Go Back   The Ford Barn > General Discussion > Model A (1928-31)

Sponsored Links (Register now to hide all advertisements)

Reply
 
Thread Tools Display Modes
Old 05-28-2017, 04:58 PM   #1
JOHN CT
Senior Member
 
JOHN CT's Avatar
 
Join Date: May 2010
Location: In my garage
Posts: 465
Default Speedo gear

My speedometer is off by 5 mph when I reach 35 + mph. Slower speeds its still not accurate. It's a stock 31 with 19 in tires. Where do I begin to see if I have the right gear? By looking in the catalogs I need to know what gear ratio I have. Isn't there a way by jacking up the rear and turning the wheel to find the gear ratio? Can you explain how it is done.
Thanks
__________________
31 Tudor
66 Bonneville
57 Chevy pickup 27 T roadster pick up
JOHN CT is offline   Reply With Quote
Old 05-28-2017, 05:02 PM   #2
SeaSlugs
Senior Member
 
SeaSlugs's Avatar
 
Join Date: May 2010
Location: Central, IL
Posts: 3,968
Default Re: Speedo gear

hmm its going to be a bit tricky but put the car in 3rd, jack up one wheel, and mark the tire - then count how many times you need to hand crank the engine to get the tire to rotate one revolution. like a ratio of 3.54. Its really 3.54:1 meaning it takes 3.54 turns of the input(driveshaft) to get the output (wheel) to turn one revolution.
__________________
1929 Model AA - Need long splash aprons!
SeaSlugs is offline   Reply With Quote
Sponsored Links (Register now to hide all advertisements)
Old 05-28-2017, 05:17 PM   #3
Charlie Stephens
Senior Member
 
Join Date: May 2010
Location: Southern California
Posts: 7,017
Default Re: Speedo gear

Quote:
Originally Posted by JOHN CT View Post
My speedometer is off by 5 mph when I reach 35 + mph. Slower speeds its still not accurate. It's a stock 31 with 19 in tires. Where do I begin to see if I have the right gear? By looking in the catalogs I need to know what gear ratio I have. Isn't there a way by jacking up the rear and turning the wheel to find the gear ratio? Can you explain how it is done.
Thanks
How is your odometer? If it is correct then you need to fix your speedometer and not mess around with the gear on the torque tube.

Charlie Stephens
Charlie Stephens is offline   Reply With Quote
Old 05-28-2017, 06:05 PM   #4
JOHN CT
Senior Member
 
JOHN CT's Avatar
 
Join Date: May 2010
Location: In my garage
Posts: 465
Default Re: Speedo gear

Quote:
Originally Posted by Charlie Stephens View Post
How is your odometer? If it is correct then you need to fix your speedometer and not mess around with the gear on the torque tube.

Charlie Stephens
Okay how do I check my speedometer for accuracy ?
__________________
31 Tudor
66 Bonneville
57 Chevy pickup 27 T roadster pick up
JOHN CT is offline   Reply With Quote
Old 05-28-2017, 06:14 PM   #5
1955cj5
Senior Member
 
1955cj5's Avatar
 
Join Date: Apr 2015
Location: Boise, Idaho
Posts: 1,576
Default Re: Speedo gear

I had tried some of those roll the car or lift one wheel and crank the engine by hand..

I finally jacked up the rear end, removed the fill plug, cleaned one of the ring gear teeth with a swab and marked it...then turned the rear end one tooth at a time and counted the teeth....I'm not sure if you could see the mark if the rear end were full

34 teeth you probably have a 3:78 to 1

other ratios here.

http://www.fordgarage.com/pages/rearaxleratios.htm

I used a hand held GPS to check speedo accuracy.....I realize you may not have one....
__________________
Early '29 CCPU that had a 4-speed, but not any more.......in the family since '62
1955cj5 is offline   Reply With Quote
Old 05-28-2017, 06:22 PM   #6
JOHN CT
Senior Member
 
JOHN CT's Avatar
 
Join Date: May 2010
Location: In my garage
Posts: 465
Default Re: Speedo gear

Sponsored Links (Register now to hide all advertisements)
Quote:
Originally Posted by 1955cj5 View Post
I had tried some of those roll the car or lift one wheel and crank the engine by hand..

I finally jacked up the rear end, removed the fill plug, cleaned one of the ring gear teeth with a swab and marked it...then turned the rear end one tooth at a time and counted the teeth....I'm not sure if you could see the mark if the rear end were full

34 teeth you probably have a 3:78 to 1

other ratios here.

http://www.fordgarage.com/pages/rearaxleratios.htm

I used a hand held GPS to check speedo accuracy.....I realize you may not have one....
I use a gps that's how l know that is not accurate.

Thanks for the chart that shows me the different gear ratios. That will be the best way to see witch ratio I have.

Then I can check witch speedo gear I have.
__________________
31 Tudor
66 Bonneville
57 Chevy pickup 27 T roadster pick up
JOHN CT is offline   Reply With Quote
Old 05-28-2017, 06:29 PM   #7
1955cj5
Senior Member
 
1955cj5's Avatar
 
Join Date: Apr 2015
Location: Boise, Idaho
Posts: 1,576
Default Re: Speedo gear

The Judging Standards have a chart showing the different speedo gear turtles..Section 4 page 15...revised 2011

I needed a 19 tooth turtle gear for my 3:78 ..I have 21" wheels but the outside diameter may be the same as 19's

Also there is this..
Attached Files
File Type: pdf ring & pinion MAFCA.pdf (78.8 KB, 24 views)
__________________
Early '29 CCPU that had a 4-speed, but not any more.......in the family since '62
1955cj5 is offline   Reply With Quote
Old 05-28-2017, 06:45 PM   #8
kd4lok
Member
 
kd4lok's Avatar
 
Join Date: Sep 2013
Location: Central FL
Posts: 72
Default Re: Speedo gear

Quote:
Originally Posted by SeaSlugs View Post
hmm its going to be a bit tricky but put the car in 3rd, jack up one wheel, and mark the tire - then count how many times you need to hand crank the engine to get the tire to rotate one revolution. like a ratio of 3.54. Its really 3.54:1 meaning it takes 3.54 turns of the input(driveshaft) to get the output (wheel) to turn one revolution.
I did not understand initially, but a recent thread advised to count TWO turns of the tire when one wheel is jacked up. I used this method to confirm that 3.78 is my ratio.
__________________
Bob
kd4lok is offline   Reply With Quote
Old 05-28-2017, 06:59 PM   #9
1955cj5
Senior Member
 
1955cj5's Avatar
 
Join Date: Apr 2015
Location: Boise, Idaho
Posts: 1,576
Default Re: Speedo gear

Quote:
Originally Posted by kd4lok View Post
I did not understand initially, but a recent thread advised to count TWO turns of the tire when one wheel is jacked up. I used this method to confirm that 3.78 is my ratio.
Look at post #22.....and then read some of the others as there were some additional things to do..

https://www.fordbarn.com/forum/showt...=177353&page=2
__________________
Early '29 CCPU that had a 4-speed, but not any more.......in the family since '62
1955cj5 is offline   Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Sponsored Links (Register now to hide all advertisements)


All times are GMT -5. The time now is 06:46 PM.