|
Sponsored Links (Register now to hide all advertisements) |
|
|
Thread Tools | Display Modes |
08-28-2015, 11:24 PM | #1 |
Senior Member
Join Date: Apr 2015
Location: Albuquerque, NM
Posts: 441
|
Unknown Differential Ratio
My '30 Town Sedan seems quite a bit original, but not 100%. So, I really bought a pig-in-a-poke. From all I've learned on the Barn, and from my local club, I probably have a stock engine (though restamped...I can still read original # too, but title bears rest amp #).
My question is, I also haven't a clue as to the differential ratio. Stock is 3.78 to 1, I believe, and my speedometer reads about 7 or 10 mph UNDER what I am doing, based on traffic flow. I'm thinking the speedometer needs to be restored, and is under-reading my speed. At 55mph based on traffic, it reads 42, so it seems like a progressive mis-read. So my other thought is a mismatched rear end and speedometer. Ideas? Chuck
__________________
... prosperity is not the product of charity but of industry - HENRY FORD |
08-28-2015, 11:29 PM | #2 |
Senior Member
Join Date: May 2010
Location: 60046
Posts: 888
|
Re: Unknown Differential Ratio
look at the speedo drive on the axleit will have numbers cast into it
you may have the wrong one (9-34) ect tk
__________________
anyone need some Model A restoration work done in Illinois? shoot me an email for pics and information [email protected] |
Sponsored Links (Register now to hide all advertisements) |
|
08-28-2015, 11:38 PM | #3 |
Senior Member
Join Date: May 2010
Location: Southern California
Posts: 7,032
|
Re: Unknown Differential Ratio
Check your odometer. Maybe with the mile markers on a country road. If your odometer is correct them you have a speedometer problem. The Auto Club of Southern California used to check speedometers with a unit that they moved from office to office on a regular schedule. I wonder if your local auto club (or maybe police department) does the same thing? Are you friendly with any police officers that could shoot your car with their radar gun?
Charlie Stephens |
08-28-2015, 11:39 PM | #4 |
Senior Member
Join Date: Apr 2015
Location: Albuquerque, NM
Posts: 441
|
Re: Unknown Differential Ratio
I will check it out in the morning. Thanx. That can tell me about the speedo.
Is there any kind of test to try up on the jacks, like a full turn of the engine , compared with how many turns of the rear wheels, say, in first gear? Will that give me the REAR END RATIO?
__________________
... prosperity is not the product of charity but of industry - HENRY FORD |
08-28-2015, 11:51 PM | #5 |
Senior Member
Join Date: Apr 2015
Location: Albuquerque, NM
Posts: 441
|
Re: Unknown Differential Ratio
Thanx Charlie. I can drive by one of those unmanned speed signs, for one.
I will take her out on a mile-marked road too, like you suggested.
__________________
... prosperity is not the product of charity but of industry - HENRY FORD |
08-29-2015, 01:32 AM | #6 | |
Senior Member
|
Re: Unknown Differential Ratio
Sponsored Links (Register now to hide all advertisements)
Quote:
__________________
What's right about America is that although we have a mess of problems, we have great capacity - intellect and resources - to do some thing about them. - Henry Ford II Last edited by Mike V. Florida; 08-30-2015 at 01:24 AM. |
|
08-29-2015, 01:40 AM | #7 |
Senior Member
Join Date: Apr 2015
Location: Albuquerque, NM
Posts: 441
|
Re: Unknown Differential Ratio
Thanx Mike. FANTASTIC! That's the kinda info I was digging for on the rear end! Chuck
__________________
... prosperity is not the product of charity but of industry - HENRY FORD |
08-29-2015, 01:41 AM | #8 |
Senior Member
Join Date: Apr 2015
Location: Albuquerque, NM
Posts: 441
|
Re: Unknown Differential Ratio
And Thanks, QGolden, wherever you are!
__________________
... prosperity is not the product of charity but of industry - HENRY FORD |
08-29-2015, 06:13 AM | #9 |
Senior Member
Join Date: Jul 2012
Location: Venice, FL
Posts: 648
|
Re: Unknown Differential Ratio
Charge your GPS at home and take it for a ride. On a straight run it will tell you exactly how accurate your speedo is.
My car had the wrong speedo gear in it. Al Leach |
08-29-2015, 06:28 AM | #10 |
Senior Member
Join Date: Jul 2014
Location: FRANKSTON TX
Posts: 117
|
Re: Unknown Differential Ratio
Lady"s Man: Down load speedometer app on iPhone if you have one.
