Speedometer drive gears
 

I didn't want to hijack SSssteamer's thread on the same subject so I started this one.
Firstly, some background. My 1930 CCPU is fitted with a 26% Mitchell O/D and 3.78 diff but the speedo reads about 16-17% fast. Clearly, the speedo drive gear should be about that % larger. The O/D, I believe comes fitted with an 18 tooth gear but for some reason known only to the previous owner, it has a 17 tooth gear in it. By my calculations, I need a 20 tooth gear (black). I plan in fitting a 3.54 diff to it soon and for that, I'd need a 19 tooth gear (pink).
The cost of freight from the US is stupid, as has been discussed here recently so I am hoping that armed with the right information, I might be able to buy them here. I am lead to believe that Mitchell uses gears etc from a more modern Ford gearbox in their O/Ds. If so, which one and even better, does anybody have a part number please?

Re: Speedometer drive gears
 

Does the odometer read out correctly?

Re: Speedometer drive gears
 

I haven't bothered to check that. It's the accuracy of the speedo that will save me a few tickets! I understand why you asked that - changing the gear will affect the odometer too.
Is there an adjustment inside the speedo that might fix this and not affect the odometer?

Re: Speedometer drive gears
 

Check the accuracy of the odometer, that will tell you if you have the correct drive gear as the odometer is a direct drive from the drive gear.

The speed cup moves based on a magnetic field that can be adjusted in the Stewart Warner speedometer.

So if the odometer is correct, you have a calibration problem.

If the odometer if off then install the correct drive gear for your differential, then if the speed cup is off you can calibrate the speedometer to correct the indicated speed.

Here is a link to Gordon Fishers instructions to rebuild and calibrate a speedometer, it is for the SW oval speedometer, but will help get you through the round speedometer.

http://www.modelahouse.com/tech/spee...r/fischer.html

Re: Speedometer drive gears
 

Thanks 160B, We are going on a drive in the P/U soon so I will compare the distance covered against the GPS on part of it. I had considered whether speedo AND odometer were out but wasn't too concerned about the odo. Best to have both right, though

Re: Speedometer drive gears
 

Here is a photo of a Stewart Warner oval speedometer showing the slip plate that affects the magnetic field to adjust the speed cup to correct the indicated speed. The round speedometer has the same slip plate.

Left speedometer in photo below - Slip plate covers the air gap, reduces the magnetic field slows down the speed cup. Decreases indicated speed.

Right speedometer in photo below - Slip plate uncovers the air gap, increases the magnetic field speeds up the speed cup. Increases indicated speed.

Re: Speedometer drive gears
 

I was told that the transmissions involved are:

Ford T5
Tremec TKO
Tremec T5
Tremec Magnum

Unverified info:

I was given these Ford p/n:

Note have not tried to install these gears in Mitchell OD yet

C1DZ-17271-A black gear is inside BUT bag is opened when bought from dealer.

CODZ-17271-B same as above opened bag with pink gear

Steve Becker at Bert's says that Sue Mitchell can give you the P/Ns on the phone.

http://mitchelloverdrivemfg.com/

Note have not tried to install in Mitchell OD

Posted recently by Tom Endy:


Speedo housing gears (according to Snyder)
17 teeth – for early 1928 - 21” wheels and 10-37 (370) ring & pinion
18 teeth – for 1928-1929 - 21” wheels and 9-34 (378) ring & pinion
19 teeth – for 1930-1931 - 19” wheels and 9-34 (378) ring & pinion
20 teeth – for 1928-1929 - 21” wheels and 9-37 (411) ring & pinion
21 teeth – for 1930-1931 - 19” wheels and 9-37 (411) ring & pinion
Ring & pinion ratios
Original Ford production:
370 – 10-37
378 – 9-34
411 – 9-37
After market:
354 – 11-39 (Speedo gears for these two R&P ratios would have to have a tooth count lower than 17)
327 – 11-36
Mitchell overdrive speedo gears
(According to Mitchell)
Available from Ford Dealers
16 teeth – wine (maroon)
17 teeth – white
18 teeth – yellow – for 378, both 19’ & 21” tires (Normally delivered with 26% overdrive)
19 teeth – pink
20 teeth – black – for 378 with 16” wheels (determined by Bryan Thompson)
21 teeth – red
Each gear color changes speed by 2.5 miles
Ford part numbers – nominal price $14.97 (2017)
16 teeth – AWR-SPUN-10016
17 teeth – AWR-SPUN-10017
18 teeth – AWR-SPUN-10018
19 teeth – AWR-SPUN-10019
20 teeth – AWR-SPUN-10020
21 teeth – AWR-SPUN-10021


Part numbers are unknown to local Denver Ford Dealer...

