12-2016, 12:00 PM

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 · 03-12-2016, 06:41 PM

Quote:

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 · 03-12-2016, 06:44 PM

Quote:

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 · 03-12-2016, 06:47 PM

Quote:

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 · 03-12-2016, 11:26 PM

Quote:

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 · 03-13-2016, 12:14 AM

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 · 03-13-2016, 06:15 AM

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 · 03-16-2016, 10:59 AM

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 · 03-16-2016, 11:24 AM

21 teeth would be correct. Rod

heneste · 03-16-2016, 11:33 AM

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 · 03-16-2016, 11:35 AM

Quote:

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 · 03-16-2016, 01:45 PM

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 · 03-16-2016, 04:03 PM

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

updraught · 03-16-2016, 05:57 PM

Maybe some oil from the South Pole ...

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

03-11-2016, 04:17 PM	#1
old31 Senior Member Join Date: Jan 2016 Posts: 2,103	speedometer adjustment for a 31 roadster 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?

03-11-2016, 04:31 PM	#2
roblesterjr04 Senior Member Join Date: Mar 2015 Location: Hanover, PA Posts: 130	Re: speedometer adjustment for a 31 roadster Have you replaced the sending gear recently? Or put on different wheels? __________________ -Rob 1929 Fordor Leatherback

03-11-2016, 07:12 PM	#3
MAG Senior Member Join Date: May 2010 Location: Austin, Texas Posts: 925	Re: speedometer adjustment for a 31 roadster 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 noticed the harder I work the luckier I get!

03-11-2016, 09:24 PM	#4
BILL WILLIAMSON Senior Member Join Date: Dec 2010 Location: FRESNO, CA Posts: 12,560	Re: speedometer adjustment for a 31 roadster Well, if it's TOO FAST, you won't be getting TICKETS! Bill Slow __________________ "THE ASSISTANT GURU OF STUFF"

03-11-2016, 09:33 PM	#5
Charlie Stephens Senior Member Join Date: May 2010 Location: Southern California Posts: 7,033	Re: speedometer adjustment for a 31 roadster 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

03-11-2016, 09:34 PM	#6
Mark in MT Senior Member Join Date: May 2010 Location: Western MT Posts: 218	Re: speedometer adjustment for a 31 roadster Sponsored Links (Register now to hide all advertisements) 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. __________________ Mark in MT Always looking for another opportunity to be wrong.

03-12-2016, 12:00 PM	#7
duke36 Senior Member Join Date: Jun 2015 Posts: 1,414	Re: speedometer adjustment for a 31 roadster 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.

03-13-2016, 12:14 AM	#12
Rowdy BANNED Join Date: May 2010 Location: Gothenburg Nebraska Just off I-80 Posts: 4,893	Re: speedometer adjustment for a 31 roadster 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 __________________ Do the RIGHT thing - Support the H.A.M.B. Alliance!!!!

03-13-2016, 06:15 AM	#13
Dollar Bill Senior Member Join Date: Oct 2014 Location: Keystone Heights, FL Posts: 647	Re: speedometer adjustment for a 31 roadster 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. __________________ I Love Anything That Turns Money Into Noise

03-16-2016, 10:59 AM	#14
old31 Senior Member Join Date: Jan 2016 Posts: 2,103	Re: speedometer adjustment for a 31 roadster 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.

03-16-2016, 11:24 AM	#15
Rowdy BANNED Join Date: May 2010 Location: Gothenburg Nebraska Just off I-80 Posts: 4,893	Re: speedometer adjustment for a 31 roadster 21 teeth would be correct. Rod __________________ Do the RIGHT thing - Support the H.A.M.B. Alliance!!!!

03-16-2016, 11:33 AM	#16
heneste Senior Member Join Date: Nov 2010 Location: Ottawa,Ontario, Canada Posts: 271	Re: speedometer adjustment for a 31 roadster 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.

03-16-2016, 01:45 PM	#18
pooch Senior Member Join Date: Sep 2010 Location: South Coast NSW Australia Posts: 2,596	Re: speedometer adjustment for a 31 roadster 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...

03-16-2016, 04:03 PM	#19
J Franklin Senior Member Join Date: May 2010 Location: Oregon Posts: 5,963	Re: speedometer adjustment for a 31 roadster Pooch, did you give it a light oil? I think it has to do with lessened magnetism.

03-16-2016, 05:57 PM	#20
updraught Senior Member Join Date: Feb 2015 Location: Australia Posts: 1,971	Re: speedometer adjustment for a 31 roadster Maybe some oil from the South Pole ... PS. I have one of those kilo speedos too. Got me worried now. Haven't tried it. Last edited by updraught; 03-16-2016 at 06:13 PM.