Thanks Dana |
08-29-2015, 07:09 AM | #11 |
Senior Member
Join Date: May 2010
Location: Brookfield, NH
Posts: 102
|
Re: Unknown Differential Ratio
I have one of the free Speedo apps and it works great. It has a trip computer with info like top speed, average speed, stopped time, odometer, etc.
Pete |
08-29-2015, 11:37 AM | #12 |
Senior Member
Join Date: Apr 2015
Location: Albuquerque, NM
Posts: 441
|
Re: Unknown Differential Ratio
Ok, Wifey just read my speed with a phone speedo app. My speedo is way off, at 57, it read 45 or so. I will look for the number on the speedo cable, and also jack up car and do the rear end ratio check like Mike V Fl suggested.
Little by little, I'm finding the "unoriginal" surprises on this A.
__________________
... prosperity is not the product of charity but of industry - HENRY FORD |
08-29-2015, 12:29 PM | #13 | |
Senior Member
Join Date: Apr 2015
Location: Boise, Idaho
Posts: 1,578
|
Re: Unknown Differential Ratio
I copied this from above
Quote:
Is it accurate? I must be doing something wrong.. Marked the tire at 6 O'clock Transmission in third gear. Two revolutions with the hand crank Mark on the tire is at 5 O'clock after two revolutions of the engine and one plus revolutions of the tire...... I did this three times...same result each time... ???
__________________
Early '29 CCPU that had a 4-speed, but not any more.......in the family since '62 Last edited by 1955cj5; 08-29-2015 at 01:21 PM. |
|
08-29-2015, 01:12 PM | #14 |
Senior Member
Join Date: Apr 2015
Location: Boise, Idaho
Posts: 1,578
|
Re: Unknown Differential Ratio
So I found this on another site...
1) Jack up one rear wheel and chalk-mark the 12 o'clock position on the tire. (Make sure the slack is out of the drive train) 2) Hand crank engine 2 complete turns. 3) See where chalk mark on tire ends up. A) Between 11 and 12 o'clock, ratio is 4.11 B) Between 12 and 1 o'clock, ratio is 3.78 C) Between 1 and 2 o'clock, ratio is 3.54 This makes sense... Notice the mark is made at 12 O'clock instead of 6 O'clock In that case my mark would have ended up at 11 O'clock after two revolutions of the engine.. That would give me a 4:11 ratio which makes sense for a ccpu... EDIT...typo on the ratios...it's correct now...
__________________
Early '29 CCPU that had a 4-speed, but not any more.......in the family since '62 Last edited by 1955cj5; 09-14-2015 at 09:33 AM. |
08-29-2015, 02:59 PM | #15 | |
Senior Member
Join Date: Apr 2015
Location: Albuquerque, NM
Posts: 441
|
Re: Unknown Differential Ratio
Quote:
__________________
... prosperity is not the product of charity but of industry - HENRY FORD |
|
08-29-2015, 05:07 PM | #16 |
Senior Member
Join Date: May 2010
Location: At my kitchen table in Santa Rosa, Ca
Posts: 2,903
|
Re: Unknown Differential Ratio
that's what I use, speed box
__________________
If it would have been a snake it would have bit ya! i can't spell my way out of a paper bag! |
08-30-2015, 01:25 AM | #17 |
Senior Member
|
Re: Unknown Differential Ratio
Sorry for the confusion guys.
__________________
What's right about America is that although we have a mess of problems, we have great capacity - intellect and resources - to do some thing about them. - Henry Ford II |
09-19-2015, 11:19 AM | #18 |
Senior Member
Join Date: Apr 2015
Location: Albuquerque, NM
Posts: 441
|
Re: Unknown Differential Ratio
Well, I checked it out. This formula works! I have a 3.78.
Next, I will check the speedo cable. Sumpin' is wrong when I'm 10 mph off!
__________________
... prosperity is not the product of charity but of industry - HENRY FORD |
09-19-2015, 02:09 PM | #19 |
Senior Member
Join Date: May 2010
Location: new britain,ct 06052
Posts: 9,390
|
Re: Unknown Differential Ratio
Your cable is working. On the torque tube where the speedo cable attaches is a "turtle" housing the gear that drives the speedo cable. Remove it and count the gear teeth. It may be the wrong gear giving you the false reading. Replacement gears are available. Also try doing a search or someone may chime in what the correct gear (# of teeth) is.
Paul in CT |
09-19-2015, 05:52 PM | #20 |
Senior Member
Join Date: May 2010
Location: Between Seattle & Tacoma
Posts: 2,354
|
Re: Unknown Differential Ratio
I'm guessing your speedo magnet is weak and needs to be adjusted to get a correct reading. IF your odometer is correct. Odometer is mechanical driven and the speedo is residual magnetism .
|
|
|
Sponsored Links (Register now to hide all advertisements) |
|