NOTE: AWR-SPUN numbers are listed on Summit Racing website
FWIW ...

Re: Speedometer drive gears
 

Thanks all. We have just decided to go on a run with one of our clubs next Wednesday. I'll check the accuracy of the odometer against the GPS then and decide what to do, adjust the air gap or change the gear.
160B, They are very detailed instructions, Thank you.
I guess adjusting the air gap correctly is trial and error, right?

Re: Speedometer drive gears
 

Found this on an Ebay posting selling gears:

SPEEDOMETER GEAR YELLOW 18 TOOTH BRAND NEW OEM ALL FORD 1990-1998 #CODD-17271-B

THis will get Ford dealer parts guys on the right track ...

Re: Speedometer drive gears
 

I've used a Speedo Gear Ratio adapter (some on ebay) available in different ratios which are easy to calculate based on over or under speedo readings. The final in car reading has been exact when compared to road speed sensing equip. It installs between the cable end and speedo cable connection on the tranny or existing gear.

Re: Speedometer drive gears
 

FWIW

If your speedometer is not indicating an accurate MPH, first check to see if the odometer is indicating accurate miles.

If the odometer is accurate than the problem is in the speedometer calibration.

If the odometer is not correct then the drive gear at the driveline or overdrive is incorrect.

Change the drive gear and then check the indicated odometer and indicated MPH, if both are correct problem solved.

If the odometer is not correct, wrong gear, change to correct gear, when you get the correct gear and the odometer is correct and the indicated MPH is not correct than you also have a calibration problem.

The odometer is a direct drive and there are no adjustments other than installing the correct gear.

The indicated MPH can be adjusted in the calibration process.

I hope this helps

Re: Speedometer drive gears
 

160B,
We will be out in the car on Wednesday and will check the odometer. I had already decided to try to get both speedometer and odometer correct by doing as you have suggested. The info you posted on Speedo overhaul and adjusting the air gap will be very helpful. I imagine that 16-17% error is at the extreme end of errors so I will probably have to change the air gap quite a bit. Fine tuning might be trial and error though. Thanks for your help.

Re: Speedometer drive gears
 

Synchro909,

You are on the right track. The 16 - 17 % error indicates to me it may be a combination of the drive gear and air gap. Air gap usually is a 5 to 7 mph maybe a little more adjustment. And like you said it is a trial and error process.

Let us know how it works out. I will watch for your results and provide any appropriate advice.

I am sure you are dealing with an oval speedometer as the depression resulted in very few late 30 or 31 Model A Fords being imported into Australia.

My wife have been to several meets in AU, Shannons 2001 Canberra, and the Model A meets in Toowoomba 2002, Adelaide 2006 and Launceston 2010, and have always enjoyed the meets and the friendships.

good on ya mate!!

Re: Speedometer drive gears
 

It's actually a 1930 CCPU I bought in Arizona a while back. It has a round speedo but you are correct - few 1930 or '31 cars here, in fact I'm told none were brought here in 1931 because there were so many unsold '30 models. They could still be bought new in about 1933. The depression hit here harder than over there!
Glad you enjoyed your rallies here. Are you coming to the next national about September 2018? It's at Murray Bridge, about 75 km (45 miles) towards Melbourne from Adelaide.

Re: Speedometer drive gears
 

When you get your speedometer apart for calibration it is a good time to oil the unit. Remove the two brass cups in the below photo and remove the wicks and clean them in a good solvent, dry them, reinstall the wicks, oil the wicks and replace the two brass cups.

Re: Speedometer drive gears
 

Thanks 160B,

Good speedometer info!

I will make checks and adjust gap if needed after getting correct gear in Mitchell ...

It has 3.78s with yellow gear and 6.00-16 Bias ply and will put on Coker Radial 6.00 16's then start checks ... so I suspect that it is off at least 2.5 MPH.

Re: Speedometer drive gears
 

Re: Speedometer drive gears
 

Well, today I was out in the car and tested the odometer against the GPS. Over 15 miles, the odo was out by only 0.2 miles so it seems the whole 16-17% error is in the speedo head and that changing the driven gear size on the cable might help the speedo but make the odo way out. I'm told that there is not that much adjustment in the head so what do I do?:confused:
All advice and info appreciated.

Re: Speedometer drive gears
 

Anyone???

Re: Speedometer drive gears
 

Better buy another, Round or Oval, Or like me use GPS, Stops getting speeding tickets in built areas in strange towns ,